Two-Stage 48-V VRM With Intermediate Bus Voltage Optimization for Data Centers

In this article, a high-efficiency and power-density unregulated inductor-inductor-capacitor (LLC) converter (DCX) is proposed for a first-stage converter in a two-stage 48-V voltage regulator module (VRM) for data center applications. The intermediate bus voltage in the two-stage architecture is evaluated by designing two LLC-DCX converters with fixed transformation ratios of (4:1) and (8:1). The overall efficiency of the two-stage architecture is evaluated, and the optimal bus voltage is selected. The LLC-DCX is designed using gallium nitride (GaN) devices and an optimized integrated magnetic structure. An enhanced primary and secondary termination method, as well as a printed circuit board (PCB) winding structure for equal current sharing among all transformer layers, is proposed, A significant reduction in the total conduction loss for the high-frequency transformer is achieved. The designed LLC-DCX can provide a continuous output power of 900 W with maximum efficiencies of 98.4% for the (4:1) conversion, and 98.0% for the (8:1) conversion, with high-power densities of 1600 and 1200 W/in
³
, respectively. The overall efficiency of the two-stage VRM was evaluated, and the results show a superior performance when using a lower bus voltage of 6 V.