An improved PFM control scheme for Three-Level Buck Converter based on Ton Extension Achieving an 810% Frequency Reduction

This work introduced a novel controlling technique of Pulse Width Modulation (PFM) on a three-level buck converter, to keep remarkable efficiency within wide range of duty cycle and loading. Since this interleaved signal converter with conventional constant on-time control cannot scale their switching frequency with load under discontinuous conduction mode when the conversion ratio(M) is larger than 0.5, an on-time extension method is applied. Additionally, a V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LX</inf> sensing scheme is proposed to achieve flying capacitor balancing in both CCM and DCM throughout the entire duty cycle. The chip prototype is designed using a TSMC 0.18um CMOS process. The simulation results show a 2MHz switching frequency with and a loading range from 20mA to 1A with > 90% efficiency.