Power & Energy Efficiency Handbook 2021

Advanced current sensing for next-gen electronics Page 10

Improvements in stacked load architectures Page 30

OCTOBER 2021

Gains from GaN Page 46

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POWER & ENERGY EFFICIENCY HANDBOOK

Talk of EV fires still smolders The latest figures from the National Fire Protection Association show that only about 20% of all vehicle fires arise from problems in the vehicle electrical system—most fires have something to do with the fuel system.

Seeing as electric vehicles will do away with problematic petrol, you might wonder whether a fleet composed mainly of EVs will experience fewer vehicle fires, despite recent headlines about five Chevy Volts igniting without any external cause.

Of course, here’s the rub: Car fires documented by the NFPA started in electrical systems powered by one or two 12-V lead-acid batteries.

In contrast, EVs carry behemoth 400 to 800-V battery packs spread out over the space beneath the passenger compartment. The issue is whether EV designers can balance safe operation with realities of charging, cost, and battery life.

You get a feeling for some of these tradeoffs from remarks made at the recent Battery Show in the Detroit area. There representatives from EV pickup maker Atlis Motor Vehicles, infrastructure engineering firm Black & Veatch, EV motorcycle maker Damon Motors, and battery maker Romeo Power sat on a panel that outlined a few of the obstacles to progress in battery technology.

Some of their comments pertained specifically to thermal runaway conditions in batteries which, obviously, can lead to outcomes involving fire departments. There is a lot of work underway in what’s called passive thermal propagation in battery packs. Basically, this refers to the heat generated during single-cell failures within high-energy batteries. The heat can force adjacent cells into thermal runaway, creating a cascading propagation through the whole battery.

One approach that can slow these potentially catastrophic effects is the use of passive mitigation strategies. Examples include putting 5-mm gaps between select rows and columns in the array of battery cells and

inserting physical barriers such as ceramic fiber board into the gaps.

Problem is, adding gaps and barriers makes the battery bigger and less energy dense. That’s definitely not the direction battery suppliers and automakers want to go, given the demand for ordinary EVs able to travel 600 miles before needing a recharge.

The tradeoff between energy density and thermal runaway problems also explains another trend: The steady growth in battery energy density seen over the past few years is starting to flatten out, panelists said. Thus EV batteries are still improving, but the improvements are taking longer to reach consumers.

Nevertheless, the companies making batteries and sophisticated EVs seem to believe that the problems presented by thermal issues and higher energy densities are solvable. Today, the cost of manufacturing EV battery cells is below $100/kWh. Panelists think within five years it will be less than $50/kWh. But they also think the battery industry will have to change to get prices this low. For one thing, battery manufacturing processes are still too expensive. Panelists say gross profit margins for battery manufacturers--which tend to be in the 10–20% range today--will have to come down to perhaps 8%, the average margin enjoyed by a clothing retailer. Additionally, future batteries must move away from using conflict materials, natural resources extracted in conflict zones and sold to fiance the fighting.

If it all comes true, you probably won’t have to worry about packing a fire extinguisher in the back seat of your EV.

LELAND TESCHLER • EXECUTIVE EDITOR 2

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CONTENTS P OWE R & E N E RGY E F F I C I E N C Y H A N D B O O K • O C TO B E R 2 0 2 1

02

TALK OF EV FIRES STILL SMOLDERS

06

HOW TO KEEP TRANSIENTS FROM DISRUPTING LOW-POWER CIRCUITS

IT CAN BE CHALLENGING TO GIVE A HIGHLY DYNAMIC LOAD A STABLE VOLTAGE WHEN THE POWER SUPPLY SITS SEVERAL FEET AWAY FROM THE DEVICE UNDER TEST.

10

ADVANCED CURRENT SENSING FOR NEXT-GEN ELECTRONICS

CONTACTLESS CURRENT SENSING PROVIDES THE FAST RESPONSE THAT STATE-OF-THE-ART POWER CIRCUITS DEPEND ON.

13

THERMAL CHALLENGES WITH HIGH-POWER RESISTORS

SHRINKING COMPONENT SIZES HAVE COMPLICATED THE TASK OF ENSURING TEMPERATURES STAY BELOW THEIR ALLOWABLE MAXIMUM.

15

POWER BRICKS GET AN ENERGY EFFICIENCY BOOST WITH GaN

THE DESIGN OF AN LLC RESONANT CONVERTER ILLUSTRATES HOW EGAN FETS CAN SHRINK THE PHYSICAL SIZE OF MODERN SUPPLY CIRCUITY.

20

HARVESTING ENERGY FROM OCEAN WAVES

EFFICIENT POWER CONVERSION TECHNOLOGY NOW MAKES BUOY SYSTEMS PRACTICAL FOR POWERING REAL-WORLD DEVICES.

26

INSIDE A MODERN POWER MANAGEMENT IC

PMIC S TODAY DO A LOT MORE THAN JUST REGULATE VOLTAGES. HERE’S A LOOK AT HIGH-END FUNCTIONS THESE DEVICES PROVIDE.

30

IMPROVEMENTS IN STACKED LOAD ARCHITECTURES

STACKED-LOAD SCHEMES HAVE MADE POWER CONVERSION MORE ECONOMICAL IN SERVER RACKS. NEW DEVELOPMENTS IN THIS TECHNOLOGY PROMISE TO PROVIDE ADDITIONAL GAINS IN EFFICIENCY.

34

THE EVOLUTION OF SMART MOSFET TECHNOLOGIES

A REVIEW OF MOSFET ADVANCES HELPS PREDICT WHERE THE TECHNOLOGY IS LIKELY TO HEAD.

38

IDENTIFYING THE RIGHT MEDICAL POWER SUPPLY

SPECIAL CONSIDERATIONS APPLY FOR POWER SUPPLIES WHEN EVEN SMALL ELECTRICAL CURRENTS POSE A SHOCK HAZARD.

42

CLEARING UP CONFUSION ABOUT TRACKING MULTIPLE CURRENT LEVELS

MULTICHANNEL POWER MONITORS HELP SIMPLIFY BATTERY-BASED SYSTEMS EMPLOYING MULTIPLE CURRENT SENSORS.

46

GAINS FROM G A N ENERGY EFFICIENCIES MADE POSSIBLE BY GALLIUM-NITRIDE SEMICONDUCTORS ARE STARTING TO IMPACT EVERY DAY PRODUCTS.

22 COMPARING IGBT AND SiC MOSFET PIMs IN SOLAR INVERTERS

SIDE-BY-SIDE PERFORMANCE COMPARISONS CAN SHOW WHERE SILICON-CARBIDE EXCELS IN PV INSTALLATIONS.

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How to keep transients from disrupting low-power circuits It can be challenging to give a highly dynamic load a stable voltage when the power supply sits several feet away from the device under test.

Bill Griffith • Keysight Technologies

Today’s integrated circuits put a highly dynamic load on their power supply.

This behavior poses a challenge during testing when IC power comes from programmable power supplies. The highfrequency current waveforms can lead to voltage drops at the integrated circuit. If severe enough, the voltage drop can, for example, reset a microprocessor or cause anomalous test results. It is important to understand why the voltage drop arises and how to minimize the voltage drop.

First consider the type of supply powering the DUT. The best possible output voltage regulation traditionally comes from linear power supplies. However, linear supplies tend to be large, expensive, and highly inefficient.

Recent advances in switching technology make it possible to replace linear supplies with switching power supplies in performance applications. Switching supply designers face seemingly contradictory goals of low output noise, fast transient response, low cost, and high density. Low output noise usually comes thanks to multiple filtering stages or larger filter components. This approach can be expensive and exhibits a slow transient response. It also is characterized by a low power density because of the size of the components. More advanced power supplies employ higher switching frequency, better filter design, and more sophisticated control topologies to optimize all the criteria. When selecting a power supply for IC testing, it is essential to examine the voltage transient response specification and output impedance to ensure good performance.

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OPTIMIZING LOAD WIRING In many cases, physical constraints force the power supply to sit several feet away from the IC test board, necessitating at least a few feet of load-lead wiring. Load lead wiring impedance can quickly degrade the source impedance the IC sees. Almost all programmable power supplies provide sense lead inputs. These let the operator make the point of voltage regulation be the location of the sense leads.

In an IC testing application, the sense point would be as close as possible to the IC. However, the voltage regulation loop can suppress voltage transients at this sense point only within its control bandwidth.

Consequently, a voltage transient can happen at this sense point if the current transient rises sufficiently fast. Load lead impedance at these lower frequencies can be modeled as a lumped series inductance and resistance.

Let’s examine a 25-A application with 5-A transients where the power supply is set to 2.5 V and connected to the IC test board via five feet of 14 AWG wire. Because this is a low-voltage application, voltage 10 • 2021

Simplified power supply output impedance and load lead impedance.

undershoots greater than 100 mV are generally unacceptable. The 14 AWG wiring has 2.5 mΩ/ft of resistance, so the round-trip connection between the power supply output and the IC test board has 25 mΩ of resistance.

The power supply voltage-control loop will compensate the calculated 125 mV drop after a period commensurate with its bandwidth. However, in the meantime, the IC will experience this 125 mV of voltage drop. In this application, the effect of the load lead resistance alone is enough to cause an unacceptable short-duration drop at the test board. However, the load lead inductance is another major cause of voltage drop. It is not uncommon for the test board to ramp the 5-A transient in 10 μsec. This high rate of current change can cause eeworldonline.com

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LOW CURRENTS in response to the change in output current.

More specialized cabling options such as custom coaxial cables or flat wire cables can reduce the inductance to as low as 10 nH/ ft. However, these options are costly and not as readily available. An alternative is lowimpedance energy storage located close to the test board.

USING A LOCAL BYPASS CAPACITOR Load lead network with bypass capacitance.

a constant voltage drop across the leads during the current ramp.

Load lead inductance changes depending on the loop area formed by the positive and negative lead. Using an approximation of the inductance, you can estimate the voltage drop. In most cases, 250-nH/ ft inductance is a good model for non-twisted load wiring.

Combining the effect of the resistance and inductance leads to:

The power supply cannot compensate rapidly enough for the voltage drop across load leads and the drop across its output, so you need a local source of energy. Capacitors are well suited to provide low impedance at high frequencies to complement the power supply low impedance provided at low frequencies. Many different capacitor technologies are available, and the process of finding the right part or a combination of components can be difficult.

Ceramic capacitors are well suited for high-frequency bypassing at low voltages. However, even with recent advances in ceramic capacitor technologies, they cannot match the high density and low price of aluminum electrolytic and conductive polymer aluminum solid electrolytic capacitors.

The equivalent series resistance of the bypass network is an essential parameter because it appears in series with the capacitor and can make the bypass network significantly less effective. Selecting a capacitor with the lowest possible voltage will help keep ESR low and capacitance density high.

The interaction between the power supply voltage-control loop, the load-lead network, and the bypass capacitance can be a bit complex.

However, some simple approximations can help with the initial value selection for the capacitor.

CALCULATE PEAK NETWORK IMPEDANCE The result of 1.375 V is unacceptable. As mentioned previously, the power supply voltage regulation loop will sense this voltage transient and adjust the supply output enough to maintain a steady 2.5 V at the test board. However, this process can take up to a millisecond even with a high-quality power supply. To reduce the lead inductance, tightly couple the force leads together by either tying them at regular intervals or by simply twisting them together. Twisting the leads also provides the added benefit of better immunity to other magnetic fields potentially caused by different load leads carrying large current transients. A good model for twisted leads is a 170-nH/ft inductor. This inductor includes both the positive and negative lead inductance effects. Recalculation with twisted leads yields:

Although the voltage drop has diminished, the total result is still unacceptable. Further improvement can be had by paralleling cable runs. For example, paralleling four sets of twisted cables will reduce the resistance and inductance by a factor of four.

Determine the desired peak impedance of the load lead network and bypass capacitance using the following expression:

Set the desired peak impedance equal to the expression for the characteristic impedance of the L-C tank formed by the load lead inductance and the bypass capacitance. Solve the expression for the value of capacitance:

The power supply must have an output impedance lower than the characteristic impedance of the L-C tank. Otherwise the calculation will not predict system behavior. The power supply output impedance will drop with decreasing frequency. In a case where the power supply output impedance is higher than the desired peak impedance, pick a tank resonant frequency to equal the frequency at which the power supply output impedance is less than or equal to Zpeak. The resonant frequency must be lowered by use of a larger bypass capacitor.

