Lighting Electronics: July 2014 by EEWeb Magazines

July 2014

Interview with Dr. Karsten Diekmann, Senior Manager Marketing, Product & Application Engineering OSRAM OLED

INNOVATIVE

LIGHTING from OSRAM Shines Down the Road

Testing that Tells the Truth Shift Registers Reduce Size and Cost in Designs

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determined by the PCBA circuit design will create different forward current and voltage relationships, which will result in different LED readings, as shown in figure 3.

Lighting Electronics

CONTENTS

ENVIRONMENT AND TEST METHODOLOGY Open air, semiventilated, or enclosed environments will cause totally different results for LED wavelength and luminosity readings. A wafer-testing environment is vastly different from an in-circuit test environment. In the PCBA contract manufacturing environment, the LED light sensor is mounted inside the fixture, light from the LED is collected through a light pipe, and the light is directed to the LED sensor, as shown in figure 4.

based ementation

ntrollers have dedicated ks to drive PWM. For ess’ PSoC4 has a CPWM that implements ed PWM drive. Generally, using a timer with a ability, and the logic is mware logic discussed er will have a compare with the period register. ster is loaded with a the pulse width and egister is loaded with al to the ON time. The an output that goes the compare value is he tick value and goes Also the tick value rolls back to zero when it aximum value (65535 for This output is routed to driving the LED directly are block.

Figure 3. Forward voltage versus forward current.

Firmware based vs. Hardware based PWM Implementation

“In an actual electronicsmanufacturing Requires an advanced controller with hardware environment, PWM block application of theory Typically, only a few PWM blocks are required to fully realize can pose serious a multi-channel PWM challenges.” Restricted pin assignment as the

Firmware based Implementation

Hardware based Implementation

TECH ARTICLE

Low-cost controller with one timer is sufficient One timer is enough to implement a multi-channel PWM Free pin assignment

Testing That Tells the Truth Expectations for PCBA-Level LED Tests

hardware blocks usually support fixed pins for PWM drive

Need to serve frequent interrupts, causing CPU overhead. Also, frequency of the interrupts increases with the increase in required brightness levels and number of PWMs controlled

Figure 4. No interrupts, CPU is 100% available for other code LED light pipe and LED sensors

Strict interrupt latency control is required to avoid jitter

Not to worry about interrupt latency

Limitation on the maximum achievable resolution

No limitation (depends on the width of the period and compare register of the timer)

Less accurate PWM control

More accurate PWM control

Not possible to put CPU into sleep during PWM drive, thus drawing more power

Ability to put CPU into sleep, thus drawing less power

in an ICT test fixture.

TECH ARTICLE

Lighting the Future

Philips Lumileds envisions a future that places the consumer at the helm. Bright Future for Philips Lumileds examined different ways g PWM. In Part 3, we’ll The Philips hue system combines LED Next-Gen LEDs on challenges faced g systems with capacitive lighting, wireless communication, and D lighting, and how to Table 1. m. smart devices to enable users to tune LUXEON 3030 2D both color and luminosity from anywhere LUXEON 3535 2D in the world using a phone, tablet, or The LUXEON 3535 2D and LUXEON 3030 computer. “I think hue is a prime example 2D midpower LEDs recently introduced by Combining Capacitive of Sensing the Philips vision around connected ed for specifi Ds are t. LEDs Philips Lumileds put two die next to each the LE en rr ard cu rw and LED Lighting fo lighting,” commented Lesaicherre. “The and an 6V or gher th will tages hi other inside a single package. Not only s 70mA exceed at th t idea,” he noted, “is to allow users to en . al driver extern does this innovation lower component control their environments as they please register PUTS e shift count in retrofit lamp design, the two s to th es ut at tp in n ou through an easy-to-use and appealing at elim tion th n yield hip solu . This ca die architecture produces double the l driver erials, at xterna m of product. We see applications of that in e the bill can driv tions in register e shift light, which is essential in maximizing the ut of th homes where people want to change the ly. r shift atic foInnovative Lighting from OSRAM e such t schem a dollar number of lumens can buy. s. ic for on hemat output 3. Outpu P, sc in re X ra ut N gu -d tp atmosphere in the evening to warmer or Fi en from the ou with op driver r 6A LED register s simila nction Shines Down the Road PIC6C59 ster fu ift-regi ) metal V sh brighter colors.” In their studies on the (H s ne oltage stor a high-v t transi 5 with d-effec el fi r to effects of lighting on users, Philips found conduc “The Philips hue system driver. e in plac ed us that exposure to bluish lights enhances 6C596A t e NPIC acemen hows th this repl creating Making drivers, al rn HC595. er combines LED lighting, r exte the ability to concentrate or to study. s a low need fo and ha es the mpact more co that is The research also showed that exposure ls. at materia tputs th wireless communication, rain ou ed open-d gn ve si ha de s to warmer is Shift Registers Reduce Size light in the evening—reddish output C device ound . Each it on gr to 33V is no lim 0mA lerant sink 10 d there ly an 5. ve A ti 59 m C light n ac t74H k 100 and smart devices toLED Designs like the sunset—allows people to tputs ca placing Cost in e curren re 6Aand the ou s includ nt. All PIC6C59 aximum output N . m 4 he A T re m 0 Figu ously. ts a 25 sleep better at night. ultane ut also hich se ch outp uitry, w

