SAR-ADC 기반의 Power MOSFET 사이즈 자동 선택을 통한 DC-DC 벅 컨버터의 저부하 효율개선

In this paper, we propose a method of improving the light-load efficiency of DC-DC converter using LDO, 4bit SAR-ADC (successive approximation ADC) and power MOSFET size scaling technique. The proposed circuit selects power MOSFET sizes depending on load current and improves the light-load efficiency of the DC-DC converter. For this, we selects the power MOSFET size with the crossing points by the switching loss and the conduction loss. Also, when operating in standby mode or sleep mode, a LDO mode is selected for improving the efficiency. The proposed circuit used four Power MOSFET(X1, X2, X4, X8), and the efficiency is higher than using single MOSFET about the maximum of 30% at light-load. Input voltage is 5V, output voltage is 3.3V and maximum load currents is 500mA.