40 nm CMOS white LED driver for mobile display application

Abstract

An on-chip boost DC-DC converter used in White LED (WLED) drivers & controller ICs for mobile applications is presented in this paper. The boost controller provides a programmable average current to a string of up to six LEDs in series A Constant On-Time (COT) valley-current-mode control loop sets the duty cycle by controlling the off period. This converter is designed with a 40 nm standard CMOS process. Experimental results show that the converter can operate with supply voltage from 2.5 V to 4.3 V, which is suitable for single-cell lithium-ion rechargeable battery supply applications, and boost input voltage up to 21 V for lighting WLED displays. The output current can be programmed from 0.5 mA to 21 mA with a 100 nF off-chip capacitor and a 10 μH off-chip inductor. The power efficiency is greater than 78% for a 21.5 mA load current, and achieves 84 % at about 3.5 V battery voltage.