Design Principles of a Symmetrically Coupled Inductor Structure for Multiphase Synchronous Buck Converters

The multiphase interleaved synchronous buck converters with coupled phase inductors are being preferred for voltage regulator modules requiring low output voltage, high output current, and fast transient response since they simultaneously offer better steady-state efficiency and faster dynamic response. In this paper, a novel magnetic core structure for symmetrical coupling of multiphase buck converter phase inductors is proposed, which overcomes several limitations of asymmetrical inductor coupling proposed so far. A new analytical technique to arrive at simple dynamic equivalent circuits of the converter, as well as design guidelines for the proposed inductor structure, is presented. Experimental results from a prototype four-phase synchronous buck converter with the proposed inductor demonstrate 2% to 6% improvement in the converter efficiency compared to a similarly rated converter with uncoupled inductors while retaining the same transient performance.