A 48-V-to-1-V Switching Bus Converter for Ultra-High-Current Applications

Abstract

This paper presents an ultra-high-current switching bus converter with direct 48-V-to-1-V power conversion for next-generation ultra-high-power digital loads (e.g., CPUs, GPUs, ASICs, etc.). In the proposed topology, two 2-to-1 switched-capacitor (SC) front-ends are merged with four 10-branch series-capacitor buck (SCB) modules through two switching buses. Compared to the DC-bus-based architecture, the switching-bus-based architecture does not require DC bus capacitors, reduces the number of switches, and ensures complete soft-charging operation. Through two-phase operation within each SCB module, the switching bus converter extends the maximum duty ratio and achieves a very large SC stage conversion ratio of 20-to-1. Compared to existing 48-V-to-1-V hybrid SC demonstrations, the proposed topology has the lowest normalized switch stress and the smallest normalized passive component volume, showing great potential for both higher efficiency and higher power density than prior solutions. A 48-V-to-1-V hardware prototype was designed and built with custom four-phase coupled inductors and gate drive daughterboards. Hybrid gate drive circuitry comprising gate-driven charge pump circuits and cascaded bootstrap circuits was customized for the high-side switches in the SCB modules to overcome the challenge of accumulative voltage drops in the conventional cascaded bootstrap circuit. The hardware prototype was tested up to 1200-A output current and achieved 92.4% peak system efficiency, 87.5% full-load efficiency (including gate drive loss), and 607 W/in3 power density (by box volume).