Desgin considerations of auto phase number control in multiphase voltage regulators

Automatic phase number control in multiphase voltage regulators can optimize the efficiency over a wide load range by adjusting the operational phase number according to the load current level. Several challenges limit its adoption in real applications. The dropped phases must respond immediately when a step load applies. The compensation network should be adjusted according to the phase number to keep the system stable under all operational conditions. The output voltage ripple and load line, during different phase number operation and during the transitioning of phase adding or dropping, should be kept within the spec. In this paper, some design considerations of auto phase number control are discussed in detail and illustrated with realizations of both optimal efficiency and transient performance across the entire load range.