Design considerations for VRM transient response based on the output impedance

This paper discusses the transient response of voltage regulator modules (VRMs) based on the small-signal models. The concept of constant resistive output impedance design for the VRM is proposed, and its limitations in applications are analyzed. The impacts of the output filter and the feedback control bandwidth show that there is an optimal design that allows the VRM to achieve fast transient response, small size and good efficiency. Simulations and experimental results prove the theoretical analysis.