rizes the differences are-based and ed PWM implementations.

TECH ARTICLE

With its luminaire, called ‘Rollercoaster’ for its interesting architectural design, OSRAM demonstrates the industry maturity of transparent OLED.

COVER INTERVIEW

TECH ARTICLE

Interview with Dr. Karsten Diekmann, Senior Manager Marketing, Product & Application Engineering OSRAM OLED

enable users to tune both color and luminosity from anywhere.”

d ea ting circ rrent, an g these able cu . Havin n the sink vice ca otection mal pr 596A de er 6C th IC s the P lude the N s than D ns LE ea sm e of higher er rang otection e a wid erate at to driv s that op t. e used ing LED curren d ud cl ar in rw 5, gher fo 4HC59 with hi es and voltag

As night falls on incandescent bulbs, innovations in lighting promise to enhance the quality of life. So, with the arrival of Philips Lumileds LEDs at a reasonable price, it’s time to embrace next-generation lighting and say, “Hello,” to a new and brighter world.

Lighting Electronics

TESTING That Tells the Truth Expectations for PCBA-Level LED Tests

n in-circuit test system (ICT) measures a componentâ&#x20AC;&#x2122;s values on the printed circuit board. For instance, the ICT can check if the measured value of a resistor is within its nominal range as specified on the datasheet. The same theory applies for testing LEDs with ICTâ&#x20AC;&#x201D;the tester should be able to test to see if the luminosity and wavelength values are within the ranges indicated on the LED datasheet.

By Yang Hua and Shi Zhi Min, Agilent Technologies On August 1, 2014, Agilent Technologies, Inc. Electronic Measurement Group will become Keysight Technologies, Inc.

TECH ARTICLE

Lighting Electronics

ndividual LED specifications are measured under very controlled environments. In an actual electronicsmanufacturing environment, application of theory can pose some serious challenges to the contract manufacturer whose shop-floor test station is affected by various environmental factors, including space, equipment, and even lighting constraints. It is important to have reasonable expectations about testing an LED on printed circuit board assembly (PCBA) in the contract-manufacturing environment. Letâ&#x20AC;&#x2122;s have a brief look at the factors that affect LED test results.

TEMPERATURE

Figure 1. Ambient temperature versus forward current.

In a typical LED datasheet, the specifications will state the LED characteristics at a specified current and with a die temperature of say, 25Â°C. Temperature affects the behavior of an LED; an increase in the junction temperature of an LED will affect the light output and forward voltage of the LED at a specific current. It will show a very different luminosity rating during testing at different temperatures. As the LED heats up, the ambient temperature starts affecting the forward current (figure 1), resulting in different luminosity values (figure 2). Hence, these values should be taken as reference only and not for actual test readings.

Figure 2. Forward current versus relative luminosity.

TECH ARTICLE DRIVING VOLTAGE In reality, different applications as determined by the PCBA circuit design will create different forward current and voltage relationships, which will result in different LED readings, as shown in figure 3.

Figure 3. Forward voltage versus forward current.

â&#x20AC;&#x153;In an actual electronicsmanufacturing environment, application of theory can pose serious challenges.â&#x20AC;?

Figure 4. LED light pipe and LED sensors in an ICT test fixture.

Lighting Electronics

BEST TEST The practical way of testing LEDs with an ICT is through a planned learning process, which measures the LED values from a known good board. Within the same test environment and methods, LED values on the PCBAs are then measured and evaluated against data from the known good board during manufacturing. In-circuit testing of LEDs can provide contract manufacturers with substantial benefits: • Compared with other LED test solutions, some ICT-based LED test solutions like the Agilent LED Test provide a parallel measurement technique, which allows simultaneous measurement of up to 128 LEDS per single measurement card. The software will generate a parallel test to light up the LEDs while measuring them at the same time.

“Open air, semiventilated, or enclosed environments will cause totally different results for LED wavelength and luminosity readings.“

Figure 5. Color waveform sampling.

