A two-phase buck converter with optimum phase selection for low power applications

A two-phase buck converter with optimum phase selection for low power applications is presented in this paper. The two-phase converter has a baby-buck phase optimized for light load and a heavy-load phase optimized for heavy load. The phase selector selects an appropriate phase depending on the load current to improve the efficiency. The two phases adopt pulse frequency modulation with constant on-time valley current mode control, in which the baby-buck phase operates mostly in discontinuous conduction mode (DCM) to increase light load efficiency while the heavy-load phase in continuous conduction mode (CCM). The load of the proposed converter ranges from 30 mW to 1 W, with efficiency ranging from 64% to 87%, respectfully. The baby-buck phase achieves the maximum efficiency of 81% at the load of 200 mW and the heavy-load phase 88.2% at 750 mW.