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1 LP5520,LP5521,LP5522,LP55281???????????????????????? Literature Number: ZHCA408

POWER designer Expert tips, tricks, and techniques for powerful designs No. 119 Feature Article...1-7 RGB LED Driver Generates True White Backlighting...2 LED Driver Offering True Linear Dimming.

2 POWER designer Expert tips, tricks, and techniques for powerful designs No. 119 Feature Article RGB LED Driver Generates True White Backlighting...2 LED Driver Offering True Linear Dimming...4 Fully Integrated Flash LED Driver...6 Power Design Tools...8 Color-Management LED Drivers Have a Bright Future By Tomi Koskela, Applications Engineer LED Brightness POWER SAVE Driver IC Current Consumption Ramp Down POWERSAVE Ramp Up Time ma μa Area = Average Current Consumption Figure 1. Automatic Power-Save-Mode Operation in the LP5521 LED Driver Time Introduction Color LEDs are becoming more and more popular in portable consumer devices such as mobile phones, portable media players, and gaming and navigation devices. They are commonly used for indication lights, which could be an RGB LED where the color changes according to the event such as Short Message Service (SMS) or incoming calls. These types of LEDs can be driven in various ways such as LED drivers, General Purpose Input/Output (GPIO) pins on the Power Management Unit (PMU), or advanced Lighting Management Unit (LMU). One area that RGB LEDs have been used heavily is for personalizing handsets with keypad lighting, fun lighting, and phone cosmetics. RGB LEDs also can be used for display backlighting. Increases in the RGB-LED count on mobile phones create challenges for the LED drivers as well. The most common challenges in driving color LEDs in portable devices are power consumption, control interface/programmability, EMI, overall solution size, and system cost. Two key areas driving color LEDs in portable devices warrant detailed discussion: indicator and cosmetic lighting, and display backlighting. NEXT ISSUE: Switching Regulators for Space-Constrained Apps

3 RGB LED Driver Generates Highly Efficient True White Backlighting LP5520 Provides Innovative, Easy-to-Use, Instant Color Gamut Improvement for Small Format Displays D V 5-20V + C VDDA C VDDD C IN C OUT - V LDO V DDA V DDD SW C VLDO S1_IN S2_IN ADC Calibration Memory BOOST FB MCU with I 2 C or SPI C VDDIO 100 nf NRST SS/SDA SCK/SCL SI/A0 SO IFSEL V DDIO PWMR PWMG PWMB BRC SPI/I 2 C Interface LP55XX Color and Brightness PWM Logic LP5520 LED Drivers GND ROUT GOUT BOUT V LDO LM 20 Features Temperature compensated LED intensity and color Individual calibration coefficients for each color Color accuracy ΔX and ΔY % NTSC color gamut, brighter color, better picture quality User programmability for effects, aging, dimming PWM control inputs for each color NEW! NEW! NEW! NEW! Product Description Packaging LP5520 RGB Backlighting LED driver with integrated white balance compensation microsmd-25 LP5521 Programmable, low power, 3-channel LED driver microsmd-20, LLP-24 LP5522 Autonomous single LED controller with one wire interface microsmd-6 LP5526 Lighting Management Unit with high voltage boost converter with up to 150 ma serial flash LED driver microsmd-25 LP5527 LED driver for camera flash and 4 LEDs with I 2 C programmability, LED connectivity, test, and microsmd-30 audio synchronization LP channel LED driver with audio sync, LED connectivity test and independent PWMS/PWMS blinking cycles microsmd-36 Ideal for navigation systems, mobile phones, medical devices, and other portable devices For FREE samples, datasheets, and more information on these products, go to: led.national.com 2