• The Agilent LED test provides an innovative color waveform-analyzer feature, as shown in figure 5. It samples LED light wavelengths and luminosity on a real-time basis. Some power-indicator LEDs or status LEDs automatically turn on during powered testing or boundaryscan tests. This LED data will be automatically captured by the color waveform analyzer without requiring any additional test resources and will increase the coverage by measuring the LED wavelength and intensity. Looking ahead, new LED test technologies such as ICT LED tests can be widely used and integrated onto other platforms like functional test stations or customized test solutions to increase test coverage even with limited test resources.

REFERENCES Color Logical Analysis Approach for LED Testing in Manufacturing Avago LED Datasheet

TECH ARTICLE

â&#x20AC;&#x153;ICT-based LED test solutions like the Agilent LED Test provide a parallel measurement technique, which allows simultaneous measurement of up to 128 LEDS per single measurement card.â&#x20AC;?

ABOUT THE AUTHORS

Yang Hua is a Product Marketing Engineer with extensive experience in the manufacturing and electronics measurement industry. She has seven years of marketing and field experience and strong knowledge of current and advanced in-circuit test technologies. Zhi Min Shi is a Principal R&D Software Engineer and lead software architect in developing test solutions for the manufacturing industry. For the last 10 years, his major projects coverage includes in-circuit test, boundary scan test, functional test, LED test, IC reliability test, and test executive. His enthusiasm is driven with the goal of achieving the most cost-effective test solutions for the end user. Prior to his career in the manufacturing test domain, Zhi Min was involved with the development of tiny smart cards (widely used in 3G network systems), popular elevator control systems, and missioncritical railway signal systems.

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Protecting Protecti ing Technology. Protecting Life.

Lighting Electronics

Bright Future for

Philips Lumileds

NEXT-GEN LEDS By Heidi Pluska Contributing Writer

TECH ARTICLE

ay good-bye to incandescent light bulbs, and get acquainted with the next generation of lighting. With government regulations banishing old

familiar bulbs, compact fluorescent lights (CFL) and light-emitting diodes (LED) are the replacements of the day. CFL bulbsâ&#x20AC;&#x201D;clunky, mercury-ridden, hard to dim, and excessively whiteâ&#x20AC;&#x201D;are unpopular. And LED bulbs, while a good alternative in terms of energy consumption, color, and environmental impact, are expensive. The success of Philips Lumileds LEDs, however, offers hope for future lighting. By raising quality and dropping price, their next generation of LEDs are poised to retire CFLs and usher in a new dawn for lighting.

Lighting Electronics

Blue + Yellow = White At the heart of a packaged LED device is a LED chip that directly converts incoming electrons (electricity) into photons or visible light. But unlike incandescent bulbs or CFLs, LEDs are nearly monochromatic. That is, the color they emit is limited to a specific wavelength. Because white light is a combination of all the wavelengths of the visible spectrum, there is no such thing as a white LED. To produce a “white” LED, manufacturers start with a blue LED chip, also referred to as a blue “pump” over which a yellow-based phosphor is applied. This combination of colors makes use of a phenomenon known as metamerism which occurs when the eye and brain perceive two different but complementary colors mixing to create a third color. When the blue light shines through the yellow phosphor, it’s downconverted into what we see as white light.

Color-Rich and Affordable LEDs Engineering an LED that matches the appealing hue of an incandescent bulb is an art Lumileds has mastered. And their involvement in every step of the development process has enabled Lumileds to maximize efficiency and minimize costs. In an interview, Pierre-Yves Lesaicherre, CEO of Philips Lumileds, explained to EEWeb, “We develop the epitaxy of the blue LED, which is the basis of every white LED.” Lesaicherre added, “for the epitaxy, we do the research and development

“We are one of the few LED companies that does research and development on phosphors.” ourselves. We also produce the phosphor materials—we are one of the few LED companies that does research and development on phosphors. Finally, we develop all of the semiconductor processes that go on top of the LED as well as the packaging. We are involved in every step of the fabrication of our LEDs.” In addition to streamlining the development process, Lumileds has also managed to drop the cost-per-unit of their LEDs further by amplifying the scale of their manufacturing operation. As Lesaicherre noted, “We are trying to increase the yield year after year, and we have achieved significant progress in the last two years. Our yields have gone from the mid-70 percent range to the 90 percent range, which is about the same range as semiconductors. This means that our LED devices will be much cheaper to produce, and they’ll be more efficient.”

