EEWeb Pulse - Volume 58

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Issue 58 August 7, 2012

Bill Hall Senior Vice President ON Semiconductor

Electrical Engineering Community

Experts Exchanging Ideas Every Day. VISIT DIGIKEY.COM/TECHXCHANGE TODAY! Digi-Key is an authorized distributor for all supplier partners. New products added daily. Š 2012 Digi-Key Corporation, 701 Brooks Ave. South, Thief River Falls, MN 56701, USA

TA B L E O F C O N T E N T S TABLE OF CONTENTS

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Bill Hall ON SEMICONDUCTOR Interview with Bill Hall - Senior Vice President & General Manager of the Standard Products Group

9

Featured Products Digital Power Solutions Offer Performance Integration Enhancement and

11

BY ALEXEI ZERNOV, YNGVE WERNQVIST & CHRIS YOUNG WITH INTERSIL Why digital power solutions are becoming more widespread for their advantages in power conversion and efficiency.

Using Analog Components to Manage Power in Low-Power Solar Systems

16

BY MARTIN TOMASZ WITH TOUCHSTONE SEMICONDUCTOR

How analog op amps support “always-on” circuitry around the microcontroller offering the best low-power solution.

RTZ - Return to Zero Comic

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INTERVIEW FEATURED INTERVIEW

Bill Hall

ON Semiconductor

How did you get into electrical engineering and when did you start?

I actually got my start by mowing the lawn at an electronics distributor when I was in high school in the early 70’s. I was eventually offered a parttime job in the warehouse. When I graduated from high school, the manager of the warehouse offered me a full time job at $135/wk. Since I had no idea what I wanted to do in life, I took the job with the goal of working my way into sales. After 2 years of being told I was more

valuable in the warehouse then in sales, I decided it was time to go to college. During my time at the distributor, I had contact with many Electrical Engineers. They seemed really smart and drove nice cars and since I was good at math, I decided to become an Electrical Engineer.

In addition to starting college in 1975, I also got married, which meant I needed a source of income.

I decided to pick Drexel University in Philadelphia because they were one of the few schools in the country

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at that time with a Co-op program.

This allowed me to work full-time 6 months of the year while getting a BSEE. I co-op’d at RCA Missile and Surface Radar Division and got to do cool things like write software for a missile flight simulator along with some mundane jobs like peeling Rubylith. I eventually graduated from Drexel in 1980 and took a full time job with RCA.

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INTERVIEW

I was hired as an applications engineer, but on my 1st day of work, my boss asked if I would be willing to be a marketing engineer for 3 months then I could go back to applications engineering. I said, “if the pay is the same, no problem” even though I had no idea what marketing did. I actually found that I liked marketing because you got to make a lot of strategic decisions. So after 3 months, I stayed in marketing

and began to climb the ladder, working through various manager positions. Marketing exposed me to many aspects of the business, but the next step I wanted was to run a business. In 1987 Fairchild was sold to National and I took

In the near future, we can expect to see wide band gap technologies, much more use of integrated passive components in filtering, oscillators and RF amplification.

Also, advances in chip singulation will increase the number of die per wafer without changing lithography. on several Product Line Director positions. I liked running product lines because you were essentially running a small company within a larger company. In these positions I was responsible for marketing, product development, design, product engineering, applications engineering, supply chain, and all the financial aspects of the P&L. It was real easy to tell if you were

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doing a good or bad job, just look at the P&L. National Semiconductor spun off Fairchild in 1997 and I stayed with Fairchild, so I worked for 3 companies in the space of 10 years and never changed my phone number. I kept getting more and more product lines folded into my group and got promoted to Vice President of the Interface & Logic Group in 1999 and eventually created and co-ran the Standard Products Group in 2004.

In 2006 I moved from Fairchild in Maine to ON Semiconductor in Phoenix as Senior VP & GM of the Standard Products group. As they say; it’s a dry heat.

What have been some of your influences that have helped you get to where you are today?

My father instilled a good set of values and a good work ethic in me.

The warehouse manager that I worked for taught me not to worry about what other people are doing just focus on doing the best job you can and cream always rises to the top.

