Design of hysteretic buck converter with a low output ripple voltage and a fixed switching frequency in CCM

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 21mV when load current changes from 50mA to 500mA. The efficiency is 90∼95% under 50∼500mA load condition and output voltage is 1.2mV with 5.5mV ripple voltage.