A Single-Inductor Multi-Ratio Resonant Ladder dc-dc Converter Achieving > 80% Efficiency over 0.4-to-1.4V Output Voltage Range

This paper introduces a resonant ladder topology that can provide non-unit fraction, N:N-1, resonant voltage conversion ratios while eliminating the charge-sharing loss of all flying capacitors in a converter using a single inductor. Instead of connecting the inductor at the output side, which places the switches between the inductor and capacitors and exposes them to high voltage swings, as in prior non-unit fraction resonant converters, the inductor in the proposed topology is arranged in a series tank configuration. Additionally, the suggested converter requires a two-phase switching sequence instead of a multi-phase one to soft charge all existing flying capacitors. Furthermore, the topology does not change the converter’s resonant frequency among the consecutive switching phases. Importantly, the parent SC topology of the proposed resonant converter is the SC ladder topology that achieves the minimum switch V-A stress applicable to all dc-dc converters for a given conversion ratio. The power FETs in the bottom (N–1) half bridges of the proposed ladder converter are operated as diodes to allow efficient continuous output voltage regulation below the native N:N-1 resonant ratio using frequency or duty modulation. Furthermore, to maintain high efficiency across a wide output voltage range, a recursive reconfiguration structure is introduced that enables altering N and the conversion ratio, N:N-1, offering multiple resonant ratios using a single tank-connected inductor without disconnecting a single capacitor or altering the resonant frequency. Circuit simulation results of a 0.18µm design demonstrate the principal advantages of the proposed recursive resonant converter, where greater than 80% efficiency is achieved, with a 95.6% peak value, over an output range from 0.4 to 1.4V under a load current of 6A.