A Current-Density-Enhanced 12V-to-1.2V/10A, AOT-Controlled, 4-Phase Series-Capacitor Buck Converter with Embedded Current Balancing

Abstract

This paper presents a 4-phase series-capacitor buck converter (SCB) for high step-down-ratio, high-current point-of-load applications. A current-balancing strategy embedded in the adaptive-on-time controller is proposed to effectively address the inductor current mismatch between different phases. This significantly reduces the required size of the external inductor and thus the converter volume. The proposed current balancing scheme also saves 2 current sensors compared to that of the traditional 4-phase interleaved buck converters. Implemented in a 0.35µm CMOS technology, the proposed 4-phase SCB converter with e-mode GaN FETs supports the full load of 10A and achieves the peak power efficiency of 92.5% under 12V-to-1.2V conversion and 2.5MHz/phase operation. The load current is verified to be equally distributed among 4 phases in both steady-state and transient conditions. Compared to state-of-the-art converters from industry and literature, the proposed 4-phase SCB converter simultaneously achieves the highest power efficiency and the largest current density.