Vertical Stacked 48V-1V LEGO-PoL CPU Voltage Regulator with 1A/mm² Current Density

This paper presents a 48 V–1 V merged-two-stage hybrid-switched-capacitor voltage regulator with a Linear Extendable Group Operated Point-of-Load (LEGO-PoL) architecture for high-current microprocessors, featuring vertical stacked packaging and coupled inductors. The architecture is highly modular and scalable. The switched-capacitor circuits are connected in series on the input side to split the high input voltage into multiple stacked voltage domains. The multiphase buck circuits are connected in parallel to distribute the high output current into multiple parallel current paths. A 780 A vertical stacked CPU voltage regulator with a peak efficiency of 91.1% and a full load efficiency of 79.2% at 1 V output voltage with liquid cooling is built and tested. This is the first demonstration of a 48 V–1 V CPU voltage regulator achieving over 1 A/mm ² current density and 1,000 W/in ³ power density. The output voltage is regulated between 0.8 V and 1.5 V through the entire 780 A range.