A novel compact soft-start circuit with internal circuitry for DC-DC converters

A novel internal soft-start circuit with simple topology for DC-DC buck converters is presented. It is implemented by controlling the output of error amplifier to make switch current limit increases in steps without using external capacitor, which reduces the component cost, saves board space and benefits for portable applications. This circuit is designed on the basis of Hynix 0.5 mum CMOS process, and its performance has been verified by Hspice simulation and measurement results. Avoiding the inrush current and overshoot vloltage, the IC starts up in 4 steps in 1.6 ms with input voltage of 3.6 V, output voltage of 1.8 V, output capacitor of 22 muF and load current of 1.1 A.