Do you have any tricks up your sleeve?

Somebody once told me that if you are an engineer, you can do almost any job that is out there, which has worked for me. In my career, I have been a radar design engineer, a semiconductor applications engineer, a marketing engineer, a product engineer, and have had management jobs with finance, quality, HR, supply chain and

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FEATURED INTERVIEW

Can you tell us more about your work experience before you started at ON Semiconductor?

My first job was with RCA as a RADAR Design Engineer. I worked on a RADAR digital signal processor for 5 years. We began by designing the system on paper, pretty much using discrete Logic IC’s along with some EEPROMs and some bit slice micro-processors. The design was at the module level, so, for example, one module was a complex arithmetic multiplier, another was a target detector and so on. This was cool stuff because we actually used mathematics that you thought were just in textbooks, like real and imaginary numbers, Euler’s Theorem, and RADAR countermeasures techniques.

After the design was complete, we simulated the modules in FORTRAN and eventually manufactured the modules and began test and integration. Test and integration lasted years and involved rotating shift work since these modules were installed in a commissioned navy ship (actually just a conning tower) in the middle of a corn field in New Jersey. Eventually, the changing shifts got old and I went to work for Fairchild Semiconductor in Maine.

INTERVIEW

What has been your favorite project that you’ve worked on?

My favorite engineering project was designing anti-counter measures hardware for a naval radar. I had to implement algorithms in hardware for target detection in a jamming environment, or detecting a target in cloud cover, or telling a target from a fake pulse that the target broadcasts back to you. It’s a very creative process and these modules that you design are like children.

Do you have any note-worthy engineering experiences?

One experience that stands out was when I first moved to Fairchild in 1985 and became the Marketing Manager for ACMOS Logic. We were launching the FACT family (Fairchild Advanced CMOS Technology). A large competitor in Texas who shall remain unnamed was late to market with their technology and made a big deal of the noise characteristics (ground bounce) in FACT. Lots of the marketing people at Fairchild said “don’t acknowledge the competitor’s claims and the issue would go away,” but since I had recently been a system design engineer I was pretty sure the issue wouldn’t go away and our slow sales ramp was proving that true. I began to tear down the competitor’s case one issue at a time. Things

like noise in a lumped load test jig doesn’t simulate noise in a real

The trick to devices getting smaller is more power dissipation in a smaller surface area.

The trick to power efficiency is in complex semiconductor processes and techniques that facilitate faster switching speeds. system with distributed loads and only specific signals in a digital system would be affected by this noise and so on. I created a demo board that showed these factors and travelled around the world with an oscilloscope (and they were pretty big in 1985) and showed small groups of engineers the truth that this was a good technology, if you take the proper precautions.

Again, having just left the design community I knew design engineers don’t believe marketing hype and it was critical to show real waveforms in a live demo environment. This worked and FACT went on to be a

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good revenue generator for many years.

What are you currently working on?

My group is focussing on High Performance Power Discretes (IGBTs, MOSFETs, Rectifiers) and cutting edge Protection devices like ESD and EMI Filters. We have the industry’s first silicon Common Mode Filter. Also, packaging is real important from CSP to high power density packages and IPM’s (Intelligent Power Modules from our Sanyo acquisition).

Can you tell us more about ON Semiconductor and the technology they are developing?

Most of ON Semiconductor is focused on power efficiency: everything from power switching, power control, and power management to low power consumption.

We are working on LED Drivers and ESD protection for LED general lighting.

In the automotive realm we are working on sensors for lane departure and vehicle positioning, extreme high temperature controllers for in transmission & on engine applications and voltage regulation for infotainment & driver information.

In computing and wireless: cutting edge power management for that increases power efficiency and decreases power density.

For example: we are developing

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FEATURED INTERVIEW

engineering functions reporting into me. All of these functions came with a learning challenge but kept life interesting.

INTERVIEW

Other areas include power conversion for high end power supplies and motor control for industrial applications. We are also adopting technology that was developed for hearing aids to provide high quality audio output for cell phones.