TECH ARTICLE

Demand for Midpower LEDs Philips Lumileds high-power LED products are the most visible on the market, but midpower LED productgrowth rates are expected to exceed those of high-power products since midpower LEDs can greatly reduce the cost of LED chips manufacturers use in lamp designs. For example, a 50W PAR20 lamp can be achieved using only four LEDs, while a 40W A19 lamp that previously required 14 LEDs can now be created using only six. “Initially, high power was the only solution in

illumination, and midpower was really confined to TVs and monitors,” said Lesaicherre. “Progressively, we’ve seen the entry of midpower LEDs into illumination products, which is why,” remarked Lesaicherre, “we decided to complement our high-power offering with our midpower products. In distributed lighting applications, these devices are more efficient with a better lumens-per-dollar offering, which makes them more desirable for mass-market adoption.”

Lighting Electronics

Lighting the Future

LUXEON 3535 2D

LUXEON 3030 2D

The LUXEON 3535 2D and LUXEON 3030 2D midpower LEDs recently introduced by Philips Lumileds put two die next to each other inside a single package. Not only does this innovation lower component count in retrofit lamp design, the two die architecture produces double the light, which is essential in maximizing the number of lumens a dollar can buy.

“The Philips hue system combines LED lighting, wireless communication, and smart devices to enable users to tune both color and luminosity from anywhere.”

Philips Lumileds envisions a future that places the consumer at the helm. The Philips hue system combines LED lighting, wireless communication, and smart devices to enable users to tune both color and luminosity from anywhere in the world using a phone, tablet, or computer. “I think hue is a prime example of the Philips vision around connected lighting,” commented Lesaicherre. “The idea,” he noted, “is to allow users to control their environments as they please through an easy-to-use and appealing product. We see applications of that in homes where people want to change the atmosphere in the evening to warmer or brighter colors.” In their studies on the effects of lighting on users, Philips found that exposure to bluish lights enhances the ability to concentrate or to study. The research also showed that exposure to warmer light in the evening—reddish light like the sunset—allows people to sleep better at night. As night falls on incandescent bulbs, innovations in lighting promise to enhance the quality of life. So, with the arrival of Philips Lumileds LEDs at a reasonable price, it’s time to embrace next-generation lighting and say, “Hello,” to a new and brighter world.

TECH ARTICLE

“The hue bulbs are based upon Philips Lumileds LUXEON Rebel ES series, which includes the industry leading lime LED.”

Lush GREENS The hue starter kit includes a wireless router and three RF-enabled bulbs, each with an individual IP address. According to Lesaicherre, assigning each lamp a unique IP address enables hue users the ability to create up to 16 million different colors. Hue utilizes the Zigbee wireless protocol, which allows for very low-power communication between each lamp and the hub. The hue bulbs are based on Philips Lumileds LUXEON Rebel ES series, which includes the industry leading lime LED. “Inside of the hue lamp, we installed three types of LEDs: blue, red, and green LEDs. The key to unlocking 16 million colors with high efficacy,” explains Lesaicherre, “lies with

LUXEON Rebel ES Lime

LUXEON Z Lime

the green LED, which is what we refer to as ‘lime green.’” He further notes, “In the LED industry, blue and red LEDs are very well mastered; however, the green LED is not as easy to produce. The epitaxy that emits a direct green color is very low efficiency, which means you need many LEDs to do green, up to twice as many as red. For hue, we did two years of research and development on phosphors. We took a blue LED and completely turned the blue photons into green photons at a high efficiency.” This is absolutely unique to Philips Lumileds—no one else in the industry is capable of producing this saturated green color at such high efficiency.

Lighting Electronics

Combining

CAPACITIVE SENSING and LED LIGHTING (Part 2)

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

TECH ARTICLE

Pulse Width Modulation (PWM)

n part 1, we explored different LED lighting techniques adopted in capacitive sensing-based UI applications using real-world use cases. Next we’ll learn the different approaches for implementing pulse width modulation (PWM), a key method for LED control applications.

PWM has mainly two properties: Frequency:

Using a PWM signal rapidly switches an LED on and off. As the switching frequency produces LED flickering, the PWM frequency should be >100 Hz to ensure that a human eye doesn’t perceive this effect.

Duty cycle:

PWM controls the brightness of LEDs by changing the duty cycle and keeping the load current constant. The average current seen by the LED depends on the duty cycle. Average current increases as duty cycle increases, in turn increasing the brightness. The duty cycle needs to have as many steps between 0% and 100% as the number of brightness levels required in an application. For example, an application requiring 20 brightness levels from fully off (0%) to fully on (100%) should be able to control the duty cycle in the steps of 5% (total 20 steps, excluding fully off).

