A 48V to 3V-5V Hybrid Converter with Inductor at Low-Q Stage Achieving 93.4% Peak Efficiency and 723W/in3 Power Density for AI Servers

This paper presents a hybrid buck converter with inductor at low-charge stage designed to convert 48V to 3V-5V for powering AI servers. This converter is based on a Fibonacci switched-capacitor topology with an optimized wiring method for fully utilizing flying capacitors to realize a large voltage conversion ratio. Moreover, with an inductor placed at the low-charge stage, inductor current is further reduced, and hence inductor DCR loss is significantly reduced for enhanced efficiency, and the reliance on a bulky inductor is mitigated for better power density. A hardware prototype was implemented with discrete MOSFETs and drivers to validate the proposed converter, providing a maximum output current of 30A. Measurement results show that the converter achieves a peak efficiency of 93.4% and a power density of up to 723W/in³.