On the packaging side we are working on chip scale packaging which reduces the volume of a diode by more than 99% from the most common SMT packages used today.

What direction do you see your business heading in the next few years?

One trend that I am seeing in the industry is that everything is getting smaller and more power efficient.

The trick to devices getting smaller is more power dissipation in a smaller surface area. The trick to power efficiency is in complex semiconductor processes and techniques that facilitate faster switching speeds.

What are some new technologies we can expect to see from ON Semiconductor in the near future?

In the near future, we can expect to see wide band gap technologies, much more use of integrated passive components in filtering, oscillators and RF amplification.

Also, advances in chip singulation will increase the number of die per wafer without changing lithography.

supply chains are getting very complex, and it is getting harder and harder to squeeze the cost out of the products.

What are some of your hobbies outside of work and design?

Having lived in Maine, I must say that my biggest hobby is fishing. I have a vacation home on the coast and I like to go offshore fishing for tuna and sharks. â–

What challenges do you foresee in our industry?

The business cycles are getting shorter and more pronounced,

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FEATURED INTERVIEW

technology for power supplies that will have less than 10mW of power loss in standby mode.

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ADA4096-2/ADA4096-4 F E AT U R E D P R O D U C T S PIN CONNECTION DIAGRAMS ADA4096-2

–INA 2

TOP VIEW (Not to Scale)

+INA 3

8

+V

7

OUTB

6

–INB

09241-001

OUTA 1

5 LDOs, +INB ro PMU with –V 1.2 A4 Buck, Two 300 mA Supervisory, Watchdog, and Manual Reset

The ADA4096-2 dual and ADA4096-4 quad operational amplifiers feature micropower operation and rail-to-rail input and output ranges. The extremely low power requirements and guaranteed operation from 3 V to 30 V make these amplifiers perfectly suited to monitor battery usage and to control battery charging. Their dynamic performance, including 27 nV/√Hz voltage noise density, recommends them for battery-powered audio applications. Capacitive loads to 200 pF are handled without oscillation. For more information, please click here.

Figure 1. 8-Lead, MSOP (RM-8), ADA4096-2 ADP5041

High Performance Micro 20-Lead LFCSP

FUNCTIONAL BLOCK DIAGRAM

OUTA 1

8 +V

VOUT1

The ADP5041 combines one high performance buck regulator and two low dropout regulators (LDO) in a small 20-lead LFCSP to meet 7 OUTB –INA 2 demanding performance and board space requirements. The high TOP VIEW switching frequency of the buck regulator enables use of tiny multilayer +INA 3 (Not to Scale) 6 –INB external components and minimizes board space. When the MODE pin is set to logic high, the buck regulator operates in forced PWM mode.

5 +INB –V 4 When the MODE pin is set to logic low, the buck regulator operates in PWM mode when the load is around the nominal value. When the load current falls below a predefined threshold, the regulator operates NOTES in power save mode (PSM), improving the light load efficiency. For more 1. CONNECT THE EXPOSED Figure 1.

LTC2996 PAD TO GROUND. information, please click here.

RFILT = 30Ω

AVIN

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09652-001

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Figure 2. 8-Lead LFCSP (CP-8-10), ADA4096-2High Accuracy Temperature Monitor 6

VCC

8

VREF

+

1.8V

1.2V

–

200k

The LTC2996 from Linear Technology Corporation measures a remote diode’s temperature with ±1°C accuracy and its own die temperature with ±2°C accuracy while rejecting errors due to noise and series resistance.

The device provides a voltage-proportional-to-absolute-temperature output, as well as individual undertemperature and overtemperature alert outputs, defined by user-adjustable thresholds. No code is required to configure the device. With a 200µA quiescent current, the LTC2996 simply provides a precise, space-saving, micropower temperature monitoring solution. For more information, please click here.

or ADA4096-4, see the Pin Configurations and Function tions section.

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range of the ADP5041 LDOs extend the battery life of portable T TO V V devices.

