The Switching Bus Converter: A High-Performance 48-V-to-1-V Architecture With Increased Switched-Capacitor Conversion Ratio

Abstract

This paper proposes a switching bus converter, an efficient and compact hybrid switched-capacitor (SC) voltage regulator, for direct 48 V to Point-of-Load (PoL) power conversion in data centers. The proposed topology merges a 2-to-1 SC front-end with two 8-branch series-capacitor-buck (SCB) modules through two switching buses. Compared to the existing DC-bus-based architecture, the proposed switching-bus-based architecture does not require DC bus capacitors, reduces the number of switches, and ensures complete soft-charging operation. In addition, this paper conducts a comparative performance analysis of different regulated hybrid SC topologies, which reveals that a larger SC conversion ratio is advantageous for achieving higher performance. Through the two-phase operation of the SCB modules, the proposed topology extends the maximum duty ratio and enables a larger SC conversion ratio. A hardware prototype was designed and built with custom two-phase coupled inductors and synchronous bootstrap daughterboards to validate the theoretical potential of the proposed topology. The hardware prototype was tested up to 500-A output current at 1-V output voltage, achieving 93.4% peak system efficiency, 86.1% full-load system efficiency, and 464-W/in 3 power density. Moreover, the theoretical benefits of a larger SC conversion ratio were experimentally verified with measured performance at different SC conversion ratios.Index Terms-Comparative analysis, coupled inductor, commutation loop, point-of-load (PoL), hybrid switched-capacitor (SC) converter, high conversion ratio, voltage regulation module (VRM), switching-bus-based architecture, synchronous bootstrapping. * Switching frequency of the voltage regulation stage.* * Power density calculated by the box volume. † Gate drive loss is included in the calculation of system efficiency.‡ Recommended and provided by Vicor's online Power System Designer.