A Regulated Cascaded Hybrid Switched-Capacitor Converter with Soft-Charging and Zero Voltage Switching for 48-to-12-V Applications

The cascaded resonant switched-capacitor converter is an energy-efficient and power-dense solution to unregulated 48-to-12-V power conversion. This work explores approaches to achieve output voltage regulation with this topology while maintaining high efficiency and high power density. The two switch nodes at the second stage are merged into one for the automatic balancing of capacitor voltages. A hybrid resonant-PWM control method is presented to realize soft charging of the middle capacitor and flying capacitors. At 12-V fixed output voltage, it achieves a power density of 3115 $\mathrm{W}/\text{in}^{3}$, a peak efficiency of 99.0% with 48-V input and 98.6% with 54-V input (including gate drive loss), both of which are among the best in the state-of-the-art regulated 48-to-12-V solutions.

I. Introduction

Intermediate bus converters (IBC) are widely used in 48-V power distribution systems such as data centers, communication base stations, and electric vehicles. To power low-voltage devices in the system (e.g., CPU, GPU, and memory), a two-stage architecture is usually adopted, including an unregulated 48-to-12-V IBC as the first stage and a multi-phase buck converter as the second stage [1]. Note that there are also 12-V loads in the system (e.g., CPU fan, hard disk drive, automotive battery, etc.), which require the IBC to provide a regulated 12 V voltage. In this paper, a cascaded hybrid switched-capacitor (SC) converter is presented for regulated 48-to-12-V conversion with improved power density and efficiency.