A novel start-up circuit for boost DC-DC converter with synchronous power-switch current-limit

In order to suppress the inrush current at start-up stage for synchronous boost converters, a novel start-up circuit with synchronous power-switch current-limit is proposed. A current sensing circuit with high accuracy for the synchronous power-switch and a linear feedback loop of current-limit are designed. The current-limit function is only enabled at start-up stage. In addition, the body node of the synchronous power-switches is supplied by a back-to-back diode structure from the input voltage and the output voltage, respectively, which effectively avoids the conduction of parasitic body diode on synchronous power-switches. The proposed technique has been successfully applied to a synchronous boost converter with 0.18μm 5 V CMOS process successfully. The experimental results show that the proposed method can effectively suppress the inrush current through synchronous power switch, and the output voltage rises smoothly without overshot.