A Recursive Switched-Capacitor DC-DC Converter Achieving Ratios With High Ef ficiency Over a Wide Output V oltage Range Loai G. Salem , Student Member , IEEE, and Patrick P . Mercier , Member , IEEE

Abstract

A Recursive Switched-Capacitor (RSC) topology is introduced that enables recon figuration among 2 –1 conversion ratios while achieving minimal capacitive charge-sharing loss for a given silicon area. All 2 –1 ratios are realized by strategically interconnecting 2:1 SC cells either in series, in parallel, or in a stacked con figuration such that the number of input and ground connections are maximized in order to minimize cascaded losses. Importantly, all ratios are dynamically recon figurable without disconnecting a single capacitor, all while ensuring optimal capaci- tance/conductance relative-sizing. The RSC topology is inherently regular, enabling recursive inter-cell connection and recursive binary-slicing that implement ratio-recon figuration with min- imum complexity and losses. A sca lable all-digital binary search controller is employed to perform ratio-recon figuration among the available 2 –1 ratios without using any ratio-threshold generation circuitry. To validate the topology, a 4 bit RSC is fully integrated in 0.25 µm bulk CMOS using MIM capacitors, achieving greater than 70% ef ficiency over a 0.8–2.2 V output voltage range with 85.8% peak-ef ficiency from a 2.5V input supply. Compared to a co-fabricated three-ratio (1/3, 1/2, 2/3) Series-Parallel SC con- verter, the RSC achieves a 40.4% larger output operating range (from 0.04 to 2.2 V), and fills the ef ficiency-drops in-between the three-ratios by 8% with a 940 load.