4 POWER designer Color-Management LED Drivers Have a Bright Future Color Indicator LEDs and Cosmetics Lighting in Portable Devices New features in mobile phones and most other consumer portable devices are power dependent. Display backlighting and LEDs overall consume considerable power in handheld devices; therefore, power savings with LED driving is critical. Most of today s new LED drivers are focused particularly on improving the overall power efficiency. The conventional way of driving an indicator LED is with simple current sinks, or with some GPIO pins. These types of LED-driving methods require application-processor control each time the LED is activated. An example application is the indicator LED blinks when an SMS message arrives. When the application processor is required to wake up each time the light effect occurs, the power consumption due to this lighting effect adversely affects battery life. For a power-conscious, simple indicator-led driver, it is ideal to program the blinking sequence to the driver and leave the sequence running without application-processor control. This way the processor can be in sleep mode when the device is not in use while the LED driver handles the blinking sequences itself. When a simple on/off control is required with a single, low-forward-voltage color LED, a step-up DC-DC converter is not necessary and the overall power consumption is further reduced. This type of LED driver can be made extremely small and requires a minimal number of external components, or perhaps none at all. Programmable Lighting Sequences Provide Further Power Savings The ability to control lighting sequences can improve the power-saving capability on mobile devices. An example of a device with this capability is the LP5522 LED driver from National Semiconductor. Blinking sequences are trained to the LP5522 driver with a single-wire interface. After a training command, the driver can repeat the sequence without external control. The LED current can be adjusted with an external resistor while the default current without the resistor is 5 ma. The size of the LP5522 device is 1.2 mm x 0.8 mm x 0.6 mm and the LED is the only external component, making this small and reduced BOM solution ideal for space-constrained and system-cost-sensitive portable applications. When LEDs with higher forward voltage are used, the single-cell Li-Ion battery voltage is not always sufficient to drive the LEDs. In this case, a step-up DC-DC converter is required. A step-up converter can be either capacitive (charge-pump or switched capacitor) or inductive (magnetic boost). Today, a charge-pump converter is used in driving low-voltage parallel-led drivers, and a magnetic-boost converter is used in high-voltage serial-led drivers. For complex lighting sequences such as smooth transitions between different colors, a sophisticated control method is required besides a simple enablecontrol pin. An I 2 C-control bus is widely used in many portable devices as it provides greater flexibility for controlling an LED driver via only two wires. Usually there are other components, for example a camera module, using the same bus. Therefore, LED driving should not use all of the I 2 C bandwidth. Controlling the LED brightness in real time creates considerable I 2 C traffic. A new charge-pump-based color-led driver, such as National s LP5521 device, allows minimum realtime control by incorporating internal memory for sequencing. Lighting sequences are written to an internal memory after power-up, and an external trigger pin or I 2 C write is used to start the sequences. When the sequence is running, processor control is not required. When the phone is in standby mode, the application processor can be in sleep mode while complex lighting sequences can still be achieved. Sequences can include time delays, ramps, blinking, loops, and sending/receiving trigger signals. power.national.com 3

5 Industry s First LED Driver Offering True Linear Dimming for the Human Eye LM3509 Dual-Output Constant-Current LED Driver Operates at 90% Efficiency 10 μh 2.7V to 5.5V 10 kω 30 ma Per String C IN IN SW OVP C OUT 1 μf 1 μf VIO LM3509 SCL MAIN SDA SUB/FB SET RESET/GPIO GND R SET 8 kω Dual White LED Bias Supply Features 32 Exponentially spaced dimming states with 800:1 LED current ratio Auto-dimming function enables transition from one dimming state to the other at different speeds Integrates OLED power supply 2 independently controlled constant current outputs for main and sub displays Drives 10 LEDs at 30 ma with 0.15% current matching Simultaneously drives 5 LEDs at 20 ma and delivers 21V at 40 ma for OLED power supply I 2 C-compatible programmable brightness control LED Current (% of ILED_MAX) 120% 100% 80% 60% 40% 20% Non-Linear Brightness Steps t STEP * 0% BMAIN or BSUB Code (Decimal) *t STEP is the time between LED current steps programmed via bits RMP0, RMP V IN (V) Ideal for driving LEDs in mobile phones, digital cameras, and navigation system displays Efficiency (%) LEDs 6 LEDS 8 LEDS 10 LEDS For FREE samples, datasheets, and more information on the LM3509, go to: led.national.com 4

