A 96.6%-Efficiency Inductively Assisted Switched- Capacitor DC-DC Converter with 0.5-to-1.5V Output Voltage Range

Abstract

Power management integrated circuits are essential components in modern computing systems that play a critical role in defining the overall system efficiency and size. Switched-capacitor (SC) converters have emerged as a prime candidate for high-power-density voltage conversion due, in part, to the inherently higher energy density of capacitors as compared to inductors [1]. Unfortunately, SC converters are only efficient at a few discrete input-to-output voltage conversion ratios $\left(n=V_{O U T} / V_{I N}\right)$, which limit efficient dynamic voltage scaling (DVS) operation to small supply voltage ranges. To address this challenge, inductively assisted SC (L-SC) converters employ a small inductor, connected to the input or the ground side, to enable continuous voltage conversion above or below the native SC converter discrete ratio (Fig. 1, top) [2]. Unlike buck and multi-level converters [3], the employed inductor in L-SC converters delivers only a fraction, n for $n\gt0.5$ or $(1-n)$ for $n\lt0.5$, of the load current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LOAD</inf> ) rather than its entire value, where L is placed at the input or ground instead of the output, whereas the embedded SC supplies the remaining amount. In other words, the inductor average current (IL) is proportional to the magnitude of the voltage deviation from the SC discrete ratio, which reduces the L-SC conduction loss than the other two converters. Unfortunately, L-SC converters with an input or ground side inductor provide continuous voltage conversion only above or below the original SC discrete ratio, respectively. The limited voltage conversion range does not suit the needs of modern SoCs, which typically require a $0.5 \mathrm{~V}$-to-1.5V DVS range from a $1.8 \mathrm{~V}$ input voltage $(n=0.28-0.83)$. In order to generate conversion ratios above and below 0.5 using an L-SC converter, two inductors, placed at the input and ground side, are required (Fig. 1, top), almost doubling the size and cost of the converter.