Mini-LEGO CPU Voltage Regulator

This article presents the design and optimization of aminiaturized 48-V-to-1-V, 240-A linear-extendable group operatedpoint-of-load (LEGO-PoL) CPU voltage regulator module(VRM)-Mini-LEGO-with a volume of 30 mmx11.2 mmx8.4 mm. The Mini-LEGO converter provides vertical power delivery, and it achieves a peak efficiency of 87.1%, a full loadefficiency of 84.1%, and a power density of 1390 W/in 3 when stepping down a 48 V input voltage to an output voltage of 1 V.The Mini-LEGO offers compact device implementation, simplegate drive circuitry, and a fast regulation-stage switching frequency of 1.5 MHz. The 9-mm-by-9-mm, 4-phase, 20-A-per-phase vertical coupled inductor has a per-phase transient inductance of 10.3 nH,with its coupling reducing the ripple by a factor of six, and a heightof 2.5 mm. This vertical coupled inductor structure is designed following a systematic approach to minimizing its height while achieving significant current ripple reduction and maintaining sufficient saturation margin. Thermal simulations are performedto verify the cooling feasibility. A measurement characterization method for vertical coupled inductor structures is introduced andused to characterize the designed vertical coupled inductor