The goal of 100 mV is still out of reach, especially considering that the power supply will contribute an additional transient voltage drop eeworldonline.com

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10 • 2021

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7

POWER & ENERGY EFFICIENCY HANDBOOK

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Actual measurements of an N7950A with and without local capacitance storage.

Proper damping of the resonant tank is crucial. An improperly damped tank will tend to ring and can also destabilize the power supply control loop. The combination of the load lead resistance and capacitor ESR will damp the resonant tank. We will target a damping ratio of 0.5 for faster response and lower peak voltage by equating the tank resistance to the L-C tank characteristic impedance.

It may not be possible to find one capacitor with the right capacitance and ESR, but you can use parallel combinations of capacitors with different values and ESRs to arrive at the desired parameters.

The nearby figure shows the transient voltage response observed at the load when using the Keysight N7950A dynamic dc power supply. It excels in low-voltage, high-current situations and exhibits a low output impedance, perfect for this application. The light blue trace represents the four twisted pairs of cables without a local capacitor. Dark blue is the response from adding a 530 µF capacitor, as calculated in Equation 7. Boosting the capacitance by four times drops the tank impedance by a factor of two and yields the results shown in red.

Although load-lead impedance of lengthy cable runs can severely degrade the transient response performance of a high-performance power supply, mitigation practices can help realize the required performance. Twisting load-lead wiring to minimize the loop area formed between the supply and return lines, use of flat copper, or heavy gauge coaxial cables can significantly reduce the load-lead inductance. Properly sizing a bypass capacitor network at the DUT can further improve voltage level stability in the face of fast DUT current transients.

REFERENCES Keysight Optimize Power Source Integrity Under Large Load Transients application note, https://www.keysight.com/us/en/assets/7018-04181/application-notes/5991-3583.pdf

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Advanced current sensing for next-gen electronics Michael DiGangi • ACEINNA

The next generation of electronic products will be more powerful and flexible than ever.

The advanced circuitry to drive them needs intelligent power management to realize the desired performance.

Application spaces like robotics and microelectromechanical systems (MEMS) rely on higherperforming current-control systems. That’s where the current sensor comes in.

The explosion in portable and remote smart devices in the Cloud-enabled IoT has forced the industry to address energy storage. Issues go beyond increasing the energy density and charge/discharge rate. There must be intelligent monitoring of both the state of battery cells and their performance in the circuit. Parameters from temperature to output current must be known in real time.

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Contactless current sensing provides the fast response that state-of-the-art power circuits depend on.

The alternative to intelligent power management is brute-force approaches like fuses and circuit breakers. The problem is this approach risks catastrophic failure of the battery pack from thermal runaway or other types of failures. Breakers and switches work in lowpower applications but rapidly run out of legroom in fast-switching high-power electronics.

A good example can be found in EV lithium-ion batteries. They require constant monitoring to protect against situations like high temperatures, overcharging, problematic discharging, short-circuits and other failure events. These can arise during both charging and use, but the high currents involved in EV rapid-charging systems make the charging process a serious safety issue demanding intelligent power management.

State-of-the-art batteries used in the e-mobility and energy sector require a specialized Battery Monitoring Sensor (BMS) to cope with operational and safety requirements. These systems typically employ advanced monitoring devices such as ACEINNA’s current sensors that provide fast, accurate and bidirectional current measurement.

The high energy densities and accelerated charge/discharge times of modern battery technology has fostered more stringent requirements for current sensing. High energy-density batteries such as lithium iron phosphate (LFP) or lithium-titanate (LTO) require coulomb counting to determine battery state of charge (SoC), state of health (SoH), and state of function (SoF). (The Coulomb counting method measures the discharging current of a battery and integrates the discharging current over time.)

EV manufacturers are trying to reduce charging time by increasing the working 10 • 2021

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CURRENT SENSORS voltage. So EV battery voltages are rising, currently as high as 800 V. Silicon carbide (SiC) devices are well suited to operating at these voltages, as the variation of the transistor collector or drain current in the active or the saturation region of operation with the VCE or VDS is less than that of ordinary silicon-based transistors.

Next-generation EV chargers need advanced current measurement to detect faults fast and get real-time performance information. To address issues raning from ground faults to extreme loading conditions, current sensors provide feedback for the control loops in advanced charging systems.

Also important in EVs (and in many industrial motor-drive applications as well) is the traction inverter. Advanced current sensing here serves as a proxy for torque control.

SENSING TECHNIQUES Shunt current sensors are basically low-value, precision resistors. They sit in the conduction path between a power source and a load. The voltage drop across the resistor is proportional to the current flowing through it. to determine the current flowing through it. Shunt resistors have a maximum current rating, and the resistance value is typically given by the voltage drop at the maximum current rating. For example, a shunt resistor rated for 200 A and 50 mV has a resistance of 50 /200 = 0.25 mΩ. The voltage drop at maximum current is typically rated at 50, 75 or 100 mV. Resistive current shunts have limitations at high and low currents. At high currents the resistive material in the shunt itself can heat up enough to change the resistance. Shunt resistors usually have a derating factor of 66% for continuous operation, meaning a run time longer than two minutes. High temperatures degrade the accuracy of the shunt. Above 80 °C, thermal drift starts and worsens as temperature rises. Above 140°C the resistor may be damaged, and the resistance value may permanently change.

In contrast, such problems typically don’t affect contactless current sensors. Examples include contactless ACEINNA current sensors. They provide galvanic isolation and the load and consume no load power.

In addition, contactless sensing enables faster readout while correcting offsets via active feedback loops, adjusting the gain parameters and actively compensating the sensor offset. Integrated sensing also offers

An Aceinna contactless current sensor.

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Current sensors are essential for ensuring safety and performance in the dc fast charging of electric vehicles.

significant footprint savings over board assembled approaches. Built using an op-amp and comparator, the size of a discrete implementation will be larger than an IC version.

Overcurrent sensing is important not just for high-power applications like EV chargers. It’s also key for protecting delicate electronics in applications like in-patient medical sensors. Currentsensors like those from Aceinna are well suited for detecting overcurrent thanks to their fast response and large current measurement range.

Because they are isolated, contactless current sensors can be used on both the high and low sides of the circuit. Used along with AMR sensors (Anisotropic Magneto-Resistive sensors are contactless and measure the changes in the angle of a magnetic field as seen by the sensor and can be used for presence detection.) and temperature correction, they reduce the complexity of the customer design.

Current sensors also play a role in measuring power factor for ac power factor correction (PFC) circuits. PFC circuits reduce the harmonic distortion in the supply current and create a current waveform close to a fundamental sine wave to increase the power factor to unity.

Power factors below one result in more current needed to perform the same work. PFC produces reactive energy in opposition to the energy absorbed by loads such as battery chargers close to the load to improve the power factor. Aceinna current sensors not only simplify the overall system design, they also reduce the cost of implementation.

In a nutshell, application spaces like in-home fast charging require use of advanced current sensing to optimize the WBG-based systems in the latest power-management solutions.

REFERENCES ACEINNA, www.aceinna.com

10 • 2021

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HEAT DISSIPATION

Thermal challenges with high-power resistors Shrinking component sizes have complicated the task of ensuring temperatures stay below their allowable maximum.

Kory Schroeder • Stackpole Electronics Inc. Electronic components of all types continue to shrink in size. In response, resistor manufacturers are devising resistors with higher power ratings but which come in commonly used sizes. Of course, when more power gets dissipated in a smaller package, it is important to consider the impact on thermal issues.

Chip resistor technology is evolving rapidly.

Materials used in the construction of the resistor greatly impact how quickly and efficiently the part deals with the thermal energy it generates. The amount of heat that a particular resistor can dissipate depends on the specific heat of its materials and is proportional to the mass of the material used.

For example, metal alloy resistors, whether wire-wound or made with low resistance alloys for current sensing, will exhibit better thermal conduction and have more mass than similar resistors with film elements. Consequently, metal alloy resistors typically have higher power ratings.

What is more interesting, however, is the recent improvements in rated power for chip resistors of a given size. If we assume a size 2512 chip resistor with a metal element, there are currently power rating options ranging from 1 to 3W. In some cases, manufacturers may add a heat sink to the body of the resistor or make it thicker to better handle the additional heat. But in most cases the resistive element and the part itself are largely identical for the 1-W and higher power versions. Given that the amount of heat a chip resistor can dissipate depends on both the materials used and the amount of material present, it seems illogical that the same part can be rated at both 1 and 3 W. The key factor to understand is how hot will the part get in the application and whether the part can withstand this level of heat.

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The nearby chart shows the hot-spot temperature of a 2512-size all-metal currentsense resistor. The 2512-size chip resistors, even dissipating 1W of power, will generate enough heat to create PCB design and layout challenges. Most manufacturers recommend a hot spot/terminal temperature of between 105 and 125ºC depending on the element material. This is the combined temperature on any resistor due to power dissipated and ambient air. Film resistors will typically have recommended terminal temperatures at the lower end of the spectrum while metalelement resistors will typically tolerate higher temperatures. At 1 W, the resistor may see temperatures of 115ºC which is acceptable for robust metal- element sense resistors.

However, the 1.5, 2, and 3-W-rated parts show

A typical 50 mΩ chip resistor in a 2512-size package.

Hot spot temperatures for chip resistors in a 2512-size package.

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POWER & ENERGY EFFICIENCY HANDBOOK hot spot temperatures well above 125ºC. This hot-spot data implies that thermal reduction techniques are necessary when these parts are used at the higher power ratings,.

Thermal reduction strategies vary widely in cost. Their effectiveness varies with the application and surroundings. Convection cooling from fans may be practical in some industrial applications but not in small consumer electronics. Other methods such as the use of larger solder pads, copper traces of a heavier weight, larger traces, vias through the PCB, and heat sinks are all candidates. Components that either absorb heat (transformers or large inductors) or that can’t tolerate it (certain semiconductors) must be kept away from resistors running at high power. This distancing may be tough to accomplish in designs that require small footprints. These problems may force the use of more robust semiconductors along with multiple heat reduction methods.

Similar design considerations are necessary when using downsized chip resistors. A standard 1206-size chip may work for thick-film devices requiring a quarter-watt power rating. However, high-power 0603-size chip resistors are now readily available. These reduce the overall space needed (including solder pads and traces) by 66% or more depending on manufacturer recommendations. The significance of this size savings depends on the total circuit area and other factors such as trace routing. But the size reduction can be dramatic when multiple parts are replaced in this manner.

A similar relationship holds for the heat increase accompanying this size reduction. The nearby chart shows the net rise in hot-spot temperature is only around 10ºC. But suppose five such resistors are downsized. The aggregate thermal impact would typically be greater than five times the individual delta, especially if those resistors sit near each other. The co-heating from neighboring resistors makes it more difficult to dissipate heat. Ditto for heat absorbing components such as large wound transformers or toroidal inductors.

Depending on the PCB design, replacement of multiple chip resistors with smaller high-power versions can easily add 15 to 40 degrees of heat.

For high density applications, even a reasonable combination of heat reduction methods may not be enough to deal with this kind of heat rise.

Thus it may not be feasible to replace numerous resistors with smaller chip-packaged versions having higher power ratings.

All in all, current trends toward compact

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DESIGN WORLD — EE NETWORK

Comparing hot-spot temperatures between quarterwatt 1206 and quarter-watt 0603-size resistors.

personal electronic devices make it desirable to use smaller components. Smaller components with higher power ratings are now readily available, but the net effect of close spacing makes it tough to keep surface-mount chip resistors below their 105 to 125ºC hot-spot temperature max. Keeping components below their maximum terminal temperature ensures stable operation and longer circuit lifetime.

REFERENCES Stackpole Electronics Inc., https://www.seielect.com/

10 • 2021

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GAN CONVERTERS

Power bricks get an energy efficiency boost with GaN The design of an LLC resonant converter illustrates how eGaN FETs can shrink the physical size of modern supply circuitry.

Alex Lidow Efficient Power Conversion Corp.

The rapid expansion of computing and telecommunications has brought a migration to a 48 V-based power architecture.