The1ADP5041 LDOs maintain a power supply rejection CONVERTER 5 greater than 60 dB for frequencies as high as 10 kHz while D GND D voltage. operating with a low headroom 7 4 3

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2996 BD

Each regulator in the ADP5041 is activated by a high level on the respective enable pin. The output voltages of the regulators and the reset threshold are programmed through external resistor dividers to address a variety of applications. The ADP5041 contains supervisory circuits that monitor power supply voltage levels and code execution integrity in microprocessor-based systems. They also provide power-on reset signals. An on-chip watchdog timer can reset the microprocessor if it fails to strobe within a preset timeout period.

T

EMI Test Receiver for Reduction of Test Times Rohde & Schwarz introduces the new R&S ESR EMI test receiver whose broadband architecture allows standard-compliant EMI measurements up to 6000 times faster than other solutions. Comprehensive diagnostic tools such as spectrogram display, realtime spectrum analysis and IF analysis help developers detect and eliminate EMI. The R&S ESR test receiver is available in two different models for frequencies ranging from 10 Hz to 3 GHz or 7 GHz to meet the requirements of all users 7 who perform EMC certification on commercial equipment. For more information, please click here.

2996f

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. www.analog.com Tel: 781.329.4700 Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved.

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FEATURED PRODUCTS

30V, Micropower, Over-voltage Protection

C eb om .c m om un ity

W eb Ele ct ric al En w gi w ne w er .e in ew g

EE Making Wireless Truly Wireless: Need For Universal Wireless Power Solution

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ARTICLES

dicta sunt explicabo. Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit, sed quia non numquam eius modi tempora incidunt ut labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil

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TECHNICAL ARTICLE TECHNICAL ARTICLE

Authors: Alexei Zernov Yngve Wernqvist & Chris Young Intersil

Digital Power Solutions Offer Performance and Integration Enhancement Introduction Digital power is a technical term used to name a way of controlling power conversion by using digital signal processing techniques. We are in the middle of a revolution where the advantages of digital power are being applied to power conversion and real advancements are being made in the areas of efficiency, power density, reliability, robustness and ease of use.

Although the first digital control

ideas are more than 30 years old, we are just now being to see the widespread use of this technology.

a digital signal. Thus, it was a natural concept to consider a digital controller for generating the PWM.

Digital Power Architecture Evolution

Some of the earliest digital power controllers used special purpose microprocessors called digital signal processors (DSP) and general purpose microcontrollers (uC). In these controllers, the analog signal representing the output voltage of a regulated power supply was digitized and the digital signal was then processed in the

The process of regulation and control of a switching power supply includes generation of a pulse width modulated (PWM) signal which drives one or more power transistors. The PWM signal is, in all switching regulators, in a sense

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Power Management

SCL

Digital PWM Controller

Controller Interface Digital VREF +

ADC

L

–

∑

M

DSP

compared to analog world controllers. All of this enables digital power technologies to deliver new levels of conversion performance, functionality and integration.

N

VOUT

Driver

DPWM

Improved Efficiency Thanks to digital control, the Zl6105 is capable of executing algorithms to optimize the dead-time applied between the gate driver signals for the top and bottom FETs. In a synchronous buck converter the MOSFET drive circuitry must be designed such that top and bottom MOSFETs are never in conducting state at the same time. Conversely, a long period of time which both MOSFTS are off reduces circuit efficiency by allowing current to flow in their parasitic body diodes.

The ZL6105 has an algorithm that constantly adjusts dead-time nonoverlap to minimize losses, thus maximizing efficiency. This circuit will null out dead-time differences due to components variation, temperature and loading effects.

Figure 1: Digital Power Controller Using DSP or General Purpose Microcontroller

Advantages of Digital Power Architecture Digital signal processing technology is ideally suited for digital PWM signal generation and allows implementation of advanced processing algorithms: filters, performance optimization algorithms, and nonlinear control and auto-compensation. Optimized, low power voltage setting DAC and Voltage and Current monitoring ADC’s provide telemetry facilities and information far advanced Input Voltage Bus PG

EN

MGN

CFG(0,1,2) ILIM SS

V(0,1)

FC(0,1)

VDD VR

Power Management

VTRK

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NVM

PID Digital Compensator

BST MOSFET Drivers

D-PWM

SW

VOUT

NLR SYNC

PLL

–

About 10 years ago, dedicated function state machine based digital power controllers began to appear, first in academia and then in commercial offerings. These state machines were designed specifically to be used as digital switching power supply controllers.

