A Reconfigurable Dual-Output Switched-Capacitor DC-DC Regulator With Sub-Harmonic Adaptive-On-Time Control for Low-Power Applications Zhe Hua , Student Member , IEEE,a n dH o i L e e, Senior Member , IEEE

Abstract

This paper presents a reconfigurable switched-ca- pacitor (SC) DC-DC regulator to simultaneously generate two different regulated output voltages for low-power applications. With capacitor and power switch sharing in the power stage, the area efficiency of the propo sed regulator is improved. The proposed power stage can also be configured to provide different conversion ratios in order to maintain high power efficiency of the regulator in different input voltages. A sub-harmonic adap- tive-on-time (SHAOT) control sc heme is developed to regulate both outputs. The adaptive-on-time control automatically adjusts the durations of charge transfer to both outputs to reduce output voltage ripples under different input voltages. Switching power transistors at the fundamental or sub-harmonics of the system clock frequency can provide predictable noise spectrum to both regulated outputs and improve the light-load regulator power efficiency. The cross regulation between both outputs can also be minimized by the proposed SHAOT scheme. Implemented in a standard 0.35 µm CMOS process, the proposed regulator provides two regulated outputs of 2 V and 3 V and delivers up to 12 mA at each output. The proposed regu lator achieves a maximum power efficiency of 89.5%. Both power ef ficiency and output ripple can be improved by 10% and 4 times, respectively, over a wide input range from 1.1 V to 1.8 V by using the proposed reconfigurable power stage and adaptive-on-time scheme.