Applications for this higher-voltage architecture include artificial intelligence, 5G, big data, and cloud servers demanding higher power density, higher power per board, and higher component density. Because real estate is extremely valuable on these highdensity computing boards, there is a high premium on power density.

Consequently, there is a lot of interest in 48-to-12-V on-board dc-dc converters. The Distributed-power Open Standards Alliance (DOSA) sets size limits on 1/8th power brick- format 48-V server applications. In that regard, consider a 1-kW, 4:1-conversion ratio, eGaN FET-based LLC resonant converter.

This converter hits 97.5% peak and 96.7% full-load efficiency. It can move beyond the limitations of the DOSA standard to realize even higher power density through use of GaN integration.

Typical specs in this application area are for a 1-kW load power-capable 48-to-12-V converter that operates in the range from 40 through 60 V. The converter design must fit in a volume defined by 58.4x22.9x10 mm, which is similar in size to a DOSA 1/8th-brick converter, with a maximum allowable airflow limited to 400 LFM. In addition, the final module had to be fitted with connection pins for either horizontal or vertical mounting.

Finally, the input and output needs no isolation, which presents simplifies both the topology and design.

DESIGN OVERVIEW In this design, a full-bridge, primary-side configuration generates the pulsed input voltage to the resonant tank circuit. The tank is comprised of a resonant capacitor in series with a resonant inductor by using the transformer leakage inductance.

The design uses a high-frequency planar transformer with 4:1 turns ratio designed as

The EPC9149 1 kW, 4:1 ratio, LLC resonant converter.

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10 • 2021

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15

POWER & ENERGY EFFICIENCY HANDBOOK

Circuit block diagram

a matrix transformer comprised of two series 2:1:1 connected sections wound around a single two-post core. The transformer magnetizing inductance in conjunction with a pre-determined dead time setting is used to establish zero-voltage switching (ZVS) on the primary-side FETs. Switches Q1/Q4 and Q2/ Q3 switch at near 50% duty cycle and at 180° out-of-phase with each other. Two parallel center-tapped half-bridge arms are used in the secondary side, together with synchronous rectifier FETs for the output. This synchronous rectification scheme reduces the secondary side conduction losses at high-load currents. eGaN FETs are well suited for softswitching LLC resonant converters. Compared to silicon MOSFETs of similar ratings, their lower gate charge (QG) and 5-V gate operation brings much lower gate power consumption.

In addition, GaN FETs have much lower output capacitance and thus need much less energy to realize ZVS. Lower output capacitance would either reduce the dead time and boost the effective power delivering time, or reduce the required magnetizing current, circulating energy and conduction losses. Finally, eGaN FETs are three to five times smaller than their aging MOSFET counterparts.

The design uses the 100-V, 3.2-mΩ EPC2218 and 40-V, 1.5-mΩ EPC2024 for the primary- and secondary-side power devices respectively. Both eGaN FETs can operate at up to 150°C junction temperature. The small form factor of GaN FETs make it possible to

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A combination of custom-shaped heat spreaders and a finned heatsink for the top and bottom side of the EPC9149 board were designed to be added to the 1 kW converter.

fit eight FETs in the limited 1/8th power brick size for the synchronous rectifiers.

The design also includes on-board housekeeping power supply, digital controller, and input and output voltage sensing. To command the power stage, a dsPIC controller (dsPIC33CK32MP102-I/2N) from Microchip generates high-resolution PWM signals.

The on-board housekeeping power supply generates the 5 V needed for the gate drivers and the 3.3 V for the controller.

A combination of custom-shaped heat spreaders and a finned heatsink for the top and bottom side of the EPC9149 board were

designed to be added to the 1-kW converter.

Copper heat spreaders sit on top of both primary- and secondary-side FETs to spread their heat to the outer structure. The copper heat spreaders include contour features that allow parts of the heat spreader to rest on the PCB to facilitate cooling, mechanical stability and define the correct spacing between the heat spreader and the FET top surfaces.

A high-performance thermal interface material (TIM)--such as T-global A1780 with high thermal conductivity of 17.8 W/m-K--provides

The EPC9149 1-kW, 4:1 ratio GaN FET-based LLC resonant converter.

10 • 2021

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GAN CONVERTERS insulation and high thermal conductivity between the components and the metal surface of heat spreaders. A 2:1 compression ratio provides adequate force for best thermal performance, but not so much compression as to mechanically stress any components. TIM also provides isolation for grounding the heatsink. A second thermal interface material--TG-A6200, also from T-Global, which has a thermal conductivity of 6.2 W/m-K-interfaced the heat spreader to the heatsink.

Mechanical screws on the board hold the entire mechanical structure in place.

The EPC9149 1-kW, 4:1 ratio GaN FET-based LLC resonant converter module was affixed to a motherboard for evaluation. The main input and output connections, measurement ports, bulk input and output capacitors, USB and communication port all sit on the motherboard.

The low gate capacitance, output charge and on-resistance and the small form factor of the eGaN FETs are keys to high efficiency at a power density exceeding 1,227 W/in3.

The EPC9149 is an example of the state-ofthe-art for 48-to-12-V on-board dc-dc converters.

There are ways to further improve power density.

First, the long-and-thin aspect ratio of design was forgone for a squarer format that allowed significant improvement in the transformer design. The second improvement was driven by a 3D assembly approach where the transformer was separated from the power converter stage. This approach allowed improvement of both designs with fewer compromises.

The next improvement is to upgrade to the next generation of eGaN FETs. For the followon design, the 40-V, 1.5 mΩ device used on the EPC9149 is upgraded to a 40-V, 1 mΩ device.

The combination of these improvements brings a power density of 5,130 W/in3 – a huge leap forward!

LLC resonant converter overall power loss and efficiency, including the housekeeping power consumption, at 48-V input and 12-V output. This converter has a 97.6% peak efficiency and 96.7% full-load efficiency.

GAN INTEGRATION In 2014, EPC devised the first GaN integrated circuits, monolithic half bridges. The advantages of this integration included reductions in both size and cost and, by virtue of the close coupling of the two transistors, reduction of the parasitic common-source inductances.

In early 2019, the driver function and the monolithic half bridge were merged onto a single GaN-on-silicon substrate along with a level shifter, synchronous boost circuit, protection, and input logic. This complete EPC2152 ePower Stage can be driven at multi-megahertz frequencies and controlled by a simple low-side CMOS IC.

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Exploded view of the EPC9159 48-to-12-V bi-directional LLC converter. In this 3D assembly, the transformer sits on top of all the PCB components.

The controller and bias supply are sandwiched between the transformer and the base PCB. Finally, the edge copper bars for making connections using castellated connections on the boards connect the entire structure together.

The upgraded FETs, improved transformer design, and 3D assembly enable this converter to get to a power density of 5,130 W/in3.

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DESIGN WORLD — EE NETWORK

17

POWER & ENERGY EFFICIENCY HANDBOOK eGaN ICs

With the addition of just a few passive components, it can become a complete dc-dc regulator. This regulator is 35% smaller and has half the components of a discrete implementation with a higher efficiency. In the next few years, there will be complete system-on-a-chip designs that include all the main functions required for a state-ofthe-art dc-dc converter.

The impact of this integration on the 48–12-V onboard dc-dc converters will be dramatic. Implementing eGaN power stage ICs on the primary side and synchronous rectification ICs on the secondary side doubles the amount of area that can be used for the GaN circuits. This integration greatly reduces and will eventually eliminate housekeeping circuits and controllers. The estimate is that the losses due to GaN and the peripheral components can be halved to yield an additional 50% higher power density.

The trend toward higher power density is not abating. eGaN devices provide a way to realize the maximum power density possible today, and the next generation of devices and integrated solutions will take advances even further.

Efficient Power Conversion Corp. (2021), EPC2024 datasheet, EPC2024 – 40 V, 90 A Enhancement-Mode Power Transistor, [Online] https://epc-co.com/epc/Portals/0/epc/ documents/datasheets/EPC2024_datasheet.pdf Microchip Technology Inc., dsPIC33CK32MP102-I/2N datasheet, 100 MHz Single-Core 16-Bit Digital Signal Controller. [Online] https://www.microchip.com/en-us/ product/dsPIC33CK32MP102 EPC9149 Efficient Power Conversion Corp. (2015), EPC9149 Quick Start Guide, EPC9149: 36 – 60 V Input, 9 – 15 V Output, 83 A Output Fixed Conversion Ratio 1 kW LLC, 1/8th Brick size Module Quick Start Guide, [Online] https://epc-co.com/epc/Portals/0/epc/documents/guides/ epc9149_qsg.pdf

REFERENCES

T-Global Technology, TG-A1780 datasheet, TGA1780 Ultra soft thermal pad, [Online] http://www. tglobaltechnology.com/uploads/files/tds/TG-A1780.pdf

A. Lidow, editor, GaN Power Devices and Applications, 1st ed. Power Conversion Press, 2022. ISBN: 978-09966492-2-3 [Online] https://epc-co.com/epc/Products/ Publications/GaNPowerDevicesandApplications

T-Global Technology, TG-A6200 datasheet, TGA6200 Ultra soft thermal pad, [Online] http://www. tglobaltechnology.com/uploads/files/tds/TG-A6200.pdf

A. Lidow, M. de Rooij, J. Strydom, D. Reusch, J. Glaser, GaN Transistors for Efficient Power Conversion, 3rd ed., J. Wiley 2020. ISBN-13: 978-1119594147 [Online] https://epc-co.com/epc/Products/Publications/ GaNTransistorsForEfficientPowerConversion.aspx

18

Efficient Power Conversion Corp. (2021), EPC2218 datasheet, EPC2218 – 100 V, 231 A Enhancement-Mode GaN Power Transistor, [Online] https://epc-co.com/epc/ Products/eGaNFETsandICs/EPC2218.aspx

DESIGN WORLD — EE NETWORK

10 • 2021

Efficient Power Conversion Corp. EPC2152 Datasheet, EPC2152 – 80 V, 15 A ePower™ Stage. [Online] https:// epc-co.com/epc/Products/eGaNFETsandICs/EPC2152.aspx

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POWER & ENERGY EFFICIENCY HANDBOOK

The C-Power SeaRAY.

Harvesting energy from ocean waves Efficient power conversion technology now makes buoy systems practical for powering real-world devices.

Autonomous offshore power systems (AOPS) now capture mechanical wave energy and convert it into usable power for a wide range of oceanic applications such as offshore oil and gas exploration and production, offshore carbon sequestration, oceanographic research, aquaculture and homeland defense.

An example comes from Columbia Power Technologies, Inc. (C-Power) in Corvallis, Ore. Its systems provide kilowatt-scale power for offshore data communications networks and were initially devised through a Darpa project called Wave Energy Buoy Systems (WEBS).

C-Power’s latest AOPS device is called the SeaRAY. SeaRAY replaces electric tethers fed from a ship or diesel generator that have historically powered underwater vehicles, subsea operating equipment and open-ocean sensors.

Now, the SeaRAY device generates power from waves by acting like a large buoy with arms.

Waves move the arms up and down creating relative motion between the float and body of the buoy. The bigger the wave, the higher the

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DESIGN WORLD — EE NETWORK

10 • 2021

power pulse. The arms are mechanically coupled to an electric generator.

At the top and bottom of the wave motion, the generator is not moving. The velocity of the arms increases from zero to some peak (based on wave size). This motion causes the generator to turn, accelerating rotationally to some max RPM. Then it decelerates, stops, and repeats for each wave. This process is cyclical with the stochastic waves.

The resultant voltage coming out of the generator has a continuously varying amplitude at a continuously varying frequency. The bigger the wave, the larger the amplitude of the voltage envelope and the larger swing in frequency. The electrical power, voltage and current, is converted to usable energy via power electronics and energy storage.

The key power design challenge for C-Power was to reconcile complex ocean wave energy properties with the demanding power conversion requirements of the SeaRAY. This included an ultra-wide 30:1 input range, which reflects the unpredictable nature of ocean waves. The SeaRAY power conversion technology is from Vicor Corp.

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ENERGY HARVESTING

The SeaRAY design makes remote, autonomous data communications possible by sending information from the ocean to the cloud.

