Flying Capacitor Voltage Programed Mode Control for Switched-Capacitor Converters

Abstract

This article introduces a control method for switched-capacitor (SC) converters used directly or indirectly in emerging point-of-load (PoL) applications. Compared to conventional methods of controlling SC converters relying on the simple transformer model, the introduced method takes into account system dynamics and improves transient response by effectively reducing the order of the system. This is achieved by controlling the flying capacitor voltage, eliminating its dynamics. The improvement in transient response results in lower output voltage deviation than conventional methods, allowing a reduction in the size of the output capacitor. In addition, this improvement in transient response allows for the elimination of low drop out regulators (LDOs) in some cascaded PoL systems. It has been shown that the inner loop controlling the flying capacitor can be implemented explicitly controlling the top and bottom bounds of the flying capacitor voltage. The advantages of the control method have been demonstrated with mixed-signal experimental results for a 1-W cascaded 4:1 SC converter and a 200-mW 2:1 SC converter and comparative simulations. Advantages compared with output voltage observation only have been verified, varying from a 50% reduction in output voltage deviation in the worst case to no voltage deviation in the best case.