A 97% Peak Efficiency and 308 A/in3 Current Density 48-to-4 V Two-Stage Resonant Switched-Capacitor Converter for Data Center Applications

Abstract

Resonant switched-capacitor (SC) converters have shown great potential in achieving high efficiency and high current/power density, due to their better passives and switch utilization compared to the conventional switched inductor and SC converters. The series-parallel (SP) topology has excellent passive component utilizations, since all flying capacitors sustain the same lowest voltage (i.e. the output voltage) with the minimum voltage derating factors. In this work, a 48 V-to- 4V two-stage hybrid SC converter, cascading a 2-to-1 resonant SC converter (highvoltage stage, using 40 V switches) and a 6-to-1 hybrid series-parallel SC converter (high-current stage, using 25 V switches), is designed, built and tested. The hardware prototype achieves 97% peak system efficiency (including gate driver losses) through the use of zero voltage switching (ZVS) control techniques for both stages. A peak current density of 308 A/in3 or a peak power density of 1154 W/in3 is achieved.