The power supply converts the energy from the generator and feeds a continuously varying current into a large bank of super capacitors. The energy from the capacitors is used to maintain a charge on the batteries and power auxiliary buoy systems. The power from the buoy can be used for any application. This process allows for high peak power conversion to supply energy to loads, including a small amount of power for the AOPS wave energy converter (WEC) supervisory control and data acquisition system. The batteries are there to supply power to the onboard equipment in case of calm water and no waves.

The scalable power design of the SeaRAY uses Vicor BCM fixed-ratio bus converters and PRM regulator modules with complex multistage discrete converters to efficiently convert turbulent, unpredictable wave energy and provide controlled power.

This enabled C-Power to increase the SeaRAY design’s conversion efficiency from about 50% to a range of 85 to 94%.

The Vicor Power Systems design

team delivered a unit capable of accepting external control signals from the C-Power system to match precise power conversion needs in real time. In addition, the power conversion topologies used in Vicor modules help to minimize electromagnetic interference and noise onboard the SeaRAY that could otherwise compromise sensor measurement accuracy.

“We really needed wide-range DCDC, something that we could control and regulate as we’re converting pulsed ocean wave power into a semi-stable DC bus,” said Joe Prudell, a C-Power senior R&D electrical engineer. “This is extremely challenging. Being able to do that at

various power levels using Vicor’s power modules really is an advantage.”

The SeaRAY design also makes autonomous, remote data communications possible by transmitting what happens in the ocean to the cloud in real time. Previously, marine data-gathering systems have been limited in the breadth and frequency of data collection. Using cellular networks and satellite communications to pass data in real-time between the cloud and the SeaRAY allows collection of more and richer data that can be delivered more often.

“There are plenty of companies trying to capture and convert wave energy, but it’s another thing to do something in a small, compact form factor and still satisfy what customers need from an operational and logistics perspective,” C-Power CEO Reenst Lesemann said. “That’s where we, with Vicor’s assistance, have been able to stick our chins out so much further than everyone else.”

REFERENCES Columbia Power Technologies, Inc., cpower.co.

Vicor Corp. www.vicorpower.com

SeaRAY uses the Vicor BCM fixedratio bus converter and PRM regulator modules with complex multistage discrete converters to efficiently convert wave energy and provide controlled power. Using power modules Vicor developed a power delivery network that improved the SeaRAY conversion efficiency from 50% to over 90%.

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21

POWER & ENERGY EFFICIENCY HANDBOOK

Comparing IGBT and SiC MOSFET performance PIMs in solar inverters Side-by-side comparisons can show Steven Shackell • ON Semiconductor

where silicon-carbide excels in PV installations.

According to the International Energy Agency, solar power (PV) installations are on track to reach an installed capacity of 3,300 TWh by 2030, a yearly growth rate of 15% from 2019.

Installations will be a mix of micro, mini and utility-scale, but all with similar PV technology: Cells will be connected in series for high, usable voltages and in parallel for higher power.

A trend is to increase voltages with strings of panels to gain the advantage of proportionally lower current, producing less power loss in connections and cabling. Typical nominal panel installation voltages are around 500 to 1,000 V but 1,500 V is predicted to eventually become more common.

Rather than using a single central inverter, each string will often have its own relatively low-power inverter for scalability, economy and fault tolerance. Typically, the PV voltage is boosted to a regulated dc value suitable for input to a dc-ac conversion stage. And a Maximum Power Point Tracking (MPPT) controller optimizes the load on the panel for best energy efficiency. The boost dc-dc converter and inverter are high-efficiency switching circuits, and the semiconductors employed can be of various technologies.

Insulated Gate Bipolar Transistors (IGBTs) have dominated high power dc-dc and ac-dc conversion, but new wide band-gap (WBG) semiconductors such as silicon carbide (SiC) MOSFETs are having an impact. Their ratings that compete into the tens-of-kilowatts range and even higher when paralleled.

Both technologies are available not only as individual devices in common packages, such as the TO-247, but also as power integrated modules (PIMs). A PIM is basically an industry standard housing that holds several switches, sometimes including diodes and even drivers and protection circuitry. With PIMs, a single package can provide a complete power stage for converter and inverter functions.

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IGBTs and SiC MOSFETs differ markedly in several respects. IGBTs are restricted to low frequencies because of their dynamic losses but drop a nominally constant saturation voltage when conducting. This behavior leads to a power loss simply proportional to current. SiC MOSFETs, in contrast, can switch at hundreds of kilohertz with low dynamic loss but exhibit a nominally constant resistance when conducting.

This behavior leads to a power loss proportional to the square of current, clearly an increasing disadvantage as power throughput rises.

Dynamic losses are frequency-dependent.

If IGBTs and SiC MOSFETs are compared at around 20 to 30 A switching at the same low frequency, say 16 kHz, conduction losses are similar but dynamic losses are quite different.

Consider two sources of switching loss, turn-on and turn-off energy Eon and Eoff respectively.

IGBTs have a lower turn-on loss at low current, but there is a crossover point; the Eon of both device types is at around one-quarter of the conduction losses, a little worse for IGBTs but not a large absolute value. However, Eoff is much higher with IGBTs because of ‘tail’ current. These are minority carriers that must

10 • 2021

IGBT and SiC MOSFET PIM voltage drop compared at 125°C, for a 50 A-rated IGBT PIM and a 38-A SiC PIM. The crossover point for best efficiency is at about 25 A, under otherwise similar conditions. The plots are for a junction temperature of 125°C which is typical for the application.

be swept out of the device N-drift region on turn-off, producing transient power dissipation.

There is around a factor-of-ten difference for Eoff between the device types.

It is useful to consider the differences between a practical PV boost converter based on a PIM-IGBT vs one using a PIM-SiC device.

A nearby table summarizes the two with an input of 500 V, 25 A and an output of 800 Vdc, running at 16 kHz and 95°C case temperature.

There is a clear overall power saving with SiC which exhibits a total loss of around a third that of the IGBT circuit and a lower junction temperature for higher reliability.

Besides energy savings, the benefit of better efficiency with SiC includes reduced size and heatsinking, a lower rise in temperature

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PIMS IN SOLAR INVERTERS TURN OFF LOSS (125°C)

for the same heatsinking or, alternatively, higher power throughput for the same heatsinking and temperature rise. In addition, it is worth investigating the high-frequency capability of SiC. Though the SiC devices have a higher junction temperature, as WBG devices, they typically are rated for 25°C higher operation than silicon.

SiC MOSFETs still show a significant efficiency gain over IGBTs and a little over half the losses.

However, operation at a higher frequency also allows use of a boost inductor physically smaller by around a factor of three with consequential cost and weight savings. Additionally, there can be less EMI filtering at the fundamental frequency and low harmonics with further savings.

But SiC MOSFETs do have fast rising and falling edges. So high-frequency filtering must be considered carefully to meet emissions standards.

Losses are not the only differences between IGBTs and SiC MOSFETs. For example, MOSFETs

TURN ON LOSS (125°C)

Dynamic losses of example IGBTs and SiC MOSFETs compared at 16 kHz. Eoff is much higher with IGBTs due to ‘tail’ current – minority carriers that must be swept out of the device N-drift region on turn-off. There is around a factor of ten difference for Eoff between the two types of devices.

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POWER & ENERGY EFFICIENCY HANDBOOK BREAKDOWN OF LOSSES IN AN EXAMPLE BOOST CONVERTER AT 16 KHZ PIM-IGBT

PIM-SiC

Conduction loss

13.33 W

12.17 W

Switching frequency

16 kHz

16 kHz

Turn on loss Eon

3.8 W

3.17 W

Turn off loss Eoff

34.66 W

3.06 W

Total loss

51.79 W

18.39 W

Tj (Tc = 95 °C)

137.9 °C

109.9 °C

spikes from any source or emitter inductance common to the gate drive loop.

Any device Miller (drain to gate) capacitance can also tend to spuriously turn devices on with high drain or collector voltage edge rates (dV/dt). Again, the negative gate drive helps to avoid problems.

SiC MOSFETs have much higher dV/dt and di/dt than IGBTs. Thus high-frequency layout techniques with careful decoupling are necessary to avoid unreliable operation and excessive EMI. Drivers must be close to the SiC MOSFET PIM. and any available Kelvin connection to the MOSFET source should be used as the driver return, to avoid common inductance.

It can be difficult to accurately measure the dynamic performance of SiC MOSFET PIMs due to the fast edge rates. Typically test equipment should have at least 300 MHz bandwidth and high-frequency measurement techniques are in order. Voltage probes should be connected with a minimum ground loop and current monitored with high-performance sensors such as Rogowski coils.

Making the switch from IGBTs to SiC MOSFETs is a net system benefit at increasing power levels, with PIMs providing an easy avenue. Those familiar with using IGBTs, however, should be aware that a simple swap-out will not give good results – optimum performance requires a re-evaluation of gate drive arrangements, layout and EMI filtering.

contain a body diode which is absent in IGBTs. The body diode can be useful in conversion stages that require reverse or ‘third quadrant’ conduction in the switch. The SiC MOSFET body diode can provide the conduction although its forward voltage drop is relatively high. So an extra parallel diode must be added when using IGBTs this way.

Thus there is a point where benefits from the use of SiC at a higher frequency are substantial enough to outweigh their additional PIM unit cost. SiC MOSFET on-resistance declines with every new generation of devices, so the benefit cross-over point continually rises to higher power levels

REFERENCES

SiC DESIGN CONSIDERATIONS

ON Semiconductor, www.onsemi.com

The gate drive for IGBTs and SiC MOSFETs may seem nominally similar. But the on-drive for the SiC device is more critical for lowest conduction losses. It must be as close as practical to the absolute maximum of typically 25 V. For this reason, 20 V is often used, giving some safety margin. Both device types are nominally off with a 0-V gate drive, but both are often driven negative by a few volts.

This gives smaller Eoff, less gate-source ringing on turn-off, and helps prevent ‘phantom turn-on’ which can result from

PV installed capacity projections, www.iea.org/reports/solar-pv String inverter trends, www.solarpowerworldonline.com/2018/11/ high-voltage-solar-systems-save-contractors-cash/

LOSSES COMPARED – IGBTS AT 16 KHZ AND SIC MOSFETS AT 40 KHZ PIM-IGBT

PIM-SiC

Conduction loss

13.33 W

13.6 W

Switching frequency

16 kHz

40 kHz

Turn on loss Eon

3.8 W

7.22 W

Turn off loss Eoff

34.66 W

8.34 W

Total loss

51.79 W

29.16 W

Tj (Tc = 95 °C)

137.9 °C (Tc = 95 °C)

133.6 °C (Tc = 110 °C)

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DESIGN WORLD — EE NETWORK

10 • 2021

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Power Film Resistors Caddock's Power Film Resistor Technology brings unique power resistor packaging options to the power system designer. The non-inductive designs of these power resistor products provide outstanding low reactance for power switching systems, high frequency circuits and other reactance sensitive applications. s.

Heat Sink Mountable with Non-Inductive Design Power rating is based on a +25°C case temperature. The thermal mounting issues are the same as with power semiconductors.

15 Watts

20 Watts

Model No.

Power Rating at +25°C Case Temp.

Resistance Range

MP915

15 Watts

0.02 Ω to 1K

MP825

25 Watts

0.02 Ω to 10K

MP820

20 Watts

10 Ω to 10K

Metal Mounting Tab

MP821

20 Watts

0.02 Ω to 9.99 Ω

Metal Mounting Tab

MP916

16 Watts

0.01 Ω to 0.019 Ω

MP925

25 Watts 500V max.

Low Cost Design Low Resistance Range

5K to 100K

MP930

30 Watts

0.02 Ω to 4.99K

MP850

50 Watts

0.2 Ω to 10K

TO-220 Style Package

MP2060

60 Watts*

0.005 Ω to 1K

TO-247 Style Package

MP9100

100 Watts

0.05 Ω to 100 Ω

Resistor Style

25 Watts

30 Watts

TO-126 Style Package TO-220 with Metal Mounting Tab

50 Watts

Clip-on 60 Watts

TO-220 Style Package

100 Watts

Comments Low Cost Design Standard Resistance Values Copper Heat Sink Integral in the Molded Package

Low Cost Design Standard Resistance Range Low Cost Design Extended Resistance Range Copper Heat Sink Integral in the Molded Package Clip Mount, Values to 0.005Ω *60 amps max. for 0.015Ω and below Highest Power Rating

Axial Lead - High Power with Non-Inductive Design Power rating is based on +25°C ambient, derated to zero at +275°C.

