48V-to-0.9V Regulator with Fractional Turn Transformer and Enhanced Coupling Inductor

Single-stage 4 8 V-to- 0. 9 V regulated solutions for high-performance processors become increasingly popular. With the increase in DC bus voltage, the decrease in processor operating voltage, and the rise in load variation frequency, high-performance DC-DC converters with higher step-down ratios and higher loop bandwidths are in demand. This paper proposes a buck converter based on fractional turn structure and enhanced coupled inductors. The transformer achieves a higher step-down ratio using a lower number of printed circuit board (PCB) layers through series flux splitting. The secondary side employs a half-turn winding structure to reduce resistance and leakage inductance. By optimizing the layout of synchronous rectifier switches, high-current windings, and terminals, the loop configuration is optimized to minimize losses caused by parasitic inductance. A trans-inductor structure is designed based on the topology to reduce transient output inductance, and the operation mechanisms of the enhanced multiphase coupled inductor is explained. Using standard planar EI cores, a prototype operating at 500 kHz switching frequency with 48 V to 0.9 V conversion, 50 A per phase, achieves a peak efficiency of 90.3% and a current density of 0.2 A / mm². This provides new ideas for future solutions in data centers.