A Wide Conversion Ratio Three-Level DC-DC Converter With Loop-Free Self-Balancing Technique of Flying Capacitor

This paper proposes a loop-free self-balancing technique of flying capacitor for three-level buck converter. The pro-posed converter utilizes two balancing switches in self-balancing circuit, which can adaptively change the series and parallel structure of flying capacitors at different working phases. In two operating modes of duty cycle less than 0.5 and greater than 0.5, the converter can stabilize the flying capacitor voltages at
$V_{IN}\mathbf{/2}$
without any balancing feedback calibration loops. This three-level converter prototype is designed in
$\mathbf{0.18\mu \mathrm{m}}$
BCD process. When input voltage is set to 6V, the converter can provide a 0.4-5.6V wide output voltage range and automatically calibrate flying capacitor voltage to 3V under different conversion ratios and load currents. Simulation results show that the maximum output voltage ripple and inductor current ripple are 2.5mV and 174mA respectively when conversion ratio is equal to 0.25 or 0.75.