A Compact Digital-Controlled Soft-Start Circuit of DC-DC Switching Converter for Portable Devices

Abstract

This paper proposes a compact digital-controlled soft-start circuit of DC-DC switching converter for portable devices to prevent massive inrush current and overshoot voltage during the start-up period of the converter. Portable devices like virtual reality glasses and portable medical sensors require high stability, portability and low costs. Taking all of them into consideration, the proposed soft-start circuit of DC-DC switching converter for portable devices realizes the soft-start function without off-chip capacitor, large on-chip capacitor or additional resistor, thereby minimizing the implementation area and reducing the cost. The proposed soft-start circuit which is digital-controlled is mainly composed of a 4-bit resistor-string digital-to-analog converter (RDAC) and a 2-bit voltage divider implemented by stacked diode-connected transistors. The novel soft-start circuit has been designed with a 0. 1 $\mathrm{S}\mu \mathrm{m}$ CMOS process as part of a buck converter and only occupies 0.00483 mm2 on silicon with a supply voltage of 3.3 V.