There are two ways to implement PWM with a microcontroller. Either implement the entire PWM logic in firmware with the help of a simple timer/counter or choose an advanced controller that has integrated hardware PWM capabilities. Combining

CAPACITIVE SENSING and LED LIGHTING (Part 1)

To read the first article in this series, click on the image to the right.

apacitive touch sensing is the very popular technology used to implement intuitive user interfaces (UI) in many electronics applications including smart phones, tablets, LCD/LED TVs, and many others. Touch buttons are fast replacing traditional mechanical buttons. However, unlike mechanical buttons which provide tactile feedback to users by their nature, touch buttons need additional components to provide feedback. LEDs are widely used to provide visual feedback and backlight illumination in touch-based UIs. Some applications require more visual effects apart from simply turning on and off an LED. For example, a laptop may blink the power LED with its brightness gradually increasing and then gradually decreasing when the device is in stand-by. This is called the breathing effect. This is one of the many LED effects such as fading and blinking used in devices. These advanced LED effects, when combined with capacitive touch buttons, improve the aesthetics and the user experience of the system. It’s often desirable to implement multiple features using a single System-on-Chip (SoC) to reduce the BOM. In this four-part series, we’ll discuss the different aspects of implementing capacitive sensing and LED lighting using a single SoC, including the following topics. We will briefly describe different LED lighting techniques adopted in capacitive sensing-based UI applications using real-world use cases.

Pulse Width Modulation (PWM) is one of the common techniques used to implement LED effects. We will discuss how to select a suitable SoC by analyzing the different schemes of implementing LED effects using PWM techniques. Combining implementation of multiple features in a single SoC invariably poses challenges. It is very important to overcome those challenges for a robust design. We will discuss some common challenges such as crosstalk between LEDs and capacitive sensors, drive strength capability, and LED load transients that cause noise within the capacitive sensing subsystem and how to avoid them. Power consumption optimization is of high importance for any electronic system. We will discuss design considerations for low power consumption for applications requiring LED effects.

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

Lighting Electronics

Firmware-based PWM implementation

A simple firmware implementation requires a timer and an interrupt subroutine (ISR). This timer creates an interrupt for the period equal to every step size of the duty cycle. For example, if the PWM period is 10ms (100Hz) and step size is 1ms (10% duty cycle), the timer will have to interrupt the CPU every 1ms; i.e., Timer Period = Pulse Width/Step Size. Figure 1 depicts the logic in the ISR. PULSE_WIDTH and ON_TIME represent the pulse width and ON time of the PWM in number of steps. For example, PULSE_WIDTH = 5 for a requirement of 5 brightness levels and ON_TIME = 2 for 40% duty cycle. The ISR variable isrVar controls when the output is switched from ON to OFF. This logic can be easily extended to support multiple LED pins with each LED having a separate duty cycle.

Figure 1. Firmware PWM ISR Logic

“THERE ARE TWO WAYS TO IMPLEMENT PWM WITH A MICROCONTROLLER. EITHER IMPLEMENT THE ENTIRE PWM LOGIC IN FIRMWARE WITH THE HELP OF A SIMPLE TIMER/COUNTER OR CHOOSE AN ADVANCED CONTROLLER THAT HAS INTEGRATED HARDWARE PWM CAPABILITIES.”

TECH ARTICLE Hardware-based PWM implementation

Advanced controllers have dedicated hardware blocks to drive PWM. For example, Cypressâ&#x20AC;&#x2122; PSoC4 has a block called TCPWM that implements hardware-based PWM drive. Generally, this is realized using a timer with a compare capability, and the logic is similar to the firmware logic discussed above. The timer will have a compare register along with the period register. The period register is loaded with a value equal to the pulse width and the compare register is loaded with the value equal to the ON time. The timer will have an output that goes high as long as the compare value is greater than the tick value and goes low otherwise. Also the tick value automatically rolls back to zero when it reaches the maximum value (65535 for a 16-bit timer). This output is routed to a port pin, thus driving the LED directly using a hardware block. Table 1 summarizes the differences between firmware-based and hardware-based PWM implementations. In this part, we examined different ways of implementing PWM. In Part 3, weâ&#x20AC;&#x2122;ll explore common challenges faced when designing systems with capacitive sensing and LED lighting, and how to overcome them.

Firmware based vs. Hardware based PWM Implementation Firmware based Implementation

Hardware based Implementation

Low-cost controller with one timer is sufficient

Requires an advanced controller with hardware PWM block

One timer is enough to implement a multi-channel PWM

Typically, only a few PWM blocks are required to fully realize a multi-channel PWM

Free pin assignment

Restricted pin assignment as the hardware blocks usually support fixed pins for PWM drive

Need to serve frequent interrupts, causing CPU overhead. Also, frequency of the interrupts increases with the increase in required brightness levels and number of PWMs controlled

No interrupts, CPU is 100% available for other code

Strict interrupt latency control is required to avoid jitter

Not to worry about interrupt latency

Limitation on the maximum achievable resolution

No limitation (depends on the width of the period and compare register of the timer)

Less accurate PWM control

More accurate PWM control

Not possible to put CPU into sleep during PWM drive, thus drawing more power

Ability to put CPU into sleep, thus drawing less power

Table 1.

