A resonant switched-capacitor converter with GaN transistors for series-stacked processors with 99.8% power delivery efficiency

The series-stacked architecture provides a method to increase power delivery efficiency to multiple processors. With a series-stack, Differential Power Processing (DPP) is needed to ensure that processor voltages remain within design limits as the individual loads vary. This work demonstrates a switched-capacitor (SC) converter to balance a stack of four ARM® Cortex-A8 based embedded computers. We investigate hard-switched and resonant modes of operation in a ladder SC DPP converter, implemented with GaN transistors. Excellent 5 V regulation of each embedded computer is demonstrated in a 4-series-stack configuration, with realistic computational work loads. Moreover, we demonstrate hot-swapping of individual computers with maintained voltage regulation at all nodes. A peak stack power delivery of 99.8% is demonstrated, and DPP switching frequencies from 250kHz to 2MHz.