Maxim MAX17129低成本6串白光LED驱动方案

关键词： LED驱动 , MAX17129 , Maxim , 白光

Maxim公司的MAX17129/MAX17149是高效率白光LED（WLED）驱动器，适合中小型LCD屏采用LED作为光源。工作电压3-26V，可驱动六串多个LED串联的LED串，串间电流匹配度在±2%内，支持PWM和混合调光模式，调光比100：1，PWM调光模式的调光频率100Hz到25kHz，LED电流从10mA到45mA可调，具有LED开路和短路保护以及输出过压保护，主要用用在笔记本电脑和平板电脑，显示器，汽车系统和手持终端。本文介绍了MAX17129/MAX17149主要特性，方框图，典型工作电路图以及MAX17129评估板主要特性，电路图，材料清单和PCB布局图。

MAX17129/17149：Low-Cost, 6-String WLED Drivers with Quick-PWM Step-Up  Converters

The MAX17129/MAX17149 are high-efficiency drivers for white LEDs. They are designed for small- to mediumsized LCDs that employ an array of LEDs as the light source. An internal switch step-up controller with Quick- PWMK drives the LED array, which can be configured for up to 6 strings in parallel and either 11 LEDs (MAX17129) or 6 LEDs in series (MAX17149) per string. Each string is terminated with a ballast that achieves Q2% currentregulaTIon accuracy, ensuring even LED brightness and provides an adjustable 10mA to 45mA full-scale LED current. The devices have a wide input voltage range of 6V to 26V. The MAX17129 integrates an LDO to simplify applicaTIons that have a single high-voltage supply. The devices also feature a low-input-voltage mode for applicaTIons that have a 3V to 5.5V supply voltage.

The devices support both PWM and hybrid dimming mode. In PWM dimming mode, the external PWM signal directly controls the brightness of LEDs. The dimming frequency ranges from 100Hz to 25kHz with 400ns minimum on-TIme. In hybrid dimming mode, the LED current amplitude can be adjusted to 25% of full-scale LED current to improve system efficiency when brightness is low.

The devices have multiple features to protect the controller from fault conditions. Separate voltage-feedback loops limit the output voltage to safe operation. The open and short-LED detection shuts down the faulty string while keeping other strings operating normally.

The devices feature cycle-by-cycle current limit on the internal switch to provide consistent operation and softstart capability. If the devices are in current-limit condition, the step-up converter is latched off after an internal timer expires. A thermal-shutdown circuit provides another level of protection and prevents ICs from damage.

The ICs’ step-up controller features an internal 0.25I (typ), 48V (max) power MOSFET with lossless current sense and accurate cycle-by-cycle current limit. The Quick-PWM control architecture provides fast load-transient response without requiring an external loop compensation component, simplifies the external circuitry, and saves board area. The Quick-PWM control scheme has constant off-time and adjustable pseudo-fixed frequency, which enables a wide variety of applications that can trade off component size for operating frequency. Low feedback voltage at each LED string (275mV typ at 20mA LED current) helps reduce power loss and improve efficiency.

The ICs are available in a 16-pin, thin QFN package with 0.5mm lead spacing. The package is 3mm x 3mm with a maximum thickness of 0.8mm for ultra-thin LCD panel design.

MAX17129/MAX17149主要特性：

3V to 26V Input Supply Voltage

Up to Six Parallel Strings of Multiple Series-Connected LEDs

Step-Up Regulator with Quick-PWM Control Scheme

Two-Level Selectable Switching Frequency

0.25I Internal HV Power MOSFET (48V max)

Low String Feedback Voltage: 275mV at 20mA LED Current

Full-Scale LED Current Adjustable from 10mA to 45mA

±2% Current Regulation Accuracy Between Strings

Support PWM and Hybrid Dimming Mode

100:1 Dimming Ratio

100Hz to 25kHz Dimming Frequency for PWM Dimming Mode

Open and Short LED Protection

Output Overvoltage Protection

Small 16-Pin, 3mm x 3mm Thin QFN Package

MAX17129/MAX17149应用：

Notebook, Subnotebook, and Tablet Computer

Displays

Automotive Systems

Handy Terminals

2011-11-3 13:21:58 上传

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图1。MAX17129/MAX17149方框图

2011-11-3 13:21:58 上传

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