Lighting Electronics

INNOVATIVE

LIGHTING from OSRAM

SHINES

Down the Road OSRAM, a leading light manufacturer worldwide, offers an impressive portfolio that ranges from components— including lamps and optoelectronics such as organic lightemitting diodes (OLEDs)—to electronic control gears as well as complete luminaires, light management systems, and lighting solutions. The company’s business activities have been focusing on lighting for over 100 years. In an interview with EEWeb, Dr. Karsten Diekmann, senior manager of product application and engineering for OSRAM OLED, discussed the nature of the OLED applications market and their future. Dr. Diekmann also addressed OLED applications in the automobile industry.

COVER INTERVIEW With its luminaire, called â&#x20AC;&#x2DC;Rollercoasterâ&#x20AC;&#x2122; for its interesting architectural design, OSRAM demonstrates the industry maturity of transparent OLED.

Interview with Dr. Karsten Diekmann, Senior Manager Marketing, Product & Application Engineering OSRAM OLED

Lighting Electronics

Could you please describe OLED technology and how it differs from standard LEDs? LEDs are point light sources based on crystalline inorganic materials. They can be realised in small packages with high luminous intensities. OLEDs are area light sources based on amorphous organic materials. The expression “organic” originates from chemistry and means hydrocarbon based. The large area can be shaped freely, and the visual impression in the switched-off state can be, for example, mirrorlike, transparent, or even curved.

How did OSRAM get started with OLEDs? OSRAM started research on OLEDs back in 1996. In 2006, the effort for development of lighting applications was intensified by establishing an OLED development line followed by a pilot line in 2011. At the last Light + Building trade show in Frankfurt, OSRAM showed

“JUST IMAGINE, A CLASSIC LAMPSHADE BECOMES THE LIGHT SOURCE ITSELF AND DOES NOT NEED TO HIDE THE BULB INSIDE.”

OLEDs from that pilot line for general lighting applications with 65 lm/W at 3,000 cd/m² with 15,000 hours of lifetime (L70). For automotive applications, lifetime values of more than 3000 hours could be reached already under hightemperature cycle conditions.

What new applications or technologies does OLED enable? We are looking into two basic application segments, namely automotive and general illumination. The automotive application segment for the OLED is innovation and style driven, thus the ideal platform to leverage new technologies with new design features. Customised form factors will enable first applications followed by further design options such as curved and transparent lighting surfaces.

What prompted the design of the OSRAM flexible OLED, and what are some more unique applications it can be used in? Flexible OLEDs still need a few years before commercialization. The technical challenges are in the encapsulation technology, which has to withstand

COVER INTERVIEW humidity and mechanical bending stress at the same time. The possibility of applications is vast, such as wearable electronics and specially shaped luminaires. Just imagine, a classic lampshade becomes the light source itself and does not need to hide the bulb inside.

How is the technology progressing, and at what point do you expect to match LED system performance? In 2016 we want to break the 100 lm/W threshold for general illumination applications and fulfill automotive requirements. OLEDs have nearly no thermal and optical losses, thus they would play in the same league as LEDs on system level.

What are the challenges preventing greater OLED adoption, and how do you expect the market to shift in the next 3 to 5 years and in the next 10 years? Looking at various market studies, a great range of revenue expectations for OLED lighting can be observed. The market development depends on many details and acceptance factors such as meeting the performance and cost roadmaps or sorting out standardization issues. We believe that OLED can be the second pillar of solid-state lighting (besides LED). We expect the first automotive projects in 2016. General lighting projects were limited to luxury and premium design projects with extremely low volume so far. This situation might change just slightly in alignment with improved cost position.

“OLED CAN BE THE SECOND PILLAR OF SOLID-STATE LIGHTING.”

Karsten Diekmann gained his PhD at the University of Paderborn in 1997. In his thesis, he investigated phase-transition phenomena in liquid crystal systems. After finishing a trainee program at Ciba Specialties (now BASF) in 1998, he joined the display competence team at Mannesmann VDO (now Continental) in Babenhausen near Frankfurt. With his experience in liquid crystals, he strengthened the company’s position as market leader in driverinformation systems. Responsible for new technologies as well, he was immediately fascinated when he got in contact with OLED display technology. Thus, in 2001 he decided to join OSRAM Opto Semiconductors in Regensburg as an application engineer in this emerging technology field. He was involved in the very early development stages to make OLEDs usable for lighting applications (e.g. in the pioneering OLLA project starting in 2004). Since 2008, he has been leading OSRAM’s activities for product and application engineering in the OLED segment. In addition, he took over the OLED marketing responsibility in 2011.

