The HT7955 is a high efficiency DC-DC controller drives a number of WLEDs connected in series/ parallel configuration and has a wide input voltage range from 10V to 26V, and adjustable 60mA to 80mA WLED current by external resistor. In total, the device can support up to 80 WLED.

In addition, six current sink regulators provide ±2.5% high precision current matching between strings. The brightness can be adjusted by external PWM up to 2kHz. Once an open/short string is detected, the string is disabled while other strings operate normally.

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

The HT7955 is packaged with a tiny footprint package of 48-Pin 7x7x1.0mm TQFP-EP package.

HT7955主要特性:

• Allowable max input voltage: 26V

• Built-in Power MOSFET

• Output voltage up to 40V driving 10 series LEDs – LED Vf(max)=3.5V per string – absolute max rating up to 44V

• Channel Phase Shift PWM Dimming

• Direct PWM Dimming without Phase Shift

• Operate up to 11 strings LED at Vf(max.)=3.3V condition

• Low string feedback voltage: 0.5V at 80mA LED current

• Switching frequency: 200kHz/400kHz

• 8-string constant current output

• LED current adjustable from 60mA to 80mA

• ±2.5% current matching between strings

•Dimming control using PWM

•1% minimum dimming duty-cycle at 2kHz

•Built- in Soft start

•LED failure detection: open and short circuit

•Capacitor type: ceramic

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

HT7955應用:

• LED backlights for LCD monitor and LCD TV

圖1.HT7955框圖

圖2.HT7955典型應用電路

圖3.HT7955 PCB布局圖

詳情請見:

http://www.holtek.com.cn/PDF/Power_Management/HT7955v100.pdf