/a>LED” title=”LED”>LED” title=”LED”>LED backlight driver, the current control accuracy between each WLED is within ±1.5%, the input voltage range is 4.5~26V, and it provides 8 channels LED current interface, the operating frequency can be selected as 500kHz or 1MHz, the rated maximum current of the built-in power NMOS is 2.2A, and it provides WLED string open circuit and open circuit protection. Other protection mechanisms include over-voltage protection, current-limiting protection, over-temperature protection, and low-voltage lockout. This article introduces the main features, block diagram, typical application circuit diagram and PCB layout of the HT7945.

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 4×4 tiny footprint package type

HT7945 main features:

• 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 application:

• LED backlights for notebook and tablet PCs

Figure 1. HT7945 block diagram

Figure 2. Typical application circuit diagram of HT7945

Figure 3. HT7945 Evaluation Board PCB Layout (Top Layer)

Figure 4. HT7945 Evaluation Board PCB Layout (Bottom Layer)
For details, see:
http://www.holtek.com.cn/PDF/Power_Management/HT7945v100.pdf