INNOVATIVE LIGHTING

Interview with Dr. Karsten Diekmann, Senior Manager

Marketing, Product & Application EngineeringOSRAM OLED

from OSRAM Shines Down the Road

Testing that Tells the Truth

Shift Registers Reduce Size and Cost in Designs

July 2014

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READY TO LAUNCH

For the launch of the Tiva C Series Connected LaunchPad, TI has partnered with Exosite, mentioned briefly above, to provide easy access to the LaunchPad from the Internet. The LaunchPad takes about 10 minutes to set up and you can immediately interact with it across the Internet and do things like turn an LED on and off remotely from the website and see the reported temperature as well. It can also display approximate geographic location based on the assigned IP address and display a map of all other connected LaunchPad owners if they are active and plugged-in to Exosite. “In addition, it supports a basic game by enabling someone to interface to the Connected LaunchPad through a serial port from a terminal while someone else is playing with them through their browser. It is basically showing how you can interact remotely with this product and a user even if you are across the globe,” Folkens explained.

START DEVELOPING

The Tiva C Series Connected LaunchPad is shipping now and the price is right; at $19.99 USD, it is less than half the price of other Ethernet-ready kits. The LaunchPad comes complete with quick start and user guides, and ample online support to ensure developers of all backgrounds are well equipped to begin creating cloud-based applications. “We have assembled an online support team to monitor the Engineering-to-Engineering (or E2E) Community,” Folkens said. “Along with this, you also got a free Code Composer Studio Integrated Development Environment, which allows developers to use the full capability. We also support other tool chains like Keil, IAR and Mentor Embedded.

Affordable, versatile, and easy to use, the Tiva Series Connected LaunchPad is well suited for a broad audience and promises to facilitate the expansion of ingenious IoT applications in the cloud. As Folkens concluded, “The target audiences actually are the hobbyists, students and professional engineers. A better way of looking at it is that we are targeting people with innovative ideas and trying to help them get those ideas launched into the cloud.”

CONTENTS

3

Lighting Electronics

4

12

18

22

28

Firmware-based PWM implementationA 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

Hardware-based PWM implementationAdvanced controllers have dedicated hardware blocks to drive PWM. For example, Cypress’ 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, we’ll explore common challenges faced when designing systems with capacitive sensing and LED lighting, and how to overcome them.

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 assignmentRestricted 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.

“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.”

Firmware based vs. Hardware based PWM Implementation

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.

LUXEON 3535 2D LUXEON 3030 2D

“The Philips hue system combines LED lighting,

wireless communication, and smart devices to

enable users to tune both color and luminosity

from anywhere.”

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.

“The hue bulbs are based upon

Philips Lumileds LUXEON Rebel ES series, which

includes the industry leading

lime LED.”

Lighting the Future

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.

Lush GREENS

Individual LED specifications are measured under very controlled environments. In an actual electronics-

manufacturing 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. Let’s have a brief look at the factors that affect LED test results.

TEMPERATUREIn a typical LED datasheet, the specifications will state the LED characteristics at a specified current and with a die temperature of say, 25°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.

Figure 3. Forward voltage versus forward current.

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

DRIVING VOLTAGEIn 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.

ENVIRONMENT AND TEST METHODOLOGYOpen 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.

“In an actual electronics-

manufacturing environment,

application of theory can pose serious

challenges.”

Figure 1. Ambient temperature versus forward current.

Interview withDr. Karsten Diekmann, Senior Manager Marketing, Product & Application EngineeringOSRAM OLED

INNOVATIVE LIGHTING

OSRAM, a leading light manufacturer worldwide, offers an impressive portfolio that ranges from components—including lamps and optoelectronics such as organic light-emitting 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.

from OSRAMSHINESDown the Road

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

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 pin-

count 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.

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.

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) metal-

oxide-semiconductor field-effect transistor

(MOSFET) driver.

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 current-

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

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

Figure 3. Output schematic for shift

register with open-drain outputs.

Figure 4. NPIC6C596A replacing 74HC595.

TECH ARTICLETesting That Tells the TruthExpectations for PCBA-Level LED Tests

TECH ARTICLEBright Future for Philips Lumileds Next-Gen LEDs

TECH ARTICLECombining Capacitive Sensing and LED Lighting

COVER INTERVIEWInnovative Lighting from OSRAM Shines Down the Road

TECH ARTICLEShift Registers Reduce Size and Cost in LED Designs

44

Lighting Electronics

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

TESTING

Expectations for PCBA-Level LED Tests

An in-circuit test system (ICT) measures a component’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 ICT—the tester should be able to test to see if the luminosity and wavelength values are within the ranges indicated on the LED datasheet.