Lighting Electronics

OSRAM Approaches Market Maturity for

OLEDs in Cars

OSRAM unveils product strategy toward serial production In another step to innovate the future of automotive lighting, OSRAM made clear at last year’s Frankfurt International Motor Show that substantial progress was made in the development of organic LEDs (OLEDs) to be used in automotive applications. “In 2016 at the latest, we expect to see OLEDs used in series production of new vehicles,” says Ulrich Eisele, CEO of OSRAM OLED GmbH. Temperature stability, the most significant obstacle to series production, was increased at the critical storage level of 85°C, for a record duration of more than eight thousand hours. “After a further year of research, the remaining obstacles regarding serial production are small,” says Eisele. OLEDs are surface light sources and therefore perfect for the use in applications such as rear light fixtures. Transparent OLEDs also offer new design possibilities for those applications. In Paris of 2013, OSRAM unveiled a first rear-light demonstrator based on transparent OLEDs. This was followed by a successor that meets the requirements for road traffic not only in matters of tail lights, but also in brake light applications.

“THE AUTOMOTIVE APPLICATION SEGMENT FOR THE OLED IS INNOVATION AND STYLE DRIVEN.” These are defined internationally in the standards of the Economic Commission for Europe (ECE). The second demonstrator highlights segmented OLEDs as a special feature. It is possible to divide the homogenous light area into dynamically controllable segments, thereby creating a distinct lighting scenario, for example, by clicking on the door-lock remote control. The OLED rear light fixture has been featured at the International Symposium on Automotive Lighting (ISAL) in Darmstadt, Germany, the Light+Building trade show in Frankfurt, Germany, and the DVN (Driving Vision News) conference in Seoul, Korea.

Lighting Electronics

SHIFT REGISTERS

LED Designs

Reduce Size and Cost in

By Michael Lyons, NXP Semiconductor

TECH ARTICLE

hift registers can help reduce size and bill of materials in designs that use LEDs. By providing input/output expansion, they enable the use of smaller, less expensive microcontrollers. In some cases, the shift register can be used to drive the LED directly and thus eliminate the need for external LED drivers. This adds to the savings and makes it possible to drive a wider variety of LEDs.

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USING SHIFT REGISTERS In designs that use LEDs, shifter registers can be very useful. For instance, if the system includes a seven-segment display, a single indicator, or an array of LEDs that form a grid or panel, a standard 8-bit shift register can be used to allow a low pincount microcontroller to drive multiple LEDs. Figure 1 gives an example. A single 5V 74HC595 shift register, with serial inputs and serial or parallel outputs, provides I/O (input/output) expansion for the microcontroller. Serial data is applied to the serial input of the 74HC595 and clocked in via the input clock. Once the 74HC595 is loaded, the output clock applies the data to the storage register and to the parallel and serial outputs. External drivers, controlled by the 74HC595, then activate the corresponding LEDs.

Figure 1. An 8-bit 74HC595 shift register driving multiple LEDs.

Using the 74HC595 for I/O expansion means that it takes only three microcontroller-unit (MCU) control pins to drive up to eight LEDs. Reducing the number of control pins makes it possible to use an MCU with a lower pin count, and that can yield a smaller, more cost-effective design. Also, because the 74HC595 includes a serial output, several devices can be cascaded together. Figure 2 gives the layout. Now, with the cascading, the same three pins on the microcontroller can be used to control up to 16 or 24 LEDs instead of just eight. The ability to cascade shift registers can reduce the total number of microcontrollers needed in the design, and that can help lower costs and reduce size, too. In some cases, a 5V, 8-bit register like the 74HC595 can be used to drive LEDs directly.

Figure 2. Cascading 74HC595 devices to drive more LEDs.

TECH ARTICLE This works best when the LEDs are specified for relatively low voltage and forward current. LEDs that operate with voltages higher than 6V or require forward current that exceeds 70mA will typically require an external driver. OPEN-DRAIN OUTPUTS Adding open-drain outputs to the shift register creates a single-chip solution that eliminates the need for an external driver. This can yield significant reductions in the bill of materials, since each output of the shift register can drive the LEDs directly. Figure 3 gives the output schematic for one such device, the NPIC6C596A LED driver from NXP, which combines shift-register functions similar to a 74HC595 with a high-voltage (HV) metaloxide-semiconductor field-effect transistor (MOSFET) driver.

Figure 3. Output schematic for shift register with open-drain outputs.

