On-chip three-phase coupled power inductor for switching power converters

This paper presents an on-chip three-phase coupled power inductor (3-CPI) structure which consists of a layer of ferrite core material and another layer of three phase coupled spiral windings on a silicon substrate. The flux cancellation effect of the inversely coupled windings significantly reduces the net flux in the ferrite layer, which helps increasing the saturation current of the power inductor. An ANSYS®/Maxwell® 3-D physical model of an 8mm×7.6mm 3-CPI design is developed and simulation results are obtained. Simulation results show that the saturation current (12A/phase) of the 3-CPI is twice the saturation current (6A) of the non-coupled power inductor with the same inductance density. Based on a 5V/1.5V 5MHz three-phase buck converter design, the equivalent steady-state inductance and transient inductance of the 3-CPI design are calculated to be equal to 33.8nH and 7.2nH, respectively.