A CMOS hysteretic DC-DC buck converter with a low output ripple voltage

This paper describes a CMOS hysteretic DC-DC buck converter with a low output ripple voltage and 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 μm BCDMOS process and die size was 1.37mm × 1.37mm. The measurement results showed that the proposed circuit received the input of 3.7V and generated output of 1.2V with the output ripple voltages less than 20mV under load currents of 100~400mA at the fixed switching frequency of 2MHz. The maximum efficiency of the proposed hysteretic buck converter was measured to be around 93%.