An efficient fast response hysteretic buck converter suitable for mobile application is proposed. The problems of large output ripple and difficulty in using of small power inductor that conventional hysteretic converter has is improved by adding PLL (Phase Locked Loop) structure. The circuits are implemented by using Dongbu 0.35um BCDMOS process. The settling time of charge pump output is less than 6us and output voltage overshoot is 2ImV when load current changes from 50mA to 500mA. The efficiency is 90-95% under 50-S00mA load condition and output voltage is 1.2mV with 5.5mV ripple voltage.

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This paper describes a CMOS hysteretic DC-DC buck converter with a constant switching frequency for mobile applications. The inherent problems of a large output ripple voltage that the conventional hysteretic DC-DC buck converters has faced have been resolved by using the proposed DC-DC buck converter which employed a ramp generator circuit to be able to increase a switching frequency. The proposed architecture enables the settling response time of charge pump circuit within the converter to become less than 6us suitable for mobile applications. The proposed DC-DC buck converter was implemented by using 0.35 um BCDMOS process and die size was 1.37 mm x 1.37 mm. The measurement results showed that the proposed circuit received the input of 3.7 V and generated output of 1.2 V with the output ripple voltages less than 20 mV under load currents of 100~400 mA at the fixed switching frequency of 2 MHz. The maximum efficiency of the proposed hysteretic buck converter was measured to be around 93%.