Bootstrap capacitorless DCM VOT buck converter with dead-time-based off-time calibration for magnetic resonance wireless power transfer

This study reports a miniaturised discontinuous conduction mode (DCM) variable on-time (VOT) buck converter providing an output of 1.8 V in the input range of 3-12 V to support applications with large wireless coupling. Conventionally, an additional large capacitor has been used as a bootstrap capacitor to drive the high-side switch of buck converters, which prevents minimisation. In this study, a standalone momentary power consumption level shifter is proposed to remove the additional bootstrap capacitor and increase the power conversion efficiency (PCE) in the buck converter. A Zener diode is utilised to reduce the power consumption of the level shifter. In addition, a dead-time-based off-time calibration circuit is proposed to further increase the PCE by reducing the low-side conduction loss. The proposed circuit is fabricated with a TSMC 0.18-mu m BCD process, and the core circuit occupies an active area of 0.68 mm(2) with two external components. It provides output currents in the range of 20 mu A to 3 mA with a maximum switching frequency of 750 kHz. The maximum efficiency of the converter below 5 mW is 80.2%