Butterfly Interleaving Winding Arrangements for Multiphase Coupled Inductors

Multiphase coupled inductors in pulse-width modulated (PWM) converters benefit from the reduced steady-state current ripple and fast transient performance. This article proposes a magnetic core geometry together with a butterfly interleaving winding arrangement to integrate the four-phase negative coupled inductors. It adopts the interleaving winding strategy usually used in planar transformers to reduce the proximity effect. Basically, each winding has two overlapped areas with other two windings. The two currents in the overlapped area are in opposite directions. The proximity effect is, therefore, reduced. Compared with the conventional nonoverlapped winding arrangement, finite element analysis simulation indicates more than 60% ac resistance reduction and almost 30% footprint minimization. Both design considerations and design guidelines for the multiphase buck converter with coupled inductors are presented. The magnetic core and winding structure are demonstrated in a 36–75 V (nominal at 48 V) to 30 V four-phase negative coupled buck converter as a front stage for datacenter applications. It is implemented on a six-layer printed circuit board (PCB) without any parallel winding connections, and can operate up to 1165 W. The experiment shows the prototype achieves 99.3% peak efficiency with 912 W/in3 power density.