Design and Implementation of a GaN-Based Soft-Switched Series-Capacitor Buck Converter Operating at the CCM-DCM Boundary for High-Performance Computing Systems

This paper presents a novel voltage regulator module (VRM) with zero-voltage switching (ZVS) operation, employing a multiphase-interleaved synchronous series-capacitor buck (SCB) converter operating at the boundary between discontinuous (DCM) and continuous (CCM) conduction modes. Building on our prior work introducing the SCB concept with low-valued filter inductances at this boundary mode and its integration into substrates and processor packages, this study provides a comprehensive circuit-level analysis, including mathematical modeling, operating modes, and ZVS soft-switching mechanism. A GaN-based 12V-to-1V prototype, operating at 0.5 MHz and 200W full load with scalable 3-phase SCB converters, is tested to validate the analysis. ZVS operation, coupled with low-inductance air-core inductors, eliminates core and switching losses. As a result, conduction losses dominate, necessitating low-voltage, low-resistance GaN switches for high efficiency in future designs. The converter's ZVS operation enables megahertz switching frequencies while maintaining low losses and improving power density in future implementations.