Dynamic Effects of Mismatched Time Constants in DC-DC Converters with Inductor DCR Current Sensing

This paper analyzes the effects of time constant mismatch on the dynamic behavior of current-controlled DC-DC converters that employ the lossless DCR inductor current sensing technique. Modeling of such mismatch is often oversimplified in the literature and treated as a simple modification of the small-signal modulator gain. The analysis proposed in this paper, on the contrary, demonstrates that time constant mismatch also affects the current loop gain in the low frequency region. Furthermore, the analysis indicates that the mismatch can even be intentionally exploited so as to achieve specific advantages in current-controlled DC-DC converters. Modified small-signal models for both peak and average current-mode control techniques are proposed and discussed, and a two-phase synchronous Buck converter for battery charger applications is considered to experimentally validate the theoretical analysis.