Critical bandwidth for the load transient response of voltage regulator modules

This paper investigates the relationship between the control bandwidth and the load transient response in voltage regulator modules (VRMs), which are designed with multiphase interleaving synchronous buck converters. Both voltage- and current-mode controls are discussed. A critical bandwidth value is discovered, beyond which pushing the bandwidth can no longer reduce the output voltage spike during the load transient response. Also, the critical bandwidths are different according to different kinds of output capacitors. The critical bandwidth concept highlights the trend of high-frequency VRM design that uses ceramic capacitors to achieve smaller size and faster load transient response. Simulation and experimental results prove the theoretical analysis.