A fast novel soft-start circuit for peak current-mode DC—DC buck converters

A fully integrated soft-start circuit for DC—DC buck converters is presented. The proposed high speed soft-start circuit is made of two sections: an overshoot suppression circuit and an inrush current suppression circuit. The overshoot suppression circuit is presented to control the input of the error amplifier to make output voltage limit increase in steps without using an external capacitor. A variable clock signal is adopted in the inrush current suppression circuit to increase the duty cycle of the system and suppress the inrush current. The DC—DC converter with the proposed soft-start circuit has been fabricated with a standard 0.13 μm CMOS process. Experimental results show that the proposed high speed soft-start circuit has achieved less than 50 μs start-up time. The inductor current and the output voltage increase smoothly over the whole load range.