A Novel PWM/PFM Control Technique for Transient Improvement and High Efficiency Over a Wide Load Range in Buck DC-DC Converter

This paper presents a novel pulse width modulation (PWM) and pulse frequency modulation (PFM) control technique to improve the transient response when the converter transition from PFM mode to PWM mode and improve efficiency over a wide load range. The proposed PWM/PFM control technique used multiplexers combines PWM modulator and PFM modulator together to simplify the circuit. There are two parallel paths to realize the transition from PFM mode to PWM mode for improving transient response. The first path dominates mode transition when the load current changes from light to 120mA-260mA, the second path dominates mode transition when the load current changes from light to 260mA-1A. Simulation results demonstrate that the proposed PWM/PFM control technique can realize auto-mode transition between PWM mode and PFM mode. The undershoot voltage is 75.8mV and recovery time is 3.3μs when the load current changes instantaneously from 10mA to 1A. Meanwhile, above 80% conversion efficiency can be reached over a load current range of 10mA-1A.