Controllers contained specialized HW peripherals for power conversions purposes. They were optimized to the point that digital power started to be economically viable across a wide range of applications. This was that turning point in the history of digital power.

A block diagram of the modern digital power converter ZL6105 is shown in Fig 2. A regulation

loop key element is a special state machine - PID Digital Compensator.

ADC

∑

VSEN ISENB

+

DSP. While the DSPs were quite capable in terms of processing power, to achieve the fast processing speeds needed for high frequency switching power supply control, high clock speeds were required.

The high clock speed and the inherent high bias current required in those DSPs meant a significant amount of power was consumed in the power conversion process.

Furthermore, the DSPs were too expensive for the switching power supply applications. See Fig 1.

REFCN

DAC

ADC

ISENA VDD

DDC I2C

SALRT SDA SDL SA(0,1)

Communication

ADC

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Voltage Sensor

VSEN+ VSEN – XTEMP

Temp Sensor

Figure 2: Digital Power Controller ZL6105 Using PID Digital Compensator and Optimized Set of HW Peripherals

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TECHNICAL ARTICLE

SDA

TECHNICAL ARTICLE

TECHNICAL ARTICLE CIN

DDC

ZL9117M COUT

Ease of Use and AutoCompensation

CIN DDC

ZL9117M

VOUT COUT

Figure 3: Two ZL9117 Modules Using Communication via DDC Bus for Current Sharing

Integration and Reliability Reliability is a term used to describe the relative likelihood that a power supply will not fail. In general, the reliability of any system, including a power supply, decreases with an increase in the number of components.

An advantage of modern digital power controllers is that they are highly integrated and require fewer components to achieve a full featured power supply.

The ZL6105 digital power controller integrates not only the power conversion control but power management, fault management, and telemetry. Synchronization functions such as ramp up and down sequencing, switching phase spreading, current sharing, fault spreading and others are performed using communication via a proprietary communication bus. The system monitoring from the host is performed via I2C interface using the industry standard Power Management Bus commands (PMBus™). All this

eliminates dozens of components from the design.

Further HW integration, and therefore reliability improvement can be found in integrated FET controllers like the ZL2101 and even fully integrated power supply modules like the ZL9117. Fig 3 shows how easily two ZL9117 modules can be combined to build a two phase current sharing rail.

Stability is a critical operational requirement for power supplies. In regulated power supplies, stability is controlled by the characteristics of the feedback path. Power supply engineers need to ensure stable operation over all load conditions, environmental conditions and component characteristic variations.

Design of the feedback loop to be stable under all of these conditions is a time consuming task.

Digital power robustness is enhanced by ability to monitor and respond, in an optimal way,

Digital power solutions provide an alternative to analog compensation.

Digital compensation has no external components and can be tuned just by changing the gain values stored in digital registers.

Digital filters are not simply replacements of analog filters.

Digital filters can perform functions

to environmental changes. As an example, the ZL6105 monitors both the internal die temperature and external temperatures.

This allows the controller to compensate temperature sensitive measurements for accurate

that go far beyond the capabilities of analog filters. For example, in high Q (>0.5) second order circuits, the poles in the plant are complex conjugate poles which may require complex conjugate zeros in the compensation network to effectively

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TECHNICAL ARTICLE

control and monitoring.

Input, output voltage and output current monitoring allows ZL6105 to detect system faults and prevent of catastrophic consequences for power supply and load by configurable fault reaction.

VIN

3.3V to 5V

TECHNICAL ARTICLE

Figure 4: Transient Respond of the Power Supply System Before (Upper Graph) and After Auto Compensation (Lower Graph)

compensate. Conventional analog compensators only provide real zeros for compensation. On the other hand, digital filters can easily provide the complex conjugate zeros to compensate high Q power supplies.