High temp. capability up to 275°C

High Performance Film Resistors from

CADDOCK

ELECTRONICS, INCORPORATED © 2019 Caddock Electronics, Inc. L-443.0319

Resistor Style

Caddock Type

Power Rating

Resistance Range

Comments

Axial Lead

Type MS 18 Models to choose from

0.5 Watt up to 22 Watts

20 Ω up to 30 Meg

These non-inductive resistors are about as inductive as a straight piece of wire the length of the resistor body.

Axial Lead Low Resistance

Type MV 5 Models to choose from

1.5 Watts up to 10 Watts

0.1 Ω up to 20 Ω

Low Resistance with EXTREMELY low inductance.

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For Samples and more Information contact Applications Engineering: Sales Office - USA and Canada Applications Engineering 17271 N. Umpqua Hwy. Roseburg, Oregon 97470-9422

phone: 541-496-0700 email: sales@caddock.com For Distributors listed by country see caddock.com/contact/dist.html The Caddock General Catalog includes specifications on over 250 models of high performance resistor products. Call for your copy or see us online at caddock.com

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product information at www.caddock.com

POWER & ENERGY EFFICIENCY HANDBOOK

Inside a modern power management IC PMICs today do a lot more than just regulate voltages. Here’s a look at high-end functions these devices provide.

Superior power management and high efficiency have become essential as electronics have become increasingly smaller and more streamlined. The reduction of power dissipation and consequent heat and thermal issues is critical to improving both battery life and the product reliability.

Key components are the high-efficiency regulators that handle a wide range of power requirements and remain efficient across a wide range of load currents. Likewise, high efficiency during heavy loads is critical for mitigating heat and power dissipation.

Narasimhan Trichy • Qorvo

A Power Management Integrated Circuit (PMIC) is an efficient and integrated way to distribute power in a complex system with multiple power rails or regulators. With configurable and adjustable functions and parameters, PMICs can be preprogrammed and optimized on the fly, using an I2C interface. Qorvo PMICs are firmware-compatible for easy control and suitable for dynamic power management in electronics requiring several low-power states.

With a socketed evaluation board,

SELECTING A SUITABLE PMIC Step 1: Identify the number of power rails required. A typical system may contain a multitude of subcomponents such as a main system controller or processor, sensors, a screen or graphical interface, and so on. Each of these may need to be enabled or disabled independently or can be combined to be powered from a single regulator if their functions can work from a similar

PMICs can be reprogrammed to create “instant samples” for users to test and evaluate. This eliminates the wait for factory programmed samples – a task that could take weeks. Qorvo tools also provide the ability to record the desired configuration (also referred to as the CMI or Coding Matrix Index) in a proprietary file format that Qorvo can then use to mass produce the units.

COMPARING A DISCRETE REGULATOR (BUCK) WITH AN INTEGRATED REGULATOR ON A QORVO PMIC

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PMIC TECHNOLOGY Evaluation Board for the ACT88760 is connected to the “Active CiPS” USB programming dongle.

Qorvo’s software GUI for the ACT88760 interfaces the I2C interface to the PC using software.

power supply and with the same voltage.

Determining the number of system power rails required can define the number of regulators required. Knowing the number of rails leads to picking a PMIC of appropriate size, able to handle the correct number of system rails, with a capacity matched to the appropriate system component.

Step 2: Identify the required capacity of each power rail. Typically, every regulator serves as a power supply to one or more system components. The maximum load current the regulator must support is the load requirement or necessary capacity. Thus each regulator should have enough load capacity to match or exceed the desired load. The maximum load current drawn by each of the components to which the regulator supplies power must be added to get the total load current requirement. In a nutshell, the regulator must provide a voltage range and output current that each rail needs..

Step 3: Consider the input power source.

A USB or single-battery system would use an input power source of 5 V or lower. A standard lithium-Ion/lithium-polymer battery has a useful voltage range of ~2.7 to ~4.4 V. Applications such as a laptop or desktop computer, or enterprise storage or computing, could use voltages up to 18 V. The input voltage of PMICs can differ, and the voltage range of the input power source must be lower than the maximum voltage rating of the PMIC itself. A higher-voltage PMIC may be used in a lowervoltage system but not vice versa.

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System functions could include system reset signals, power-good signal generation, power sequencing during power- up, power-off sequence when turning off components, lowpower states when power saving is enabled, battery/ input-voltage monitoring for underand over-voltage detection, fault detection in regulators, fault reporting and diagnostics, interrupt functions, push-button interface, GPIO wake and trigger functions, signal voltage level shifting, controlling external regulators, monitoring external regulator outputs for power-good, and many others.

A suitable PMIC with adequate GPIOs and system functions can minimize the need for external components and minimize the overall cost of the system. Integration of most system functions into the PMIC also reduces the system footprint. These system functions are critical but are easily overlooked when comparing costs and simplicity of PMICs to discrete solutions.

Firmware compatibility is an important aspect for modern electronics. Many applications today are battery powered. One way to lengthen battery life is by tweaking power sequences, adjusting low-power-mode behavior, lowering voltage, and adjusting current supplies dynamically when they are lightly used. Firmware upgrades can implement such tweaks well after the products are deployed in the field.

Over-the-air upgrades are now ubiquitous and demand a level of sophistication in power management that Qorvo PMICs offer.

The use of multiple time programmable

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(MTP) and non-volatile technology lets Qorvo PMICs be programmed more than once, and programming can take place in the field. (MTP is a kind of non-volatile memory manufactured via a relatively simple, economical process.) This technology helps create field-programmable products, but the goal is to avoid any firmware intervention or programming. It is desirable to configure PMICs so there is little need for firmware support and to ensure they function autonomously, supporting firmware control only when necessary.

It is useful to compare a general-purpose buck regulator with a typical integrated regulator from Qorvo, the ACT88760. The regulators on Qorvo PMICs require just three components – an inductor, an output capacitor and an input capacitor. By comparison, it might take more than 10 components to implement similar functions using stand-alone regulators.

The integrated regulators on Qorvo PMICs have features such as adjustable output voltage, adjustable peak inductor current and output current, power-good output, current-limit protection, overvoltage and undervoltage detection, and numerous others. They can interface with GPIO pins on the PMIC to provide status or take inputs to control each regulator.

Designers traditionally like the control that discrete components provide. The designer can choose different components and a means to adjust external resistors to set voltages, control current limits or change on/off times for each power supply. Qorvo PMICs offer the same

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POWER & ENERGY EFFICIENCY HANDBOOK CONFIGURABLE, MULTI-TIME PROGRAMMABLE POWER SOLUTIONS - ACTIVECIPS SAME PMIC IN DIFFERENT APPLICATIONS

ACT88760 is a highly integrated PMIC that can be used for many applications.

controls but without soldering or replacing components. Modifications are via the press of a button using the Qorvo-supplied software GUI on a USB dongle that interfaces the PMIC to the software GUI. As an example, the output voltage of most regulators on the ACT88760 can be adjusted in 5-mV steps from 0.5 to 1.13 V or adjusted in 20-mV steps to reach up to 3.6 V. Current limits can be adjusted to match with appropriate inductor sizes. A lowering of the current limit can reduce BOM costs by allowing use of inductors that are smaller and which have lower current ratings. Likewise, higher current can be configured when necessary. Such configurability helps avoid last-minute board and BOM changes. It also helps avoid last-minute component changes that can retrigger a certification process.

A final point to note is that MTP NVM can let the same PMIC serve in multiple platforms. This lets inventory be reallocated from one program to another if necessary.

INSIDE A PMIC The ACT88760 is a highly integrated PMIC with seven buck regulators (step-down, switching regulators), six LDOs (low drop out regulators), up to 10 GPIOs, and many built-in system monitors and functions. Of the six LDOs, two can be configured as load switches with a low insertion resistance of 25 mΩ. Three of the buck regulators can support dc output loads up to 4 A; two regulators can support up to 3 A and two others

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support 2 A of load current. Two of the 4-A regulators (Buck1 and Buck2) can operate as a single regulator in two-phase configuration to double the amount of supported load current – up to 8 A. Likewise, Buck3 and Buck4 can work in parallel to double the output current from 3 to 6 A. Buck7 supports 4 A of current, Buck5 and Buck6 support 2 A each. LDO1 and LDO2 support current output up to 800 mA and can accept input voltage as low as 1.2 V. LDOs 3-6 are rated for a maximum output current up to 400 mA . In the load-switch mode, the output is not regulated, and the input is merely passed on to the output to create a power island with an on/off function.

A two-phase buck regulator has several advantages. The ripple voltage and the dynamic transient response can be improved significantly. The two regulators that are combined in two-phase operation have staggered phases, where one clock is 180° out of phase with the other. This phasing effectively doubles the switching frequency and improves the dynamic transient response. Both the output load capability and the optimal efficiency point double. For example, if the best efficiency with a single-phase regulator is with a load current of 1.25 A, the two-phase regulator efficiency point load current is 2.5 A. This feature allows high efficiency even at high load currents. In contrast, a single-phase regulator’s efficiency drops off at higher currents because conduction (resistive) losses increase as the square of the current gain– conduction losses rise by a factor of four when the current doubles. And eeworldonline.com

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PMIC TECHNOLOGY resistive rises with self-heating, typically making efficiency even worse.

A description of GPIO functions helps explain the advantages of configurability. The ACT88760 has up to 10 configurable GPIOs. The On/Off control of the PMIC can be selected from three different functions and modes of operation – a push button function, a PWREN (Power Enable) configuration or a PWRON (Power On) configuration. The push-button functions facilitate features used in consumer devices such as cameras, phones, video devices, point-of-sale portals, smart home pods, etc.

A single push button can turn-on the device, power-off the device or even initiate a hard reset via a press-and-hold.

The PWREN function uses a different power control state machine more suited to SSD drives and other uses where a single pin can control on/off functions and the initiation of low-power states such as DPSLP (Deep Sleep) or SLEEP. The last mode of operation is the PWRON (Power On) function, in which the operating state machine follows the PWRON

input pin as a simple enable signal that can turn on or turn off the PMIC regulators.

Additionally, other GPIOs can be configured as input/output pins in an opendrain configuration or as outputs in CMOS or push-pull configurations. Most GPIOs also include configurable pull-up and pull-down resistors, eliminating the need for external resistors. This feature also provides options for connecting the pull-up resistor to different voltages, such as 1.8 V (I/O voltage) or 5 V (the system voltage, which can also be the same as battery voltage).

GPIOs can perform input functions such as generating an interrupt when the input-signalstatus changes. The input signals from GPIOs can turn on regulators, trigger low-power states such as SLEEP, change regulator output voltages for dynamic voltage scaling, accept power-good signals from external regulators, or even trigger power sequences. GPIOs can also generate outputs such as a system RESET, power-good and fault-status indicators for the PMIC or individual regulators, and low-power

and status indicators. They can as well control external regulators and sequence their on/ off times, provide interrupt requests, drive LEDs (current sink), and many other such functions.

In a nutshell, GPIOs can incorporate many system-level functions and may eliminate the need for house-keeping microcontrollers.

REFERENCES Qorvo, www.qorvo.com

Proven integrity AND industry know-how Electrocube is one of the most respected design manufacturers of passive electrical component products for a wide range of standard and custom applications – from aerospace and audio to elevators and heavy equipment – as a capacitor supplier, resistor-capacitor distributor, and more.

Bishop Electronics, Seacor, Southern Electronics, F-Dyne

ELECTROCUBE.COM | 800.515.1112 | INFO@ELECTROCUBE.COM

POWER & ENERGY EFFICIENCY HANDBOOK

Improvements in stacked load architectures Stacked-load schemes have made power conversion more economical in server racks. New developments in this technology promise to provide additional gains in efficiency.

Laszlo Lipcsei, Alexandr Ikriannikov, Di Yao Maxim Integrated, now part of Analog Devices Load currents continue to rise in server applications while rail voltages tend to drop. Consequently, the conduction losses

STACKED LOAD SCHEME

on the PCB are becoming increasingly harmful . For example, a processor running at 0.8 V and 1,000 A can require 24 phases of voltage regulator power stages to convert from a 12-V input down to the 0.8-V of the processor. The power conversion loss can easily reach or exceed 10%. The voltage regulators often need to sit a few inches away from the MCU such that the I2R loss can become significant as well. And high-current ASIC packages can reach the ball grid array electromigration limit that can either limit the amount of current that can be delivered into the chip package or jeopardize the package reliability.

