A digital soft-start circuit for buck DC-DC converter

Abstract

In this paper, a soft-start circuit is present to prevent the large surge current and overshoot voltage to improve the reliability of the DC-DC converter. The proposed structure generates the step-shaped soft-start voltage through 7 bits DAC. Combining with the PWM comparator, the soft-start circuit controls the system duty cycle directly. The mechanism of the soft-start acts as the high clamp function, which eliminates the need of the clamp circuit. A DC-DC buck converter with the proposed soft-start circuit is based on a 0.4 μm BCD process for verification Hspice simulation shows that under the condition with 3.6 V input voltage, 1.8 V output voltage and 600 mA load current, the soft-start is achieved. After 1.2 ms of the soft-start time, the operation turns to stable.