Nonetheless, even this advantage, in many cases is not enough to stabilize and optimize a power supply over all conditions. Initial inductor and capacitor values can vary by +/- 10% . This can significantly change the control loop even to the extent that the power supply has substantially degraded stability. For example, electrolytic capacitor characteristics such as the capacitance and ESR can greatly change with temperature.

What is really needed is a method for compensating power supplies that is automatic.

Intersil’s Zilker Labs has recently released several parts with auto compensation. All of those use an advanced digital algorithm to characterize the plant and to determine appropriate compensation settings for stable operation.

During auto-compensation, the microcontroller adjusts the state machine to stabilize the power conversion process by adjusting the compensation coefficients in a systematic way while observing the response of the system. While this does produce a slight perturbation on the output it is almost imperceptible and well within the allowed transient envelop.

In practice, auto compensation is easy to use. Simply enable the power supply and the controller does all of the work. Fig4 shows the transient response of a typical power supply before (upper) the supply is adequately compensated.

The second trace (lower) shows the transient response after auto compensation.

An additional benefit of automatic compensation is that the plant is characterized by the compensation algorithm. The values of Gain, Q, and Natural Frequency can be monitored over the life of the power supply and significant changes in the plant can be observed, many times, before failure of the system.

This allows the user to incorporate predictive diagnostics of the system health for improved reliability.

Auto-compensation saves the design engineer a considerable

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amount of time, producing a more stable power supply and potentially improves the reliability and robustness of the power supply system.

Conclusion Digital power control offers many advantages over traditional analog controllers in terms of optimal performance, reliability, high number of features, and ease of use.

Switching from traditional analog power control to digital power control is easy and rewarding.

About the Authors Chris Young serves as Sr. Manager for Digital Power Technology at Intersil Zilker Labs. Previously he served Chief Technical Officer for Zilker Labs.

He has over 20 years of experience in the management of research and development of state of the art electronic systems. He was one of the founders and vice president of technology at ColdWatt, Inc. Prior to that, he held technical and engineering management positions at leading companies including Dell, Astec Power, Lucent/Bell Labs and Unison Industries. He has had numerous publications and patents in the areas of pulsed power, power control and conversion, and stability analysis. Mr. Young holds Bachelor’s degree in Physics from the University of Texas and a Master’s degree in Electrical Engineering from Texas Tech University where he also serves on the Industrial Advisory Board. ■

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All these converters use a dedicated state machine for the digital PWM controller and an embedded microcontroller to monitor the circuit, environmental conditions, and configuration profile to setup and modify the state machine operation in real time.

Get the Datasheet and Order Samples http://www.intersil.com

1.8V to 3.3V, Micro-Power, ±15kV ESD, +125°C, Slew Rate Limited, RS-485/RS-422 Transceivers ISL32600E, ISL32601E, ISL32602E, ISL32603E The Intersil ISL32600E, ISL32601E, ISL32602E and Features ISL32603E are ±15kV IEC61000 ESD protected, micro power, wide supply range transceivers for differential communication.

The ISL32600E and ISL32601E operate with VCC ≥ 2.7V and have maximum supply currents as low as 100µA with both the transmitter (Tx) and receiver (Rx) enabled. The ISL32602E and ISL32603E operate with supply voltages as low as 1.8V. These transceivers have very low bus currents, so they present less than a “1/8 unit load” to the bus. This allows more than 256 transmitters on the network, without violating the RS-485 specification’s 32 unit load maximum.

• Single 1.8V, 3V, or 3.3V Supply

Rx inputs feature symmetrical switching thresholds, and up to 65mV of hysteresis, to improve noise immunity and to reduce duty cycle distortion in the presence of slow moving input signals. The Rx input common mode range is the full -7V to +12V RS-485 range for supply voltages ≥ 3V.

• Up to 65mV Hysteresis for Improved Noise Immunity

Hot Plug circuitry ensures that the Tx and Rx outputs remain in a high impedance state while the power supply stabilizes.

