IC Design for Pseudo-Continuous Conduction Buck Converter with Dynamic Freewheeling Control

Abstract

The buck converter operating in pseudo- continuous conduction mode (PCCM) increases the ability of current handling compared with discontinuous conduction mode (DCM). Same as DCM operation, the control-to-output transfer function of PCCM buck converter exhibits a single pole, which make the transient response faster than that of CCM operation. The most commonly used control for PCCM buck is constant reference current (CRC) control, which needs sensing device to determine the freewheeling time. CRC control suffers from low efficiency under light load condition because of long freewheeling time. The dynamic freewheeling-time (DFT) control for PCCM buck converter is proposed to solve the issue mentioned above. The proposed DFT control uses feedback signal to determine the freewheeling time, which make the freewheeling time vary with load condition at transient state. Thus, the sensing device is needless in DFT control. The proposed DFT control decreases the freewheeling current value under the light load condition. Furthermore, the proposed DFT control can operate in DCM at very light load condition and the freewheeling current is zero. Thus, the light load efficiency of buck converter can be improved. Finally, TSMC 0.25 pm high voltage process is used to implement the proposed control circuit, and applied to an input voltage of 12 V, output voltage of 3.3 V, and output power of 6.6 W buck converter to verify the feasibility of proposed control IC.