6 POWER designer Color-Management LED Drivers Have a Bright Future Reducing Power Consumption in LED Drivers To further decrease power consumption, the LP5521 driver has an automatic power-save-mode operation. The DC-DC converter in the LP5521 device starts up only when the Li-Ion battery voltage is not sufficient enough to supply the LEDs. The LP5521 driver also shuts down other unused blocks when the LEDs are not active and while the sequence is running internally. This significantly decreases the average power consumption. Automatic power-save-mode operation implemented in the LP5521 LED driver can be seen in Figure 1. A charge-pump-based RGB-LED driver such as the LP5521 device requires only four small capacitors. With a small footprint and minimum external components, the total solution size can be as small as 7 mm 2. The small solution height makes it suitable for slim design applications. Also with such a small solution size, it is possible to create a localized rather than centralized solution, meaning that the LED driver is located near the LEDs. This way the PCB routing is much easier, and the EMI is reduced. The LP5521 LED driver has external control pins which are used for synchronizing several drivers, making it possible to achieve very interesting lighting effects. RGB LEDs as Small-Panel Display Backlighting in Portable Devices Typically, small-panel LCD-display backlighting can be achieved with a couple of white LEDs. The problem with white LEDs is that their spectrum is not ideal for photographic reproduction. This is caused by the fact that white LEDs are basically blue LEDs with yellow phosphor on top. The spectrum has two peaks: one at blue, and a second at yellow. A typical white-led versus RGB-LED spectrum can be seen in Figure 2. To filter the right color to each color cell (red, green, blue), color filters are used. Color filters waste some of the power and even after color filtering, the color spectrum passing through the LCD is not ideal. With white-led backlighting, it is possible to get up to 75% of the National Television Standards Committee (NTSC) colors on an LCD display (the red end of the conventional LCD display is especially limited). When RGB LEDs are used for LCDdisplay backlighting, the color reproduction can be adjusted to cover over 100% of the NTSC color gamut which results in brighter color and better picture quality. With optimized color filters, less power is wasted than in white-led backlighting. The structure of an LCD display can be seen in Figure 3. Black Matrix Polarizer Color Filter Substrate Liquid Crystal TFT Thin Film Transistor Array Substrate Polarizer Polychromatic Backlight Color Filter Cell (Red, Green or Blue) Capacitor Figure 3. Structure of an LCD Display Transparent Common Electrode Transparent Pixel Electrode Blue Chip RGB Chips + 1 Phosphor nm nm Emission Wavelength Figure 2. Typical White-LED vs. RGB-LED Spectrum Generating True White Backlighting Through Open-Loop Compensation With RGB backlighting, the LED driver must correct the brightness balance between the primary colors (red, green, and blue) when the LED temperature changes. The LED driver keeps the white point of the RGB backlight adjusted correctly at any operating temperature. Compensation can be either closed loop or open loop. With closed-loop compensation, an optical sensor is used for measuring the power.national.com 5

7 Industry s Smallest, Fully Integrated Flash LED Driver High-Power LED Driver Optimized for Driving Single- and Multiple-Die Flash LED Technologies in Handheld Applications Typical Application Diagram V IN = 3.0V to 5.5V C IN 2.2 µf C 1 C µf 2.2 µf V IN C 1 + C 1 - C 2 + LM2754 V OUT D 1 D 2 D 3 D 4 I F = 800 ma max C 4.7 µf OUT D 1 D 2 D 3 D 4 C 2 - I SET1 I SET2 EN T/F TX SEL GND R SET1 R SET2 TDK: 2.2 µf - C1608X5R1C µf - C2012X5R1C475 LM2754 Features Total solution size without LED < 28 mm 2 Time-out circuit limit flash duration to 1s, protects LED from over-heating No inductor required True shutdown output disconnect <1 µa shutdown current TX input ensures synchronization with RF power amplifier pulse Ability to disable one current sink via the SEL pin to accommodate 3-LED flash modules Internal soft-start limits inrush current Available in LLP-24 (4 mm x 4 mm x 0.8 mm) packaging Efficiency (PLED/PIN %) Efficiency vs. Input Voltage 100 ma 200 ma 400 ma 800 ma I D1-4 tied together LED = PWF Input Voltage (V) Ideal for camera flashes for mobile phones and flashes for digital still cameras For FREE samples, datasheets and more information on the LM2754, go to: led.national.com 6

