Switched-Capacitor Based Buck Converter Design Using Current Limiter for Better Efficiency and Output Ripple

Abstract

In this paper we are addressing power efficiency and output ripple of an embedded switched-capacitor based DC/DC Buck Converters. Here we propose to use current pump based switched-capacitor circuit in buck converter. The current pump circuit limits transition current of the switched-capacitors and hence, improves power efficiency and reduces output ripple. We have also proposed an equivalent macro model of this type of current pump based switched-capacitor converter which would help to get a better essence of the closed loop stability of the system and would reveal clearly trade-offs among load current,  flying capacitance and clock frequency. A transistor level implementation of the proposed buck converter in 0.18µ technology is provided. For a load current of 8mA (maximum)the achieved power efficiency is 72.7% and the output ripple is 27mV. The flying capacitors in the converter are 2x108pF and the load capacitor is 125pF.