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盛群半導(dǎo)體(Holtek)公司的HT7945是用于筆記型計算機(jī)及平板計算機(jī)顯示器WLED背光的驅(qū)動器,各WLED之間的電流控制精度在±1.5%之內(nèi),輸入電壓范圍為4.5~26V,提供8信道LED電流接口,工作頻率可選擇為500kHz或1MHz,內(nèi)置的功率NMOS的額定最大電流為2.2A,提供WLED串開路及斷路保護(hù)。其它的保護(hù)機(jī)制有過電壓保護(hù)、限流保護(hù)、過熱保護(hù)及低電壓鎖定等.本文介紹HT7945主要特性,方框圖,典型應(yīng)用電路圖和PCB布局圖. 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應(yīng)用: • LED backlights for notebook and tablet PC 
圖1.HT7945方框圖
圖2.HT7945典型應(yīng)用電路圖
圖3.HT7945評估板PCB布局圖(頂層)
圖4.HT7945評估板PCB布局圖(底層) 詳情請見: 
HT7945v100.pdf
(2.58 MB)
來源：網(wǎng)絡(luò) |