The concept of stacked power elements and processing of the power difference are considered possible solutions to this problem. Series-stacked architectures reduce the high stepdown voltage conversion ratio in conventional architectures.

Differential power processing converters regulate voltages and compensate for mismatches between MCU currents. In particular, the Energy Exchanger concept looks promising, where only the power difference is processed. In this architecture, the average current is observed in the system rail, not the minimum current of the elements connected in series.

Losses are generally proportional to the processed power, so lowering the processed power usually reduces losses. And

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Block diagram of the stacked load prototype.

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EFFICIENT SERVER SUPPLIES SINGLE-ENDED ENERGY EXCHANGER

PROPOSED DIFFERENTIAL ENERGY EXCHANGER

the Energy Exchanger architecture can use different converters, including different capacitor circuits.

First a brief overview of the stacked power element and energy exchanger concepts. Power balancer circuits enable multiple load zones of an IC to be powered in series while maintaining balanced voltage at each load zone. The power balancer typically includes a dc transformer array consisting of a dc transformer connected in parallel with each load zone and for each load zone, a bus capacitor connected in parallel. Each dc transformer is electrically connected other dc transformers providing an electrical path for each bus capacitor to discharge current to other bus capacitors when a voltage across a bus capacitor exceeds a voltage across another bus capacitor.

Each dc transformer can include a switched capacitor circuit that includes a pair of switches such that when the first switch is on, the second switch is off and vice versa.

A controller turns the switches on and off according to a specified duty cycle. The power balancer can include a voltage regulator for each load zone connected between the bus capacitor for the load zone and an input power connection to the load zone.

We can extend this concept to applications needing aggressive transient management. Voltage Regulators (VRs) are added to deal with the fast transient loads. A prototype board implements the single-ended energy exchanger with switched capacitor circuits. As you might expect, the singleended Energy Exchanger showed significant noise pollution of the load rails when

processing a significant power difference.

Measured system efficiency was ~86% at full load of 250 W, with predicted ~2% improvement if the bias circuits are improved.

Visible in the block diagram of the Stacked Load prototype is the main Voltage Regulator VRR_total which delivers full power to the stacked loads as efficiently as possible. The four fast voltage regulators are responsible for the precise voltage regulation and transient response on each corresponding load rail.

If loads are ideally matched, these fast VRs process zero power. They process a power difference only if there is a load mismatch.

The fast VRs are thermally designed for much smaller current than VRR_total, as the maximum load difference is assumed to be smaller than the full load. However, it is important to design fast VRs so they can handle the full-scale transient of each load. Even if all loads are closely matched on average, it is hard to expect perfectly matched transient steps on all of them, and it takes longer for the slower VRR_total to adjust the output current.

The Energy Exchanger ensures power exchange among all the input rails for fast VR. If VRR_total is driving only linear loads connected in series, the output current is determined by the lowest load current. But when the Energy Exchanger is added, the VRR_total output current ideally becomes averaged current between all loads. In practice, that current is slightly higher as it compensates for the losses in the fast VRRS and Energy Exchanger.

Consider two different designs for the Energy Exchanger: the originally considered single-ended Energy Exchanger and a fully differential Energy Exchanger from.

Simulated performance during the 50-A step in the load RL4. Left, single-ended Energy Exchanger. Right, differential Energy Exchanger.

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POWER & ENERGY EFFICIENCY HANDBOOK Stacked load system prototype. Fast transient loads were used to evaluate the dynamic performance, implemented by pluggable modules (only one plugged module for fast transient is shown in the picture). The main board also has connectors for the fast VRs. This arrangement allows easy adjustment and changes to the fast VR modules.

The single-ended Energy Exchanger has a problem: Return currents from each flying capacitor must go through the Co bulk capacitors of the loads in series. These charge-discharge currents have a much faster ac content compared to the output currents of the buck converters (both VRR_total and fast VRRS). The simulated system performance with the single-ended Exchanger, when the load RL4 has a current step of 50 A, shows noise on all rails in general, which significantly rises when the Energy Exchanger starts moving charge to the input of VRR_4. The differential Energy Exchanger does not force any currents through the loads or the Co bypass of the load rails, fixing the noise problem.

Two prototypes for the stacked load system

were designed with the only difference being in the Energy Exchanger: one design contained the singleended version, the second the differential Exchanger.

Fast transient loads were used to evaluate the dynamic performance, implemented by pluggable modules.

MEASURED RESULTS

With load voltages at 0.8, 0.9, and 1.0 V, the two different Energy Exchanger options have nearly the same efficiency. In the nominal operating conditions, Vo = 4 x 0.9 V = 3.6 V reaches more than 95% at full load. Note that placing all loads in parallel corresponds to 500 A current into a single Vo = 0.9 V rail. Achieved >95% system efficiency noticeably outperforms published efficiency data for these conditions. Two main factors account for the high efficiency: 4x output current reduction as four loads are connected in series, and the main VRR_total delivers full power into 4x higher Vstack voltage (4 x Vo), as higher Vo generally improves VRR efficiency.

This is a prototype board with off-the-shelf parts and no optimized components; high efficiency is in part due to coupled inductors used in the main VRR_total, as well as fast VRR modules. Generally, coupled inductors keep switching frequencies low in a given reasonable size, keeping the switching loss down. This is especially important for the fast VRRS, because in the case of balanced loads, these VRRS do not process much power but still have switching Measured system efficiency of the complete system operating losses that ideally should be with a balanced load, including all the bias circuitry from minimized.

12-V input and control, with two different Energy Exchangers The big difference (single-ended and differential) for the different Vo rails. in the operation of the two different Energy

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Voltage ripple on V01 (>60 mV) and floating Vin1 (>300 mV) for the system with a single-ended Energy Exchanger.

Voltage ripple on V01 (~25 mV) and floating Vin1 (~70 mV) for the system with the proposed differential Energy Exchanger.

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EFFICIENT SERVER SUPPLIES

Fast transient performance with (left) loading and (right) unloading 100-A steps on rail Vo1.

The other rails are unloaded.

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Exchangers is in voltage ripple on all the first Vo1 rail and VR1 input supply rails. The Vo4 rail is loaded by I0 = 50 A, and all other rails are at zero current. So the Energy Exchanger is moving a lot of power from the other rails to supply the Vo4 rail. The single-ended Energy Exchanger drives large spikes through the parasitics of Co on the Vo1 rail while the differential Energy Exchanger just leaves the Vo rail intact, with only a small ripple at much slower time scale that relates to the buck converter currents (not the switched capacitor circuits).

The most important impact is the reduction of the fast voltage spikes from >60 mV (>6.6% of Vo = 0.9 V) in case of the single-ended Energy Exchanger to <25 mV (<2.8% of Vo = 0.9 V) in the case of the differential version. In the latter case, the voltage ripple has no high-frequency spikes at all, only a ripple associated with the ripple current in the buck converters. The result matches the expected trend from the simulations. The fast spikes on the supply rail can potentially harm the digital circuitry, and it is important to mitigate the issue. As Vo values are expected to drop further, the same amplitude of the noise has a larger impact on the operation of the fast loads.

Noise in the differential Energy Exchanger can also be reduced by phaseshifting among switching events for the different flying capacitors. Notice this tactic is not possible for the single-ended circuit; all capacitors must be switched at the same times.

Fast transient performance is shown in the nearby figure for loading and unloading 100-A steps on rail Vo1. The other rails are unloaded. So, while initially the fast VRR1 delivers all 100 A, the averaged 25 A comes from the VRR-total and the fast VR1 supplies only 75 A to the 100-A load. Looking at the changing droop on the Vo1 rail, note that it takes approximately 10 µsec for the VRR-total to deliver 25 A average current, which reduces the fast VR1 droop proportionally.

Correspondingly, VRR2, VRR3, and VRR4 subtract 25 A from their rails and move that power into the Energy Exchanger and VRR1. The Energy Exchanger voltages are unregulated. So, it takes longer than 10 µsec to settle the input rail for the fast VRR1 (yellow trace).

In a nutshell, a fully functional

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Stacked Load prototype showed efficiency generally higher than in traditional architectures for the same Vo and total Po (>95% at Vo = 0.9 V at Po = 450 W).

The prototype employed off-the-shelf components; optimizations can potentially lead to even higher performance.

The concept of stacked load power delivery shows good promise in improving efficiency, as distribution losses dramatically drop and the main VR operates at higher efficiency because of higher load-voltage Vstack. Notice also that the significant drop in load current should reduce PCB losses when the loads are densely packed. In other words, real applications with dense high-current and low-voltage loads have bigger challenges in distribution losses. So, improvements via stacked-load architectures can be higher than on some prototype board.

Building on the earlier Energy Exchanger concepts, the differential Energy Exchanger for floating rails reduced noise for the load voltage rails as any fast current and related voltage spikes were eliminated in any kind of loading.

REFERENCES Maxim Integrated, now part of Analog Devices, www.maximintegrated.com A. Ikriannikov and A. Stratakos, “System, method, module, and energy exchanger for optimizing output of series-connected photovoltaic and electrochemical devices” U.S. Patent 9,331,499, filed April 2011.

E. Candan, P. Shenoy, and R. PilawaPodgurski, “A Series Stacked Power Delivery Architecture with Isolated Differential Power Conversion for Data Centers” in IEEE Transactions on Power Electronics, vol. 31, No. 5, May 2016.

S. Jiang; G. Sizikov; M. Popovich, “Power balancer for series-connected load zones of an integrated circuit,” U.S. Patent 10,985,652, filed March 2020.

K. Kshirsagar, D. Clavette, P. Kasturi and W. Huang, “Power Loss Reduction in Power Distribution Network Through Vertical Stacking,” Industry Session in IEEE 2021 Applied Power Electronics Conference, June 2021.

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POWER & ENERGY EFFICIENCY HANDBOOK

The evolution of smart MOSFET technologies A review of MOSFET advances helps predict where the technology is likely to head.

Ashita Mirchandani, Bastian Lang • Infineon Technologies

The past 50 years have seen unprecedented changes enabled by technology. The trend will continue with emerging technologies such as e-mobility, the Internet of Things (IoT), artificial intelligence, connectivity and 5G. At the heart of these emerging technologies is cuttingedge innovation in MOSFET technologies that provide power.

These new application areas are increasingly power hungry, challenging MOSFET designers to adapt new power architectures and higher bus voltages. There’s also a need to deliver power more efficiently in eversmaller form factors. For example, today’s smart phones provide many more features than cell phones from years past but in a comparably sized package.

When faced with these new challenges,

designers must keep the customer’s end application in mind. Evaluation should incorporate test conditions identical to those in the environment where the device is to be used. In these cutting-edge applications, use of the right power switches often determines system performance.

Innovations in MOSFET technology that handle emerging applications are not a new phenomenon. Consider the first hexagonal topology MOSFETs in 1979, known also as HEXFET. This technology enabled the rapid commercialization of switch-mode power supplies. Similarly, a new MOSFET technology in 1995 was based on an advanced four-mask process using innovative self-alignment features to improve manufacturing precision and yields.

It lowered MOSFET manufacturing cycle time and allowed junction depths up to 40% shallower than before, reducing the transistor junction resistance while boosting ruggedness. Shortly

THE DRAIN-DOWN INDUSTRY STANDARD

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afterwards, the first FETKY was introduced.

(Basically, a co packaged HEXFET and Schottky diode). The single silicon FETKY chip reduced the form factor and losses in dc-dc applications.

In 1999, a stripe planar technology was perfected that featured an extremely low on-resistance, excellent high-frequency operation, ruggedness and low manufacturing cycle time. The same year, a family of Trench power MOSFETs enabled industry’s highest cell density and lowest RDSon. This technology focused on delivering high energy efficiency for handsets, laptops and other portable electronic devices.

The year 2000 brought the first family of OptiMOS MOSFET technology featuring ultraA comparison of the internal construction of a standard Drain-Down device and the new Source-Down device.