Figure 4 shows the NPIC6C596A used in place of the 74HC595. Making this replacement eliminates the need for external drivers, creating a design that is more compact and has a lower bill of materials. NPIC6C devices have open-drain outputs that are tolerant to 33V. Each output is designed to sink 100mA and there is no limit on ground current. All the outputs can actively sink 100mA simultaneously. The outputs include currentlimiting circuitry, which sets a 250mA maximum on the sinkable current, and each output also includes thermal protection. Having these protections means the NPIC6C596A device can be used to drive a wider range of LEDs than the 74HC595, including LEDs that operate at higher voltages and with higher forward current.

Figure 4. NPIC6C596A replacing 74HC595.

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PROTECTION FEATURES Figure 5 shows the behavior of the currentlimiting circuitry on the open-drain outputs of the NPIC6C596A. The circuitry limits the maximum current each output can sink. As the drain voltage increases, the drain source current decreases. This protects the outputs and the components they are driving. At 25°C, the output clamp is typically activated when the drain source current is 250mA. Figure 6 shows how the open-drain outputs of the NPIC6C596A provide thermal protection. The clamp current is inversely proportional to temperature. As the temperature increases, the output resistance increases, thus limiting the drain source current and preventing damage to the output and the components it drives. At 25°C, the output typically limits the drain source current to 120mA.

“The ability to cascade shift registers can reduce the total number of microcontrollers needed in the design, and that can help lower costs and reduce size, too.”

Figure 5. Current-limiting behavior in NPIC6C596A.

Figure 6. Thermal protection in NPIC6C596A.

TECH ARTICLE

MULTIPLE OPTIONS Table 1 shows the NPIC6C LED drivers available from NXP. The NPIC6C596 and the NPIC6C596A are 8-bit solutions, while the NPIC6C4894 is a 12-bit solution. All include a serial output for cascading. Data is propagated through the shift register on the rising edge of the input clock. With the NPIC6C595 and the NPIC6C4894, the same rising edge is used to clock data to the serial output QS. The NPIC6C596 and NPIC6C596A delay the serial output to the next falling edge of the input clock. The delay provides a longer data hold time, which improves timing margin and makes it easier to cascade many shift registers.

“The NPIC6C596A device can be used to drive a wider range of LEDs than the 74HC595, including LEDs that operate at higher voltages and with higher forward current.”

Type number

Format

Supply voltage (V)

fmax (MHz)

Tamb (°C)

QS clock

Packages

NPIC6C595

8-bit

4.5 to 5.5

-40 to +125

Rise

SO16, TSSOP16, DQFN16

NPIC6C596

8-bit

4.5 to 5.5

-40 to +125

Fall

SO16, TSSOP16, DQFN16

NPIC6C596A

8-bit

2.3 to 5.5

-40 to +125

Rise

SO16, TSSOP16, DQFN16

NPIC6C4894

12-bit

4.5 to 5.5

-40 to +125

Rise

SO20, TSSOP20, DQFN20

Table 1. Rise to Fall for NPIC6C596A.

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The NPIC6C596 and NPIC6C4894 can be used between 4.5 and 5.5V, making them suitable for 5.0V control logic interfaces. The NPIC6C596A can be used from 2.3 to 5.5V, so it can be used with 5.0, 3.3, and 2.5V control logic interfaces. All NPIC6C devices operate from -40 to +125째C and with an input clock frequency of at least 10MHz. NPIC6C LED drivers are available in industrystandard small outline (SO) and (thin-shrink small outline package) TSSOP packages, as well as the space-saving depopulated verythin quad flat-pack no-leads (DQFN) leadless package, which is up to 76 percent smaller than a TSSOP and 40 percent smaller than a quad-

Package Suffix

flat no-leads (QFN). DQFN packages also include a heat sink and are the packages of choice for space-constrained applications that use higher currents. Automotive variants are also available. SMALLER AND LESS EXPENSIVE When LEDs are part of the design, shift registers make it possible to use a smaller, less expensive microcontroller. Standard 8-bit shift registers like the 74HC595 are available from a number of suppliers, including NXP. Shift registers that are equipped with open-drain outputs, like the NPIC6C series from NXP, go a step further, because they eliminate the need for external LED drivers.

16-pin

20-pin

20pin

Package

SOT109-1

SOT403-1

SOT763-1

SOT163-1

SOT360-1

Width (mm)

6.00

6.40

2.50

10.30

6.40

Length (mm)

9.90

5.00

3.50

12.80

6.50

Height (mm)

1.75

1.10

1.00

2.65

1.10

Pitch (mm)

1.27

0.65

0.50

1.27

0.65

Table 2. Package options for NPIC6C LED drivers.

More about the NPIC6C series can be found at: http://www.nxp.com/products/logic/family/NPIC/#overview

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