That Tells the Truth

5

TECH ARTICLE

5

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

TESTING

Expectations for PCBA-Level LED Tests

An in-circuit test system (ICT) measures a component’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 ICT—the tester should be able to test to see if the luminosity and wavelength values are within the ranges indicated on the LED datasheet.

That Tells the Truth

66

Lighting Electronics

Individual LED specifications are measured under very controlled environments. In an actual electronics-

manufacturing 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. Let’s have a brief look at the factors that affect LED test results.

TEMPERATUREIn a typical LED datasheet, the specifications will state the LED characteristics at a specified current and with a die temperature of say, 25°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.

Figure 3. Forward voltage versus forward current.

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

DRIVING VOLTAGEIn 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.

ENVIRONMENT AND TEST METHODOLOGYOpen 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.

“In an actual electronics-

manufacturing environment,

application of theory can pose serious

challenges.”

Figure 1. Ambient temperature versus forward current.

7

TECH ARTICLE

7

Individual LED specifications are measured under very controlled environments. In an actual electronics-

manufacturing 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. Let’s have a brief look at the factors that affect LED test results.

TEMPERATUREIn a typical LED datasheet, the specifications will state the LED characteristics at a specified current and with a die temperature of say, 25°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.

Figure 3. Forward voltage versus forward current.

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

DRIVING VOLTAGEIn 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.

ENVIRONMENT AND TEST METHODOLOGYOpen 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.

“In an actual electronics-

manufacturing environment,

application of theory can pose serious

challenges.”

Figure 1. Ambient temperature versus forward current.

88

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.

• 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 boundary-scan 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.

ABOUT THE AUTHORSYang 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 mission-critical railway signal systems.

REFERENCESColor Logical Analysis Approach for LED Testing in Manufacturing

Avago LED Datasheet

Figure 5. Color waveform sampling.

“Open air, semiventilated, or enclosed environments will

cause totally different results for LED wavelength and luminosity

readings.“

“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.”

9

TECH ARTICLE

9

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.

• 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 boundary-scan 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.

ABOUT THE AUTHORSYang 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 mission-critical railway signal systems.

REFERENCESColor Logical Analysis Approach for LED Testing in Manufacturing

Avago LED Datasheet

Figure 5. Color waveform sampling.

“Open air, semiventilated, or enclosed environments will

cause totally different results for LED wavelength and luminosity

readings.“

“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.”

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Light-Emitting Diode (LED) Design Guide

Keep the lights on...Safeguard your LED lighting investment

LED Lighting Protection Design GuideExplore the latest LED lighting industry standards, circuit protection product information, circuit diagrams and links to application notes and videos using this interactive design guide.

Designers of LED residential retrofit lamps and outdoor luminaires will find this a useful resource to quickly find answers to your LED lighting design questions.

Visit the Education Center at www.speed2design.com

Compact, Surge-Tolerant Fuses for Outdoor Lighting

328 and 688 Series Fuses

Open LED Protectors Keep Outdoor LED Strings Shining

PLED6M Series

Boost LED String Reliability, Light Engine Efficiency

PLEDxSW Open LED Protector

Prevent Damage to Outdoor LED Lighting Fixtures

LSP05 & LSP10 SPD Modules

Protecting Technology. Protecting Life.ing Technology. Protecting Life.Protecti

Light-Emitting Diode (LED) Design Guide

Keep the lights on...Safeguard your LED lighting investment

LED Lighting Protection Design GuideExplore the latest LED lighting industry standards, circuit protection product information, circuit diagrams and links to application notes and videos using this interactive design guide.

Designers of LED residential retrofit lamps and outdoor luminaires will find this a useful resource to quickly find answers to your LED lighting design questions.

Visit the Education Center at www.speed2design.com

Compact, Surge-Tolerant Fuses for Outdoor Lighting

328 and 688 Series Fuses

Open LED Protectors Keep Outdoor LED Strings Shining

PLED6M Series

Boost LED String Reliability, Light Engine Efficiency

PLEDxSW Open LED Protector

Prevent Damage to Outdoor LED Lighting Fixtures

LSP05 & LSP10 SPD Modules

Protecting Technology. Protecting Life.ing Technology. Protecting Life.Protecti

1212

Lighting Electronics

By Heidi PluskaContributing Writer

Say 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 bulbs—clunky, mercury-ridden, hard to

dim, and excessively white—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.