THE SOURCE-DOWN INNOVATION

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SMART MOSFETS

HSC TOPOLOGY

The HSC is formed by six MOSFETs divided into two legs, connected through two flying capacitors and a magnetic device called a multi-tapped autotransformer (MTA). The MTA is formed from four windings connected in series sharing the same magnetic core. High-frequency operation is enabled by ZVS operation with the magnetizing inductance of the MTA.

low switching losses for high efficiency. The OptiMOS family is now in its sixth generation, with each family further reducing RDSon and improving switching performance. Applications such as synchronous rectification in switched-mode power supplies (SMPS) for servers, desktop PCs, wireless chargers, quick chargers and OR-ing circuits now use the technology.

In 2021 came the StrongIRFET family. These MOSFETs are optimized for low RDSon and high current, making them candidates for low-frequency applications requiring ruggedness such as cordless power tools, light electric vehicles and e-bikes.

Packaging is also an important aspect of power products. In 1993, the SOT-223 was introduced as the first surface-mount power MOSFET. In 2002 came the DirectFET power package, a proprietary surfacemount format with a new interconnection methodology bringing radical gains in both conduction and thermal efficiencies. The widely used TO-Leadless package came in 2013. It handles high current in a reduced foot-print compared to a traditional D2PAK. Most recently, Infineon has devised a family of OptiMOS power MOSFET devices in a PQFN 3.3x3.3 Source-Down package (the IQE006NE2LM5) with a flipped die for better thermal performance and lower RDSon.

multi-tapped autotransformer (MTA). The MTA is formed from four windings connected in series sharing the same magnetic core.

High-frequency operation is enabled by ZVS (zero-voltage switch) operation with the magnetizing inductance of the MTA. The HSC provides an unregulated voltage rail which depends on the turns ratio between the MTA primary windings N1 and N2. The topology is driven by two symmetrical PWMs dubbed H (i.e., Q1, Q3 and Q5 are ON with Q2, Q4 and Q6 OFF in the nearby topology diagram) and L (i.e., Q1, Q3 and Q5 are OFF with Q2, Q4 and Q6 ON). An introduced dead-time between the states enables load-independent ZVS operation. The HSC can run aboveand below-resonant frequency without influencing the ZVS operation. Therefore, the overall system performance can be kept at a high level regardless of component tolerances.

One of the key enablers for high efficiency and high power density of the HSC is the use of low-voltage rated MOSFETs with better figure-of-merits (FOMs). For example, in an 8:1 configuration running from a 48-V rail, 25 V-rated MOSFETs for Q3 and Q6 can be used.

Combined with new Source-Down products, the HSC can provide the power density needed in modern data centers. Main benefits of the package include 30% lower RDSon, lower package-related parasitics and lower Rthjc. As the thermal pad is located on the source pin, the package Q3, Q6: 4 X BSZ011NE2LS5I

Q3, Q6: 4 X IQE006NE2LM5

FUTURE DEVELOPMENTS Innovations in power delivery and packaging continue to enable new applications. Consider artificial intelligence. Power management– more specifically, the energy density of the power converters fueling processors and ASICs–is a big challenge for designers. The introduction of 48-V bus voltage allows additional power conversion close to the payload to avoid transmission losses.

With Infineon’s Hybrid Switched Capacitor (HSC) resonant dc-dc converter, innovative components brings new capabilities to the whole system. The HSC is formed by six MOSFETs divided into two legs, connected through two flying capacitors and a magnetic device called a

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The thermal behavior of the HSC at 450 W from a 48-V input at Tamb = 24°C and v = 3.3 m/sec. On the left is the performance with the Drain-Down device (BSZ011NE2LS5I).

At right, with the Source-Down device (IQE006NE2LM5).

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Passive Component

Power Solutions

POWER & ENERGY EFFICIENCY HANDBOOK

EFFICIENCY DATA

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BGRV, BWRV, BSRV Up to 40W

The HSC converter efficiency from 48 to 6 V, including auxiliary losses, with the BSZ011NE2LS5I and with the IQE006NE2LM5 at Tamb = 24 °C and v= 3.3 m/sec.

High-Voltage Thick Film Resistors HV73 Up to 3,000VDC

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Surge Current Flat Chip SG73 0.1-1W Ultra Precision Flat Chip SG73G 0.2-0.5W Endured Pulse Power SG73P 0.125-1W Endured Surge Voltage SG73S 0.125-1W

enables optimized layouts where the large GND area can be used as a heatsink.

The performance benefits can be visualized from the comparison of two 8:1 HSC converter boards. One is based on a standard Drain-Down device (BSZ011NE2LS5I) and the other on the new Source-Down device. A hotspot can be observed in the traditional package but not in the new Source-Down package. The surface temperature of the MOSFET is significantly lower, showing a 9°C difference compared to the Drain-Down device. The higher efficiency of the system incorporating the Source-Down device leads to a significant increase in power density as well.

The development of MOSFETs and packaging will continue to evolve. MOSFET technology continues to power emerging technologies through new innovations. While there is tremendous potential for wide bandgap (WBG) devices such as SiC and GaN, silicon is still the mainstream choice for many applications. Silicon and WBG materials will both play a role in power switching. New innovative MOSFETs power the latest applications and continue to be “cool.”

REFERENCES Infineon Technologies, www.infineon.com

To learn more about KOA Speer’s Power Solutions, visit KOASpeer.com

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Sorensen™ Asterion® DC ASA Series Multiple-Output Programmable Power Supply with Touch Screen Display

The Sorensen™ Asterion® DC ASA Series is the newest addition to the Asterion platform of power testing solutions. The new ASA Series features up to three independent, isolated, extended wide-range outputs in a 1U high chassis. The autoranging supplies feature expanded current and voltage range at the full output power level, enabling the ability to satisfy a wider testing need without requiring the purchase of additional models.

AMETEK Programmable Power designs, manufactures, and markets precision AC and DC programmable power supplies, electronic loads, application-specific power subsystems, and compliance test solutions.

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POWER & ENERGY EFFICIENCY HANDBOOK

Identifying the right medical power supply Special considerations apply for power supplies when even small electrical currents pose a shock hazard.

Dermot Flynn, Chris Jones • Advanced Energy The consequences of leakage current came to the forefront in the 1970s, and since then technical standards for the safety and effectiveness of medical electrical equipment have evolved to become the most stringent of any industry. Defined as the flow of electric current in an unwanted conductive path under normal operating conditions, leakage current is a direct function of the line-to-ground capacitance value. As long as equipment is grounded, these currents will flow in the ground circuit and present no hazard. However, if the ground circuit is faulty, the current flows through other paths such as the human body.

Over the years, researchers have discovered that as little as 3 µA (0.000003 A) applied directly to a portion of the heart during a critical part of the cardiac cycle could cause lethal arrhythmia. To ensure patient safety, the International Electrotechnical Commission (IEC) created two main standards for power supplies including IEC 609501 for ITE (information technology equipment) and IEC 60601-1 for medical equipment.

Both standards protect against electrical shock, but as medical equipment may come into contact with a patient, IEC 60601-1 requires a higher level of safety.

The classification of medical equipment for protection from electric shock is as follows: Class I: Reliable protective earth is provided such that all metal parts cannot become live in case of insulation failure (three-pronged ac plug – live, neutral and electrical ground).

Class II: No protective earth. Double or reinforced insulation is used against electric shock (two-pronged ac plug – live and neutral only).

Class I or II when external power source is used. Classification does not apply if internally powered by battery.

Protective earth: Ground conductor in the Key differences between the power cord, also known as chassis ground.

ITE and IEC safety standards

Subjects

IECC 60601-1

Creepage distance/ clearance distance

Basic insulation

2.5 mm/2 mm

4 mm/2.5 mm

Working voltage: Max. 250 Vrms

Supplementary insulation

5 mm/4 mm

8 mm/5 mm

Electric strength test

Basic insulation

1500 Vac

1500 Vac

Supplementary insulation

3000 Vac

4000 Vac

Class I

Handheld: 075 mA

--

Others: 3.5 mA

Leakage current of grounding

0.3 mA

Leakage current of case

0.3 mA

Leakage current of case

0.1 mA

Leakage current

Class II

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IEC 60950-1

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0.25 mA

10 • 2021

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MEDICAL POWER SUPPLIES EMBEDDED POWER Advantage

Disadvantage

Available in higher power ranges

End-product requires full safety and EMI approvals

Allows for multple voltages without additional post DC-DC regulators

Requires larger physical space inside end-product

Single power cord minimizing external clutter

Power supply heat and EMI inside end-product

Additional criteria within IEC 60601-1 defines three distinct categories requiring protection against electrical shock from an applied part (any part of the electrical medical equipment that comes into contact with a patient): Type B = “Body” – Sometimes considered “patient vicinity.” No electrical contact with the patient and usually earth-grounded. Type B is the least stringent classification and is used for applied parts that are normally not conductive such as LED lighting, medical lasers, MRI body scanners, hospital beds and phototherapy equipment.

BF = “Body Floating” – More stringent than Type B but less stringent than CF, it is generally used for applied parts that have conductive contact with the patient but not directly to the heart. Examples are blood pressure monitors, incubators and ultrasound equipment.

CF = “Cardiac Floating” – Electrically connected to the heart of the patient, CF is the most stringent classification. It is used for applied parts that may come in direct contact with the heart, such as a dialysis machine.

Research in the medical field is accelerating, and the resulting advanced devices require advanced power conversion technology that also meets safety regulations.

Choosing a power supply for a medical product, however, is no easy task. In addition, it is critical to determine if a standard “offthe-shelf” medical power supply or a custom medical power supply can meet the specific application requirements.

CUSTOM VS. STANDARD Custom designs have many advantages including providing exactly the power needed for a specific application. On the flipside, there is development cost, non-recurring engineering (NRE) fees, and a development time typically spanning 8-12 months. The supply is also single-sourced unless another vendor is paid again for development.

The advantages of standard medical

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power supplies include the wide variety in industry standard voltages and packaging, immediate availability and safety preapproval. They can also be modified by many manufacturers and distributors, and are more readily available from a supply chain perspective. In addition, there is no upfront cost for NRE or safety. However, COTS power supplies may not be ideal for medical products as they offer limited control over modifications and the lifecycle of the power supply. For multiple outputs, configurable power supplies offer great flexibility with millions of output voltage combinations with safety approvals.

Most medical equipment designs have multiple components with differing power needs, so designers often use a distributed power architecture. If a product requires lowpower ac-dc, there are often options between a power supply embedded in the end-product or an external unit such as an adapter. In addition, many medical instruments, including mass spectrometers and scanning electron microscopes, need high-voltage dc sources. So it is important to look at power from an overall system perspective. Devices that require medium or high-power ac-dc, consider the following questions: Is it offered in single-and three-phase input?

Is it available with or without intelligence?

Is it generally enclosed with fan cooling?

Fan cooling in particular is an important consideration. In medical applications having acoustic and vibration sensitivity, fanless power supplies offer advantages. Cooling is via the natural flow of air (passive natural convection) or the transfer the heat through direct contact with a cooler component (passive conduction).

Passive natural convection in power supplies usually involves an open-air rack, where the natural movement of air across electronic components removes some excess heat.

Passive conduction was once only possible with the most basic power supplies. But advances

10 • 2021

Decision making chart for low power standard medical power supply

in thermal modeling, component design/ selection and materials technology now enable high-performance units to be cooled without using fans.

Electromagnetic compatibility (EMC) is also critical in power supply design and selection.

EMC requirements for medical electrical (ME) equipment and ME systems are stated in IEC 60601-1-2, a collateral standard to IEC 606011. Under this medical EMC standard, power supplies are classified as “non-Medical Electrical (ME) equipment” and therefore are technically required to comply only with IEC EMC standards applying to that equipment (e.g., ITE immunity standard EN 55024), provided the power supply will not result in the loss of basic safety or essential performance of the ME system in its intended environment. Essential performance is determined by the ME system manufacturer.

Given that there are no specified performance criteria for the non-ME equipment itself, the ME system manufacturer should determine whether the EMC performance of a given power supply is adequate for the specified application.

DIGITAL CONTROL Digital control now comprises the feedback loop for many power supplies, via communications channels such as I2C and PMBus, taking the place of older, analog feedback control. Advantages of digital control include reduced parts count, greater flexibility and improved productivity. During development, power supply design bugs can be fixed by firmware patches, eliminating multiple PCB re-spins. In addition, firmware and software can be upgraded in the field via the internet without physically attending the system, and modular code can be reused.