8 POWER designer Color-Management LED Drivers Have a Bright Future white point. With open-loop compensation, the temperature is measured and predefined compensation curves are used to adjust the white point. For RGB backlighting, National offers the LP5520 RGB-LED driver, which is an open-loop-compensated LED driver. The principle of the open-loop color compensation can be seen in Figure 4. With open-loop compensation, an accurate white point is maintained through the operation temperature range. The temperature compensation curves are measured for the actual RGB-LED type used in the application, and these curves are programmed to the chip s internal EEPROM memory. The chip is integrated into the LCD display module, and the module manufacturer programs compensation curves in production. An RGB-LED backlightoptimized color filter is used as well. Temperature Sensor Compensation curves are programmed by display module maker through serial interface to the EEPROM memory ADC Averaging PWM Logic PWM EEPROM Brightness Control (I 2 C/SPI or External PWM) Controlling display brightness with the LP5520 device is similar to that of white-led backlighting. The brightness level is controlled through a SPI or I 2 C bus, and the LP5520 device calculates the actual Pulse Width Modulation (PWM) values according to the compensation curves to maintain the white point. Automatic fade in and out can be used to get a smooth transition. The brightness can be controlled alternatively with an external PWM, and the LP5520 device also has an interface for an T LED Drivers PWM logic reads ambient temperature and compensates R, G, and B LED intensity by changing PWM duty cycle (12-bit resolution) Integrated to One Chip Figure 4. Principle of Open-Loop Color Compensation in the LP5520 LED Driver LEDs ambient-light sensor. Therefore, this color compensation is invisible to the manufacturers, and no special software is needed for controlling the RGB backlight. Fast implementation of an RGB-backlit display to end devices is possible because display vendors have ready-made solutions available. Additional LED Driver Features Because the number of LEDs in handsets and other portable consumer devices is continually increasing, a fast and reliable way to test the connection to each LED is needed. Testing LED connectivity in enddevice production usually requires test points on the PCB for each LED, or optical testing must be used. Incorporating test points to the application PCB is not an easy task considering how tightly packed PCBs in portable devices are today. Furthermore, optical-testing methods are difficult and expensive to implement. With built-in LED-connectivity tests in LED drivers, it is possible to test the connection to each LED through an I 2 C or SPI bus and get accurate results in milliseconds. This makes the production testing very easy to implement and it is also fast and effective. For example, the LED-connectivity test has been integrated into the LP55281, a quad RGB- LED driver. The LED-connectivity test is just one example of a built-in feature which provides extra value to designers. Conclusion RGB LEDs create interesting possibilities to personalize handsets and other portable consumer devices. However, increasing and more versatile use of RGB LEDs in handsets create challenges for the LED drivers. The most significant challenge is how to drive all of these LEDs efficiently in a cost-effective manner and in the smallest solution size. National s new family of lighting-management products provides solutions that meet the challenges of these new lighting trends. For more information, please refer to lighting.national.com. power.national.com 7

Power Design Tools Lighting Solutions Guide For information on National's LED lighting solutions and to download the

com Analog Edge SM App Note National s monthly app note highlight edge.national.

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Box 58090 Santa Clara, CA 95052 Visit our website at: www.national.com For more information, send email to: new.

9 Power Design Tools Lighting Solutions Guide For information on National's LED lighting solutions and to download the guide, visit: led.national.com Analog Edge SM App Note National s monthly app note highlight edge.national.com Reference Designs National s power reference design library provides a comprehensive library of practical reference designs to speed system design and time-to-market. National Semiconductor 2900 Semiconductor Drive Santa Clara, CA Mailing address: PO Box Santa Clara, CA Visit our website at: For more information, send to: new.feedback@nsc.com Don't miss a single issue! Subscribe now to receive alerts when new issues of Power Designer are available: power.national.com/designer Read our Signal Path Designer online today at: signalpath.national.com/designer 2007, National Semiconductor Corporation. National Semiconductor,, and Signal Path Designer are registered trademarks and Analog Edge is a service mark of National Semiconductor. All other brand or product names are trademarks or registered trademarks of their respective holders. All rights reserved

