Selection of the Stable Range of the Equivalent Series Resistance (ESR) of the Output Capacitor for a SCALDO Regulator

The Supercapacitor-assisted low-dropout (SCALDO) regulator is a novel technique which enables an LDO regulator to operate close to its minimum input voltage when the headroom voltage is high using a supercapacitor as a lossless voltage dropper. This method maximizes the end-to-end efficiency of the overall circuit while maintaining the useful benefits of a linear regulator design such as the low output noise, the less electromagnetic interference (EMI) and radio-frequency interference (RFI) issues, and the fast dynamic response. The theoretical and experimental foundation of the SCALDO technique has been well established in the past eight years. A fundamental study of the small-signal model of the SCALDO regulator has been conducted based on the low-frequency supercapacitor circulation network. This small-signal analysis is further extended to investigate the stable range of the equivalent series resistance (ESR) of the output capacitor in this paper.