• -7V to +12V Common Mode Input/Output Voltage Range (VCC ≥ 3V)

This transceiver family utilizes slew rate limited drivers, which reduce EMI, and minimize reflections from improperly terminated transmission lines, or unterminated stubs in multidrop and multipoint applications.

• Half and Full Duplex Pinouts; Three State Rx and Tx Outputs

The ISL32600E and ISL32602E are configured for full duplex (separate Rx input and Tx output pins) applications. The half duplex versions multiplex the Rx inputs and Tx outputs to allow transceivers with output disable functions in 8 Ld packages.

Applications

• Low Supply Currents . . . . . . . ISL32601E, 100µA (Max) @ 3V . . . . . . ISL32603E, 150µA (Max) @ 1.8V - Ultra Low Shutdown Supply Current . . . . . . . . . . . . . . 10nA • IEC61000 ESD Protection on RS-485 I/O Pins . . . . . . ±15kV - Class 3 ESD Levels on all Other Pins . . . . . . . . . >8kV HBM • Symmetrical Switching Thresholds for Less Duty Cycle Distortion • Data Rates from 128kbps to 460kbps • Specified for +125°C Operation • 1/8 Unit Load Allows up to 256 Devices on the Bus

• 5V Tolerant Logic Inputs • Tiny MSOP Packages Consume 50% Less Board Space

• Differential Sensor Interfaces • Process Control Networks • Security Camera Networks • Building Environmental Control/Lighting Systems

10m

ISL3172E DYNAMIC (9.6kbps) 1m

25°C, RD = ∞, CD = 50pF

100µ

ICC (A)

ICC (A)

ISL3172E STATIC

ISL3260XE DYNAMIC (9.6kbps)

DYNAMIC (256kbps)

DE = VCC, RE = GND

DYNAMIC (128kbps) 1m

ISL3260XE STATIC STATIC DE = VCC, RE = GND

10µ 2.7

2.8

2.9

3

25°C, RD = ∞, CD = 50pF 3.1

3.2

3.3

3.4

3.5

SUPPLY VOLTAGE (V)

FIGURE 1. ISL32600E AND ISL32601E HAVE A 9.6kbps OPERATING ICC LOWER THAN THE STATIC ICC OF MANY EXISTING 3V TRANSCEIVERS

June 22, 2012 FN7967.0

3.6

100µ 1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

SUPPLY VOLTAGE (V)

FIGURE 2. ISL32602E AND ISL32603E WITH VCC = 1.8V REDUCE OPERATING ICC BY A FACTOR OF 25 TO 40, COMPARED WITH ICC AT VCC = 3.3V

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2012 All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

Using Analog Components

to Manage Power in Low-Power Solar Systems Martin Tomasz

Touchstone Semiconductor - Senior Scientist

From large panels to harvested microwatts from a few

photodiodes, solar power is increasingly prevalent in autonomously powered systems. With the worldwide evolution toward lower power operation using more “green� energy sources, emphasis on deploying solar power in a greater variety of environments has been on the rise.

In low-power solar systems, it is critical to assess whether there is sufficient sunlight at a given time to power the system. In some cases, this involves determining whether there is sufficient power to enable the microcontroller. In many ultra-low-power systems, the simple act of waking the microcontroller to make a voltage measurement might collapse the solar source or waste precious power from a reservoir capacitor.

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TECHNICAL ARTICLE 1V2.5V C2 0.1µF

+

Power Status

R2 2.2M

good wait

U1 TS1001

–

D1 photodiode

TECHNICAL ARTICLE

T1 2N3906

Measured Light

R1 100k

(adjust for photodiode)

V lux

C1 0.01µF Figure 1: An ultra-low power op amp can be a continuous, “always-on” measurement mode.

One solution is to incorporate a simple analog op amp into the system. An ultra-low-power analog op amp can support “always-on” circuitry around the microcontroller and may be the simplest and best solution.

Ultra-Low-Power Op Amps Figures 1 to 3 illustrate a few simple circuits using an ultra-low-power op amp in a continuous “always-on” measurement mode assessing the state of the solar cell.

