Digital Average Current Programmed Mode Control for Multi-level Flying Capacitor Converters

This paper explores flying capacitor voltage (v(Cfly)) stabilization for multi-level flying capacitor (ML-FC) converters operated in average current programmed mode (CPM) control and demonstrates that the implementation is dependent on output loading condition. The dependency is characterized by the ratio K = I-Boundary/I-Load = 1 as the controller boundary condition between intrinsic and forced stable v(Cfly) dynamics, where L-Boundary, a function of inductor selection and converter operating condition, is the location that active v(Cfly) controller behaves in a positive feedback manner. Consequently, a novel adaptive control strategy is introduced with the ability to seamlessly transition between intrinsic to active v(Cfly) stabilization based on a simple criterion indirectly measuring the ratio K. Finally, the proposed concepts are verified using an experimental setup implementing a three level FC buck converter Point of Load (PoL) regulator converting 12 V to 3.3 V from light to heavy load.