原标题：Holtek HT7945平板电脑WLED背光驱动方案

　　盛群半导体(Holtek)公司的HT7945是用于笔记型计算机及平板计算机显示器WLED背光的驱动器,各WLED之间的电流控制精度在±1.5%之内,输入电压范围为4.5~26V,提供8信道LED电流接口,工作频率可选择为500kHz或1MHz,内置的功率NMOS的额定最大电流为2.2A,提供WLED串开路及断路保护。其它的保护机制有过电压保护、限流保护、过热保护及低电压锁定等.本文介绍HT7945主要特性,方框图,典型应用电路图和PCB布局图.

　　The HT7945 is a high efficiency DC-DC controller which can drive multiple WLEDs connected in a series/parallel configuration. The device has a wide input voltage, ranging from 4.5V to 26V, and an adjustable 15mA to 30mA WLED current, setup using an external resistor. In total, the device can support up to 88 WLED.

　　In addition, eight current sink regulators provide ±1.5% high precision current matching between strings. The brightness can be adjusted by an external PWM signal with frequency up to 20kHz. Once an open/short string is detected, that string is disabled while the other strings continue to operate normally.

　　Other protection includes soft-start, under voltage lockout, programmable over voltage protection, switch current limit and thermal shutdown.

　　The HT7945 is supplied in a QFN 24 pin 4x4 tiny footprint package type

　　HT7945主要特性:

　　• Max input voltage: 26V

　　• Integrated Power Mosfet

　　• Output voltage up to 40V driving 11 series LEDs – LED Vf(max)=3.5V per string – absolute max rating up to 44V

　　• Channel Phase Shift PWM Dimming

　　• Drives up to 12 LED strings under Vf(max.)=3.3V condition

　　• Low string feedback voltage: 0.8V at 20mA LED current

　　• Switching frequency: 500kHz/1MHz

　　• 8-string constant current output

　　• LED current adjustable from 15mA to 30mA

　　• ±1.5% current matching between strings

　　•PWM dimming control

　　•1% minimum dimming duty-cycle at 2kHz

　　•Integrated soft start function

　　•LED failure detection: open and short circuit

　　•Capacitor type: ceramic

　　•Protection: OVP, OTP, UVLO, SW current limit

　　•Small 24-pin outline package: 4mm×4mm, thin QFN type

　　HT7945应用:

　　• LED backlights for notebook and tablet PC

　　图1.HT7945方框图

　　图2.HT7945典型应用电路图