A voltage mode buck DC-DC converter with automatic PWM/PSM mode switching by detecting the transient inductor current

摘要

This paper presents a voltage mode buck DC-DC converter that integrates pulse-width modulation (PWM) and pulse-skipping modulation (PSM) to achieve high efficiency under heavy and light load conditions, respectively. Automatic mode-switching is implemented simply by detecting the voltage drop of high-side power switch when it is on, which indicates the transient current flowing through the inductor. Unlike other methods based on average current sensing, the proposed auto-mode switching scheme is implemented based on voltage comparison and simple control logic circuit. In order to avoid unstable mode switching near the load condition boundary, the mode switching threshold voltage is set differently in PWM and PSM mode. Besides, a 16-cycle counter is also used to ensure correct detection of the change in the load condition and fast response of the converter. In addition, a dual-path error amplifier with clamp circuit is also adopted to realize loop compensation and ensure 100% duty cycle operation. Fabricated in a 0.18-μm standard CMOS technology, the DC-DC converter is able to operate under supply voltage from 2.8 to 5.5 V with 3-MHz clock frequency. Measurement results show that the converter achieves a peak efficiency of 93%, and an output voltage ripple of less than 40 mV, while the chip area is 1.02 mm~2.