Holtek HT7937 - LED Backlight Driver

10/02/2008

With the continually decreasing costs of LEDs, white light LED applications are witnessing a great expansion. In light of these developments, and aimed specifically at the backlight application area, Holtek will be releasing a series of new LED driver devices, the first of these being the HT7937 for serially connected LEDS.

The HT7937 provides a high drive voltage which is able to drive up to 5 LEDs in series. Using LEDs in series means that the individual LED currents are identical resulting in the same generated illumination level from each LED. As the feedback voltage is fixed at 95mV, by using a 4.7 ohm feedback resistor, an LED current of 20mA can be setup. By using a low value 95mV feedback voltage, the power consumed in the resistor is kept to a minimum which helps to achieve a high conversion efficiency of up to 84%.

As for the internal voltage protection circuits, should the LEDs be damaged and the voltage feedback signal be open circuited, the generated output voltage will be limited to the protection voltage value to protect the device. The HT7937 operates at a frequency of 1.2MHz, allowing designers to utilise inductors and capacitors with smaller footprints, reducing demands on the PCB real estate. In using a SOT26 package type, the device is suitable for use in a wide range of portable products such as mobile phones, digital cameras, audio/multi-media products etc.