10 重要声明德州仪器 (TI) 及其下属子公司有权在不事先通知的情况下, 随时对所提供的产品和服务进行更正修改增强改进或其它更改, 并有权随时中止提供任何产品和服务客户在下订单前应获取最新的相关信息, 并验证这些信息是否完整且是最新的所有产品的销售都遵循在订单确认时所提供的 TI 销售条款与条件 TI 保证其所销售的硬件产品的性能符合 TI 标准保修的适用规范仅在 TI 保证的范围内, 且 TI 认为有必要时才会使用测试或其它质量控制技术除非政府做出了硬性规定, 否则没有必要对每种产品的所有参数进行测试 TI 对应用帮助或客户产品设计不承担任何义务客户应对其使用 TI 组件的产品和应用自行负责为尽量减小与客户产品和应用相关的风险, 客户应提供充分的设计与操作安全措施 TI 不对任何 TI 专利权版权屏蔽作品权或其它与使用了 TI 产品或服务的组合设备机器流程相关的 TI 知识产权中授予的直接或隐含权限作出任何保证或解释 TI 所发布的与第三方产品或服务有关的信息, 不能构成从 TI 获得使用这些产品或服务的许可授权或认可使用此类信息可能需要获得第三方的专利权或其它知识产权方面的许可, 或是 TI 的专利权或其它知识产权方面的许可对于 TI 的产品手册或数据表, 仅在没有对内容进行任何篡改且带有相关授权条件限制和声明的情况下才允许进行复制在复制信息的过程中对内容的篡改属于非法的欺诈性商业行为 TI 对此类篡改过的文件不承担任何责任在转售 TI 产品或服务时, 如果存在对产品或服务参数的虚假陈述, 则会失去相关 TI 产品或服务的明示或暗示授权, 且这是非法的欺诈性商业行为 TI 对此类虚假陈述不承担任何责任 TI 产品未获得用于关键的安全应用中的授权, 例如生命支持应用 ( 在该类应用中一旦 TI 产品故障将预计造成重大的人员伤亡 ), 除非各方官员已经达成了专门管控此类使用的协议购买者的购买行为即表示, 他们具备有关其应用安全以及规章衍生所需的所有专业技术和知识, 并且认可和同意, 尽管任何应用相关信息或支持仍可能由 TI 提供, 但他们将独力负责满足在关键安全应用中使用其产品及 TI 产品所需的所有法律法规和安全相关要求此外, 购买者必须全额赔偿因在此类关键安全应用中使用 TI 产品而对 TI 及其代表造成的损失 TI 产品并非设计或专门用于军事 / 航空应用, 以及环境方面的产品, 除非 TI 特别注明该产品属于军用或增强型塑料产品只有 TI 指定的军用产品才满足军用规格购买者认可并同意, 对 TI 未指定军用的产品进行军事方面的应用, 风险由购买者单独承担, 并且独力负责在此类相关使用中满足所有法律和法规要求 TI 产品并非设计或专门用于汽车应用以及环境方面的产品, 除非 TI 特别注明该产品符合 ISO/TS 要求购买者认可并同意, 如果他们在汽车应用中使用任何未被指定的产品,TI 对未能满足应用所需要求不承担任何责任可访问以下 URL 地址以获取有关其它 TI 产品和应用解决方案的信息 : 产品数字音频通信与电信放大器和线性器件计算机及周边数据转换器消费电子 DLP 产品能源 DSP - 数字信号处理器工业应用时钟和计时器医疗电子接口安防应用逻辑汽车电子电源管理视频和影像微控制器 (MCU) RFID 系统 OMAP 机动性处理器无线连通性德州仪器在线技术支持社区 IMPORTANT NOTICE 应用邮寄地址 : 上海市浦东新区世纪大道 1568 号, 中建大厦 32 楼邮政编码 : Copyright 2011 德州仪器半导体技术 ( 上海 ) 有限公司

iml88-0v C / 8W T Tube EVM - pplication Notes. IC Description The iml88 is a Three Terminal Current Controller (TTCC) for regulating the current flowi

iml88-0v C / 8W T Tube EVM - pplication Notes iml88 0V C 8W T Tube EVM pplication Notes Table of Content. IC Description.... Features.... Package and Pin Diagrams.... pplication Circuit.... PCB Layout