Autotuning of Resonant Switched-Capacitor Converters for Zero Current Switching and Terminal Capacitance Reduction

As a result of their soft-charging and soft-switching capabilities, resonant switched-capacitor (ReSC) converters can achieve higher efficiencies and power densities than pure switched-capacitor (SC) converters. However, the terminal capacitors (i.e, the input and output capacitors) still consume a large volume in ReSC converters and represent the new bottleneck for converter miniaturization. Theoretically, when the terminal capacitances are reduced, an optimum clocking scheme that preserves multi-resonant operation can be calculated. In practice, this optimal operating point may not be precisely obtained due to circuit parasitics, passive component tolerance and derating. This paper demonstrates a closed-loop hysteretic control method that can dynamically track the zero current switching (ZCS) operating point and allow for a reduction in terminal filtering capacitors via multi-resonant operation. A 48-to-24-V ReSC converter prototype is designed and constructed to verify the effectiveness of the proposed control method. The controller is demonstrated to successfully track the ZCS operating point, enabling over 70% reduction in terminal capacitor volume. In the case of reduced terminal capacitances, the controller achieves up to 44% reduction in power loss compared with the conventional open-loop control without ZCS autotuning.