原标题：Diodes AL3157低噪音电荷泵DC转换方案

　　Diodes公司的AL3157是低噪音恒定频率电荷泵DC/DC转换器,采用双模式负载开关(1x)和双(2x)转换,用来驱动白光LED. AL3157能以30mA驱动3路LED,另一路以210mA驱动LED闪光或LED闪光灯,输入电压2.7V-5.5V,关断电流小于1uA,主要用在智能火炬电话LED背光,PDA白光LED背光和背光+火炬照明.本文介绍了AL3157主要特性, 功能方框图和典型应用电路图.

　　The AL3157 is a low noise, constant frequency charge pump DC/DC converter that uses a Dual mode load switch (1x), and doubling (2x) conversion for driving white LEDs. Low external part count (one 1μF flying capacitor and two 2.2μF capacitors at VIN and VOUT) make this part ideally suited for small, battery-powered applications The AL3157 drives 3 channels at up to 30mA for small screen backlighting and an additional channel up to 210mA for LED Flash or LED Flashlight – All from a 2.7V to 5.5V input.

　　The AL3157 uses two control inputs (EN1/2) to enable/disable it and PWM dim the LED current. EN2 controls/PWM dims the backlight LEDs at 30mA per channel and EN1 controls/PWM dims the Flash/Flashlight LEDs at 210mA.

　　Each output is equipped with built-in protection for VOUT short circuit and auto-disable for LED failure conditions. Built-in soft-start circuitry prevents excessive in-rush current during start-up and mode switching. A low-current shutdown feature disconnects the load from VIN to reduce quiescent current less than 1μA.

　　The AL3157 is available in a lead-free, space-saving thermally enhanced 12-pin 3x3mm DFN package.

　　AL3157主要特性:

　　• Dual-Mode 1x and 2x Charge Pump

　　• Up to 300mA drive capability

　　o 3-channel for backlight – 30mA/ch

　　o 1-channel for Flight/light – 210mA

　　• VIN Range: 2.7V to 5.5V

　　• Two simple PWM dimming control inputs up to 50kHz

　　• 1.2 MHz Constant Switching Frequency

　　• Built-In Thermal, Open-Circuit and VOUT short circuit Protection

　　• Soft Start for reducing in-rush current

　　• IQ <1μA in Shutdown

　　• Thermally-Enhanced DFN3030-12 Package: Available in “Green” Molding Compound (No Br, Sb)

　　• Lead Free Finish/ RoHS Compliant (Note 1)

　　AL3157应用:

　　• Smart Touch Phone LED Backlighting

　　• PDA White LED backlighting

　　• Backlighting + Torch light

　　图1.AL3157功能方框图

　　图2.AL3157典型应用电路图