The technique hangs on using an op amp whose total power is as low as practical driven primarily by ultra-low supply voltage operation.

1.8V2.5V

+ D1 photodiode

R1 100k

–

(adjust for photodiode)

The circuit in Fig. 1 shows a photodiode in photovoltaic zero-bias mode. The short-circuit current is measured and converted to a voltage across resistor R1 while the feedback action of the op amp forces 0 V across D1.

Zero-bias photovoltaic current is a convenient parameter that is generally well characterized and can be directly referenced to most photodiode manufacturer datasheets.

Note that with the rail-to-rail input range of the analog op amp, in this case Touchstone Semiconductor’s TS1001 op amp, the photodiode may be connected directly to the positive supply voltage rail.

The circuit in Fig. 2 generates a simple positive-polarity output for a similar zero-bias-mode measurement. In

C2 0.1µF

U1 TS1001

Measured Light V

C1 0.01µF

lux

Figure 2: An ultra-low-power op amp offers simple, positive polarity output to support a zero bias condition.

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TECHNICAL ARTICLE

Power Source

Load

(solar cell)

(uC, etc)

R10 5.1M C1 47µF

R7 365K 1%

R1 test load

U2 TS1001

+

R8 1.4M 1% R2 220K T1 BSH105 N-ch

R5 5.1M

R6 510K

+ –

U1 TS1001

R3 1M

C2 10nF

R9 220K

–

Power Status wait

R11 220K

T3 BSH105 N-ch

R5 510K

good

T4 BSH105 N-ch

Power Check

T5 BSH105 N-ch

disable enable

Figure 3: An ultra-low-power op amp-based circuit assesses a PV solar-cell source.

this case, the op amp servos its output to sink sufficient current to support the zero bias condition for D1. This creates a voltage across resistor R1 at the negative supply voltage pin of the TS1001. Since this ultra-lowpower op amp contributes less than 1 μA to this current, the current measured from D1 has minimal error.

temporarily holds the voltage to keep this circuitry and any standby loads powered. Op amp U2 serves as a comparator, tripping when the power source drops more than 25% (with 5% hysteresis). Transistor T3 latches the result, while transistor T4 resets the latch during each assessment period to ensure a fresh reading.

For a more comprehensive assessment, the circuit in Fig. 3 tests the solar source to see if it can handle the load. The circuit shown makes this assessment without burdening the microcontroller and risking collapse of the supply during measurement.

Such test loading is useful for determining the available power from a solar cell, since merely measuring the open circuit voltage generally does not provide an accurate assessment.

Approximately once per 100 ms, the circuit disconnects the solar-cell power source from its reservoir capacitor and load, applying a test load (R1) and assessing the resulting voltage drop. If the voltage drops 25% or more, the result is latched into U2 and the power status is provided to the microcontroller.

This ultra-low power circuit draws less than 3 μA at 1V. Op amp U1 provides the timer function and controls transistor switches T1 and T2 to apply the test load while simultaneously disconnecting the load. Capacitor C1

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Assessing “Always-On” Circuitry Generally, an ultra-low-power op amp, like Touchstone Semiconductor’s TS1001, is an excellent option for supporting “always-on” analog circuitry. For example, op amps that are guaranteed to operate under 1 V and consume less than 1 μA current may be configured as a filter and left continually on, so that a microcontroller making an ADC measurement does not have to stay powered on while the filter settles.

In conclusion, ultra-low-power op amps are useful in

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TECHNICAL ARTICLE

T1 BSH205 P-ch

TECHNICAL ARTICLE TECHNICAL ARTICLE

low-power solar systems to assess the available power from solar cells before a load is applied, and generally to support standby, “always-on” circuitry, while drawing negligible currents.

About the Author Martin Tomasz is principal of Touchstone Semiconductor, an engineering consulting company offering expertise in circuit and systems design. Mr. Tomasz is a seasoned analog and mixed signal engineer with 22 years experience in circuit and systems design. Past experience includes 12 years at Maxim Integrated Circuits where he was Senior Scientist, and Quantance, where he was VP Product Architecture. He currently holds 12 patents. ■

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