Digital power supplies contain a history log that enables backtracking of failures with failure modes including PMBus/IPMM-defined events such as over voltage (OVP) and over

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39

POWER & ENERGY EFFICIENCY HANDBOOK ADVANCED ENERGY’S UNIVERSAL PMBus GUI

An example of a modern power supply GUI: Advanced Energy’s Universal PMBus GUI.

current (OCP). To assist in field failure analysis, additional events can be recorded such as the runtime of the power supply (power-on-hours), the actual maximum load, the actual maximum ambient, and the actual maximum input.

Digital control also enables the use of a graphical user interface (GUI) as an aid to engineers.

It is a visual tool for debugging and modifying power supply issues such as input thresholds, output settings, delay times, switching frequency, loop response and other parameters. A universal PMBus GUI also enables enhanced power management features, including: Monitoring and reporting power supply input parameters such as voltage, current, and power; self-diagnosis for potential failures or weakened parts by monitoring and comparing specific parameters against nominal values; event logging of conditions such as input voltage surge and sag, ac recycles, maximum ambient/internal temperatures, and failure logging to backtrack failures; fan speed optimization based on load and ambient temperature.

All in all, significant progress in the past few

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DESIGN WORLD — EE NETWORK

years has equipped the medical industry with smaller, more reliable power supplies that reduce cost, complexity and human error. Looking beyond the volts, amps and safety approvals, it is also critical to find a vendor of medical-grade power supplies that will be a trusted partner for many years to come.

REFERENCES Advanced Energy, www. advancedenergy.com

10 • 2021

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POWER & ENERGY EFFICIENCY HANDBOOK

Clearing up confusion about tracking multiple current levels Multichannel power monitors help simplify battery-based systems employing multiple current sensors.

Mitch Polonsky • Microchip Technology Inc.

Designers of power systems can be forgiven for having some confusion about power monitors.

Some of them may even be using a multichannel power monitor without knowing it. That’s because, regrettably, several different phrases are used to refer to this device category. Some designers know them as high-side current sensors, some as current sensors, and some know them as power monitor ICs. The devices being referenced have a digital interface; inputs can be connected directly to voltage rails above 5 V, and will measure current, voltage, and power across a sense resistor.

These power monitors provide the ability to connect to higher voltages. Some power monitors

can accept voltages as high as 100 V, while other mid-range devices can only accept up to 32 V. As such, the devices help avoid external components needed for high voltage applications.

ADI (now including Maxim and Linear Technology), Texas Instruments, Renesas (now including Intersil), and Microchip all have devices in this category. Under Maxim these devices are known as current sensors with digital outputs. However, the ADI website calls these devices power monitors. The consistency of nomenclature continues with both TI and Microchip calling these devices current/voltage/power monitors.

If the system only consists of 5 V, simple operational amplifiers and resistors may be all that is required to measure the system power. Periodic polling could be implemented to lower system power associated with the monitoring. However, this simple scheme does not address the issue of critical power rails that need more active management. Active management may be necessary to measure and optimize power efficiency or to understand the remaining battery life.

It might seem as though an always-on processor would be necessary to do the monitoring. But a host processor that does the monitoring could also reside in a low-power state for much of the time, only waking if an independent current sensor with limits sends an interrupt.

Many host processors need protection components if they connect to voltage rails higher than 5 V, which brings us to an advantage associated with high-side current sensors.

A block diagram of a typical power monitoring scheme.

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DESIGN WORLD — EE NETWORK

10 • 2021

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|

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MULTI-CHANNEL POWER MONITORS First consider only high-side current sensors that are analog. They are offered in commonmode voltages up to 100 V. These devices can connect directly to the higher voltage rails and avoid the need for external protection components. In addition, the devices send the host controller signals representing the current and power in the system.

It should also be noted that analog current sensors come in options with multiple channels. The power that multiple-channel sensors dissipate is normally in line with that of a single device multiplied by the number of channels. For example, a single-channel analog current sensor such as the INA290 has a maximum quiescent current of 600 µA. The dual version in the same family, the INA2290, has 1,200 µA of quiescent current for the same operating conditions.

POWER MONITOR ICs This brings us to the topic of the power monitoring IC, which is a mixed-signal device.

These ICs are improvements on systems employing an always-on host controller and analog current sensors.

Power monitors calculate power consumption on-chip independently of the host controller. The methods used are the same as that of an analog current sense amplifier.

But the power monitor IC goes further by incorporating an integrated ADC and multiplier to produce a digital representation of the power consumption. This digital value can then be made available in a register over a digital interface, thus providing a digital power calculation. As a result, there is a savings in software overhead, development time, and code complexity in the host processor. The host can also spend less time in the awake state while the power sensor accumulates data.

An ancillary benefit is that the power monitor reduces pin requirements on the host via a shared communication bus. Many generalpurpose sensors include shared interfaces for communication with additional power monitors, temperature sensors, memory and more. The same cannot be said for analog current sensors, which require additional pins on the host. Also, shared communication interfaces free up GPIOs for general-purpose use.

Additionally, power monitors conserve host

power by allowing the system to wait for an alert rather than poll for a reading. While waiting, the host can choose to stay in a lower-power sleep or standby state while the power monitor supervises critical voltage rails for excursions.

Now consider multichannel power monitors. What sets multichannel power monitors apart from single-channel devices is the ability create a round-robin sampling and reporting architecture that consumes less system power. Most companies use similar architectures, so we will share the Microchip architecture for the PAC1954 to relay the point.

Note that the PAC1954 device has a single ADC for measuring Vsense. This functional block is multiplexed to measure and report the Vsense voltage from four sense resistors. As a result, it takes less quiescent power to run this architecture then for four separate current sensors.

For example, consider the maximum quiescent current from a competing fourchannel current sensor compared to a highquality single-channel power monitor. We can see the inherent benefit of using one ADC for a four-channel device. The competitive device

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POWER & ENERGY EFFICIENCY HANDBOOK PAC195X-1 FUNCTIONAL BLOCK DIAGRAM

consumes 450 µA max at 85°C for each of four channels of measurement and 16 bits of resolution.

In contrast, the power monitor consumes 400 µA max for 16 bits of resolution and only one channel of measurement, or 1,600 µA. The same calculation can be performed with the latest Microchip device. Consider a dual power monitor, the PAC1952, with a maximum quiescent current of 495 µA at 125°C. Compared to competing devices at 800 µA, there is a systems power savings of 1 – (495/800) = 38% with respect to the power measurement.

Thus the many reasons to use a multichannel power monitor IC include: Saving software overhead, development time, and code complexity Saving time in the awake state, while the sensor accumulates data Reducing pin count on the host or freeing up host pins for more GPIOs Saving host power by using alerts to wake the system rather than poll for a readings for excursions

44

DESIGN WORLD — EE NETWORK

All in all, there is a measurable power savings associated with the use of multichannel power monitors in lieu of single-channel monitors. An architecture based on a shared ADC will facilitate a savings of up to 38% of the power associated with the monitoring of the system voltage rails.

REFERENCES Microchip Technology Inc., www.microchip.com

10 • 2021

The PAC1954 device has a single ADC for measuring Vsense. This functional block is multiplexed to measure and report the Vsense voltage from four sense resistors in the system. As a result, less quiescent power is required for this architecture than for four separate current sensors.

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POWER & ENERGY EFFICIENCY HANDBOOK

Gains from GaN Energy efficiencies made possible by gallium-nitride semiconductors are starting to impact every day products.

Paul Wiener • GaN Systems, Inc. | Ron Stull • CUI, Inc.

Wide-bandgap power semiconductors are

The typical technology adoption cycle.

in production now and recommended for new designs. The earliest adopters among power supply OEMs have already begun introducing new product lines employing this technology to deliver smaller size, greater efficiency, and more power than their predecessors.

As ordinary silicon-based power reaches the end of its roadmap, it’s time for power supply specifiers to change gear.

Silicon-based semiconductors, from processors to power transistors, have enabled tremendous advances in the way the world lives and works.

From the invention of the p-n junction in the 1930s-40s through the periods of exponential progress highlighted by observations such as Moore’s Law, the electronics industry has become the global phenomenon it is today, largely built on silicon.

We know, however, that as a technology matures, the gains from each iteration diminish while it takes more effort to realize them. Then, typically, a new technology arrives and changes the game. There is a leap forward followed by a period of rapid progress.

Commercially, these technological singularities can be dangerous for market leaders. At times of disruption, new upstarts can quickly eclipse those intent on wringing the last few drops of potential from the old ways.

This sort of event is happening right now in power conversion. A new generation of power supplies and converters is arriving based not on silicon devices but instead on newer wide-bandgap power semiconductors. Among these, gallium-nitride (GaN) power transistors now enable significant advances in power density, efficiency, and thermal performance when the need is for breakdown voltages up to about 600 V.

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DESIGN WORLD — EE NETWORK

Switched-mode power supplies designed with GaN devices can operate efficiently at a switching frequency higher than is workable with ordinary silicon components. The efficiency gain is so great that the PSU can operate at the full rated power with only a small heatsink or, sometimes, no heatsink at all. Also, the higher frequency allows smaller magnetic components and capacitors to condition the power supply output. Overall, a GaN PSU can be half the size or smaller than a comparable silicon-based design.

10 • 2021

These space savings are important for organizations that buy power supplies. For example, consider internal power supplies.

These are often the last item to be considered in the design of a new product. There can be problems if commercial supplies don’t fit the space left over after the main design work has been done. Being inherently smaller, GaNbased PSUs can help alleviate such issues.

The form factor of a GaN-based adapter compared to a silicon-based adapter (dashed line) of same power level.

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GAN POWER SUPPLIES

Data centers, displays, laptops, and audio applications all benefit from GaN based power supplies.

GaN-based external adapters, on the other hand, can be half the size or less of conventional units. The smaller size gives consumers the chance to declutter their environment. For example, imagine the effect in a commercial gym that has row upon row of exercise machines. CUI has recently introduced a family of GaN-based power adapters in a technical collaboration with GaN Systems. Units are available off the shelf in various popular power ratings up to 160 W and further models are planned.

OEMs choosing the new GaN adapters can instantly get a competitive advantage over similar products based on ordinary silicon. Moreover, GaN’s efficiency advantage helps ensure the environmental performance that is both mandated by legislators and demanded by markets.

GaN power semiconductors are driving improvements in numerous industries. In automotive applications, for example, size reductions in power-conversion circuitry allows what was formerly dead space within a vehicle to become usable. Suddenly, ECUs or modules can squeeze into previously impossible positions and enable extra value-added features or facilitate exterior styling that ushers in a sleek new look.

Sleekness also helps win the hearts of gamers. The thinnest laptops are prestige items, and ambitious GaN designs dramatically cut the vertical height of the computer power supply to make possible dramatic low profiles. In television design as well, thin is “in.” Power supplies using GaN transistors have helped realize ultra-low-profile designs that make the most of extremely thin display technologies such as OLEDs. Another application is in data center server blades where GaN technology has made it possible to shrink on-board power modules to about 30% of the accepted normal size. A typical conventional power

module measures 185x70 mm and one blade typically requires two of them. GaN thus liberates the board space occupied by more than one entire module.

Numerous other applications can benefit from the size reduction and efficiency made possible by GaN power semiconductors. Examples include mobile chargers, ac/dc power supplies and inverters for energy storage and power conditioning, blockchain processing, powered hospital beds, drives for autonomous guided vehicles, e-mobility systems, and others.

Additionally, GaN is enabling new switching-circuit applications not feasible using conventional silicon transistors. These include aircraft wing de-icing, making use of GaN transistors’ ability to switch efficiently at extremely high frequencies; and high-quality class-D audio amplifiers that take advantage of extremely fast and clean GaN switching transitions to create close-to-perfect square waves that permit simplified filtering with reduced distortion.

GaN now enables leading electronics brands to make a leap. Product designers and specifiers can take advantage of the emerging generation of high-efficiency power supplies and adapters to trim dimensions, boost performance, and save energy as well as explore new applications.

REFERENCES GaN Systems, Inc., www.gansystems.com CUI, Inc., www.cui.com

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