Small-Signal Circuit Model for Synchronous Buck DC/DC Converter featuring ZVS at Low-Side

In this paper we provide an improved small-signal equivalent circuit model of a synchronous Buck converter which operates in Continuous Conduction Mode (CCM) and includes an alternative Zero Voltage Switching (ZVS) mechanism for the low-side power MOSFET that rely on the MOSFETs output capacitance. The addressed analysis improves the state of the art in DC/DC small-signal modeling as it is capable to predict unexpected effects on the dynamical system response such as the dependency on input voltage introduced by parasitics. Therefore, a complete design tool which permits to evaluate the impact of the MOSFETs output capacitance and the ZVS network on the converter dynamics is proposed. The derived equivalent circuit model which includes an additional feedforward path and a feedback loop is analyzed and the main open-loop transfer functions (control-to-output, line-to-output, output impedance) are analytically assessed. A verification has been carried out through SIMPLIS circuital simulations, corroborating the validity of the whole evaluation process.