A 94.7% Efficiency Direct-Step-Down Switched-Tank-Based 48V to 1V-3.3V Hybrid Converter with Constant-Resonant-Time Closed-Loop Control

This paper presents a new hybrid topology for 48V to point-of-load DC-DC converters. The proposed direct-step-down switched tank converter (DSDSTC) combines a resonant switched-tank stage and a non-resonant buck stage into a single stage with shared power switches. By adjusting the global duty-cycle between the effective stages, closed-loop regulation is achieved with a comparator-based low-complexity constant-resonant-time (CRT) control with fast transient response. A prototype has been designed using 8 GaN switches (at least 4 less than the original conceptual design presented by Google) for 48V to 1-3.3V conversion, achieving a peak efficiency of 94.7%, a maximum current of 50A and a maximum power density of 595-W/in3. Only a 40-mV droop is observed in a 1-20A load transient.