Design concepts and guidelines for VRMs from a power stage perspective

The VRM design involves meeting many requirements that oppose each other. A fast dynamic response of the VRM is of major importance to reduce the size and cost of the output capacitance. Meanwhile, the efficiency of the converter should be very high to meet specifications. This paper analyzes how this solution can be found, assuming no limitations in the control performance. The key design parameters will be highlighted (low inductance, output capacitance technology, multiphase converters) and design guidelines will be provided. A procedure to determine approximately the maximum number of phases that can make sense for a particular specification is derived.