MSC-PoL: Hybrid GaN-Si Multistacked Switched Capacitor 48V PwrSiP VRM for Chiplets

Abstract

This paper presents a multistack switched-capacitor point-of-load (MSC-PoL) voltage regulation module (VRM) with coupled magnetics for ultrahigh-current chiplet systems. In the MSC-PoL architecture, the stacked switched-capacitor cells split the high input voltage into several intermediate voltage rails, which are loaded with the switched-inductor cells to achieve soft charging and voltage regulation. Automatic capacitor voltage balancing and inductor current sharing are realized during the soft charging process. Many inductors of the switched-inductor cells are coupled into one and operated in interleaving to reduce the inductor current ripple and boost the transient speed. A 48-to-1-V/450-A VRM containing two MSC-PoL modules is built and tested, leveraging high voltage GaN devices for the frontend and high current Silicon devices for the back-end. Two ladder-structured coupled inductor designs are developed and compared, one of which installs a leakage magnetic plate to adjust the leakage inductance for lower current ripple. Featuring 3D stacked packaging, the entire power stage, gate drivers, and bootstrap circuits of one MSC-PoL module are enclosed into a 1/16-brick/0.31-in3/6-mm-thick package. The peak and the fullload efficiencies as well as the full-load power density (including both gate loss and size) of the MSC-PoL prototype with and without using the leakage plate are 91.7% and 89.5%, 85.8% and 85.6%, and 621 W/in3 and 724 W/in3, respectively. The 6-mm-thick MSC-PoL converter can be embedded into the chiplet or CPU socket, enabling power-supply-in-package (PwrSiP) for extreme efficiency, density, and control bandwidth.