Single Mode Near Minimum Deviation Controller for Multi-Level Flying Capacitor Converters

摘要

This paper introduces a constant frequency mixed-signal single mode controller for multi-level dc-dc flying capacitor (ML-FC) converters that practically achieves minimum output voltage deviation transient response and, at the same time, maintains the stability of flying capacitor (FC) voltage. The output voltage loop of the controller is a simple modification of a conventional voltage-mode pulse-width modulated controller, where the polarity change of the output capacitor current is used to synchronize operation of two modified pulse width modulators. During load transients the controller achieves one cycle recovery of the inductor current, with near minimum output voltage deviation and without mode toggling occurring in many other fast recovery methods. To avoid runaway effect and stabilize the FC voltage, two methods, based on modification of the duty ratio and the capacitor current zero-crossing points, are introduced. Controllers effectiveness is verified with a 15 W, 12 V to 3.3 V, three-level FC buck prototype operating at 400 kHz switching frequency (800 kHz ripple frequency).