Bright Future forPhilips LumiledsNEXT-GEN LEDS

13

TECH ARTICLE

13

By Heidi PluskaContributing Writer

Say 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 bulbs—clunky, mercury-ridden, hard to

dim, and excessively white—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.

Bright Future forPhilips LumiledsNEXT-GEN LEDS

1414

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 down-converted 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

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.”

Demand for Midpower LEDs

Philips Lumileds high-power LED products are the most visible on the market, but midpower LED product-growth 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

“We are one of the few LED companies that does research and development

on phosphors.”

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.”

15

TECH ARTICLE

15

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 down-converted 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

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.”

Demand for Midpower LEDs

Philips Lumileds high-power LED products are the most visible on the market, but midpower LED product-growth 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

“We are one of the few LED companies that does research and development

on phosphors.”

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.”

1616

Lighting Electronics

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.

LUXEON 3535 2D LUXEON 3030 2D

“The Philips hue system combines LED lighting,

wireless communication, and smart devices to

enable users to tune both color and luminosity

from anywhere.”

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.

“The hue bulbs are based upon

Philips Lumileds LUXEON Rebel ES series, which

includes the industry leading

lime LED.”

Lighting the Future

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.

Lush GREENS

17

TECH ARTICLE

17

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.

LUXEON 3535 2D LUXEON 3030 2D

“The Philips hue system combines LED lighting,

wireless communication, and smart devices to

enable users to tune both color and luminosity

from anywhere.”

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.

“The hue bulbs are based upon

Philips Lumileds LUXEON Rebel ES series, which

includes the industry leading

lime LED.”

Lighting the Future

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.

Lush GREENS

1818

Lighting Electronics

CAPACITIVE SENSING

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

In 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.

Combining

(Part 2)

and LED LIGHTING

Pulse Width Modulation (PWM)

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.

To read the first article in this series, click on the

image to the right.

CAPACITIVE SENSING

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

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.

Capacitive 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.

Combining

(Part 1)and LED LIGHTING

19

TECH ARTICLE

19

CAPACITIVE SENSING

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

In 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.

Combining

(Part 2)

and LED LIGHTING

Pulse Width Modulation (PWM)

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.

To read the first article in this series, click on the

image to the right.

CAPACITIVE SENSING

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

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.

Capacitive 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.

Combining

(Part 1)and LED LIGHTING

2020

Lighting Electronics

Firmware-based PWM implementationA 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

Hardware-based PWM implementationAdvanced controllers have dedicated hardware blocks to drive PWM. For example, Cypress’ 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, we’ll explore common challenges faced when designing systems with capacitive sensing and LED lighting, and how to overcome them.

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 assignmentRestricted 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.

“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.”

Firmware based vs. Hardware based PWM Implementation

21

TECH ARTICLE

21

Firmware-based PWM implementationA 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

Hardware-based PWM implementationAdvanced controllers have dedicated hardware blocks to drive PWM. For example, Cypress’ 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, we’ll explore common challenges faced when designing systems with capacitive sensing and LED lighting, and how to overcome them.

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 assignmentRestricted 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.

“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.”

Firmware based vs. Hardware based PWM Implementation

22

Lighting Electronics

Interview withDr. Karsten Diekmann, Senior Manager Marketing, Product & Application EngineeringOSRAM OLED

INNOVATIVE LIGHTING

OSRAM, a leading light manufacturer worldwide, offers an impressive portfolio that ranges from components—including lamps and optoelectronics such as organic light-emitting 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.

from OSRAMSHINESDown the Road

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

COVER INTERVIEW

23

Interview withDr. Karsten Diekmann, Senior Manager Marketing, Product & Application EngineeringOSRAM OLED

INNOVATIVE LIGHTING

OSRAM, a leading light manufacturer worldwide, offers an impressive portfolio that ranges from components—including lamps and optoelectronics such as organic light-emitting 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.

from OSRAMSHINESDown the Road

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

24

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

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 high-temperature 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

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.

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 driver-

information 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.

“OLED CAN BE

THE SECOND PILLAR OF

SOLID-STATE LIGHTING.”

