4C 3-Level Hybrid Buck Converter for 12~48V-to-1V Point-of-Load Applications

Abstract

There is high demand for Point-of-Load (PoL) power converters to have ultra-low voltage conversion ratio (VCR) with wide input voltage range (12 48V) and low output voltage (1V). A conventional half-bridge buck converter with ultra-low VCR suffers severe power loss due to very low duty ratio (D). Power efficiency can be improved by a hybrid converter, which integrates a first stage step-down switched-capacitor converter (SCC) with a second stage buck converter that could have higher effective duty ratio. The SCC steps down the input voltage $\left(V_{\mathrm{IN}}\right)$ to an intermediate voltage level with a fixed VCR, and the duty ratio of the buck converter determines the overall VCR. Prior efforts included the one-capacitor (1C) 3-level (3L) converter [1], the two-capacitor (2C) $3 \mathrm{~L}$ converter [2], and the double step-down (DSD) converter [3]. These $S C C$ s all have $V C R S C C=1 / 2 X$ With VIN as high as $48 \mathrm{~V}$, it is more efficient to use a SCC with lower VCR, such as the hybrid converter of [4] that implemented a Dickson SCC with VCRSCC $=1 / 4 \mathrm{X}$ by stacking four power switches with star configuration. However, for VIN higher than $12 \mathrm{~V}$, it is not trivial to generate floating supply-voltages for the bootstrapped gate-drivers with four levels of power switches. Alternatively, one may combine the SCC of the 1C $3 \mathrm{~L}$ converter with that of the DSD converter to realize a tri-state DSD converter [5], with VCRscc $=1 / 4 \mathrm{X}$. However, this converter must use two power inductors with 4-phase operation.