Effects of Stray Inductance on Hard-Switched Switched Capacitor Converters

Switched capacitor (SC) converters are becoming quite popular for use in dc-dc power conversion. The concept of equivalent resistance in SC converters is frequently used to determine conduction losses that occur as a result of the load current. A variety of methodologies have been presented to predict the equivalent resistance in hard-switched SC converters. These works, however, did not consider the effect of stray inductance on equivalent resistance. Current power converter design practices favor higher switching frequencies, moving hard-switched SC converters into operating areas in which stray inductance affects converter performance. This paper presents an analytic equation that can be used to evaluate the effects of stray inductance on the equivalent resistance of SC converters. The concepts proposed here were verified by both digital simulation and a prototype converter. The equations presented can be used to evaluate the effects of stray inductance on SC converter performance, thereby helping designers set a maximum operating frequency to limit those effects.