“JUST IMAGINE, A CLASSIC LAMPSHADE BECOMES THE LIGHT

SOURCE ITSELF AND DOES NOT NEED TO HIDE THE BULB INSIDE.”

COVER INTERVIEW

25

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

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 high-temperature 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

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.

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 driver-

information 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.

“OLED CAN BE

THE SECOND PILLAR OF

SOLID-STATE LIGHTING.”

“JUST IMAGINE, A CLASSIC LAMPSHADE BECOMES THE LIGHT

SOURCE ITSELF AND DOES NOT NEED TO HIDE THE BULB INSIDE.”

26

Lighting Electronics

OSRAM Approaches Market Maturity for OLEDs in Cars

“THE AUTOMOTIVE APPLICATION SEGMENT FOR THE

OLED IS INNOVATION AND STYLE DRIVEN.”

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.

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.

http://bit.ly/1jZ9pW5

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Lighting Electronics

DesignsBy Michael Lyons, NXP Semiconductor

Shift 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.

SHIFT REGISTERSReduce Size and Cost in

LED

29

TECH ARTICLE

29

DesignsBy Michael Lyons, NXP Semiconductor

Shift 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.

SHIFT REGISTERSReduce Size and Cost in

LED

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Lighting Electronics

USING SHIFT REGISTERSIn 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 pin-count 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.

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.

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 OUTPUTSAdding 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) metal-oxide-semiconductor field-effect transistor (MOSFET) driver.

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

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

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

Figure 4. NPIC6C596A replacing 74HC595.

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TECH ARTICLE

31

USING SHIFT REGISTERSIn 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 pin-count 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.

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.

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 OUTPUTSAdding 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) metal-oxide-semiconductor field-effect transistor (MOSFET) driver.

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

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

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

Figure 4. NPIC6C596A replacing 74HC595.

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Lighting Electronics

MULTIPLE OPTIONSTable 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.

Table 1. Rise to Fall for NPIC6C596A.

Type number Format Supply voltage (V) fmax (MHz) Tamb (°C) QS clock Packages

NPIC6C595 8-bit 4.5 to 5.5 10 -40 to +125 RiseSO16,

TSSOP16, DQFN16

NPIC6C596 8-bit 4.5 to 5.5 10 -40 to +125 FallSO16,

TSSOP16, DQFN16

NPIC6C596A 8-bit 2.3 to 5.5 10 -40 to +125 RiseSO16,

TSSOP16, DQFN16

NPIC6C4894 12-bit 4.5 to 5.5 10 -40 to +125 RiseSO20,

TSSOP20, DQFN20

Figure 5. Current-limiting behavior in NPIC6C596A.

Figure 6. Thermal protection in NPIC6C596A.

PROTECTION FEATURESFigure 5 shows the behavior of the current-limiting 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.”

“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.”

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TECH ARTICLE

33

MULTIPLE OPTIONSTable 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.

Table 1. Rise to Fall for NPIC6C596A.

Type number Format Supply voltage (V) fmax (MHz) Tamb (°C) QS clock Packages

NPIC6C595 8-bit 4.5 to 5.5 10 -40 to +125 RiseSO16,

TSSOP16, DQFN16

NPIC6C596 8-bit 4.5 to 5.5 10 -40 to +125 FallSO16,

TSSOP16, DQFN16

NPIC6C596A 8-bit 2.3 to 5.5 10 -40 to +125 RiseSO16,

TSSOP16, DQFN16

NPIC6C4894 12-bit 4.5 to 5.5 10 -40 to +125 RiseSO20,

TSSOP20, DQFN20

Figure 5. Current-limiting behavior in NPIC6C596A.

Figure 6. Thermal protection in NPIC6C596A.

PROTECTION FEATURESFigure 5 shows the behavior of the current-limiting 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.”

“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.”

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Lighting Electronics

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 EXPENSIVEWhen 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.

Package Suffix D PW BQ D PW16-pin 16-pin 16-pin 20-pin 20pin

Package SOT109-1 SOT403-1 SOT763-1 SOT163-1 SOT360-1Width (mm) 6.00 6.40 2.50 10.30 6.40

Length (mm) 9.90 5.00 3.50 12.80 6.50Height (mm) 1.75 1.10 1.00 2.65 1.10Pitch (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

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 +125°C and with an input clock frequency of at least 10MHz.

NPIC6C LED drivers are available in industry-standard small outline (SO) and (thin-shrink small outline package) TSSOP packages, as well as the space-saving depopulated very-thin 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-

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