An auto-reconfigurable dual-output SC DC-DC regulator with sub-harmonic fixed on-time control for energy-harvesting applications

This paper presents an auto-reconfigurable switched-capacitor (SC) DC-DC regulator that is able to simultaneously produce two different regulated output voltages for energy harvesting applications. With capacitor and power switch sharing, the proposed power stage can realize separate 2x and 3x outputs, while saving 1 flying capacitor and 3 power switches compared with using two independent single-output doubler and tripler. The proposed power stage can also self-configure its own conversion ratio according to different input voltages in order to maintain high power efficiency of the regulator. A sub-harmonic fixed on-time control scheme is developed not only to regulate both outputs, but also to improve the light-load regulator power efficiency, minimize the cross-regulation between two outputs, and provide predictable noise spectrum of both regulated outputs. Implemented in a standard 0.35μm CMOS process, the proposed regulator can provide two regulated outputs of ~2V and ~3V under different input voltages from 1.1V to 1.8V, and deliver up to 15mA in each output. The proposed regulator also achieves a maximum power efficiency of 88% and its efficiency is improved by as much as 13% by auto-configuring its power stage from 2x, 3x to 2x, 2x when the input voltage changes from 1.1V to 1.6V.