Small-signal analysis of S-hybrid step-down DC-DC converter

As desired in mobile applications, S-Hybrid converter that merges switched-inductor and switched-capacitor operations can significantly relieve on-board thermal issues by distributing heat loss over an input cable and allowing zero onboard inductor. In this architecture, the input cable is used as inductor for power conversion. This paper presents detailed smallsignal analysis of S-Hybrid converter that considers non-idealities of circuit components including equivalent series resistance (ESR) of the cable, on-state resistance of semiconductor switches, and ESR of capacitors. State-space averaging is utilized to fully describe and analyze impacts of each parasitic component on the converter dynamics. Simplified transfer functions to provide controller design insight are derived and verified in comparison with full modeling and simulation. A controller for a 15W prototype converter is designed to verify the analyses and demonstrate improved transient response.