Wide Voltage Range High-Efficiency Sigma Converter 48V VRM With Integrated Magnetics

Abstract

In this paper, a high-efficiency and power-density single-stage 48V voltage regulator module (VRM) based on a Sigma converter power architecture is proposed for CPU in data center applications. The proposed converter overcomes the limitation of wide voltage range operation in the Sigma converter architecture by utilizing a variable gain LLC converter by which the voltage distribution among the buck converter and the LLC converter in the quasi-parallel structure is maintained in the ranges that allow the highest possible conversion efficiency. A magnetic integration method is proposed for the variable gain LLC converter by which a PCB winding matrix transformer structure and resonant inductor are integrated with a single core structure and minimum winding requirement to achieve the required gain characteristics. A wide voltage range Sigma converter prototype is built that can operate with input voltage range of (40-60V) and output voltage range of (1.3-1.8V) while providing a maximum output current of 120A, the designed converter can achieve a maximum efficiency of 95.2% and a power-density of 700W/in3.