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This paper presents a white LED backlight driving chip with 3-bit dimming controller and duty-variable power MOS which can be modified with the voltage-mode pulse width modulation (PWM). In the proposed chip, a 3-bit digital-to-analog converter (DAC) and a ramp generator are used to provide eight pulses with variable width through a voltage comparator. Thus, a 3-bit dimming controller can be implemented with those duty cycles for white LED backlight driver. In this paper, the proposed chip is designed and implemented with TSMC 0.35 μm 2P4M CMOS process. The simulation results of the switching DC-DC boost converter show that the output voltage, output current, and chip area are 20 V, 20 mA, and 1.45×1.28 mm2, respectively, at the supply voltage of 3.7 V. The output voltage of 20 V can drive five white LEDs because that a white LED works with a driving voltage of 3.5 V and a driving current of 20 mA.