On-Chip Compensated Wide Output Range Boost Converter with Fixed-Frequency Adaptive Off-Time Control for LED Driver Applications

An on-chip compensated wide output range boost converter with fixed-frequency adaptive off-time current-mode control is presented. The small signal characteristic of the boost converter with current-mode control is reviewed, and an adaptive current sensing technique is proposed to reduce the variation of phase margin at different output voltages. On-chip compensation is achieved with a Type II compensator. Adaptive off-time control is adopted for its fast response and no need for slope compensation, while its disadvantage of varying switching frequency is eliminated by the proposed off-time generator. The IC controller was fabricated in a 0.5 mu m 2P3M BCD 40 V process. Measurement results confirm that an output range of 5.5 V similar to 36 V with an input voltage of 5 V is achieved. The switching frequency is fixed at 1 MHz with a variation of +/-1%. The measured peak efficiency and maximum output power are 92.9% and 8.6 W, respectively. For a load step of 200 mA using a 3.3-mu H inductor and a 20-mu F output capacitor, overshoot and undershoot of the load transient responses are smaller than 1% of the output voltage.