A multimode, switching-surface controlled dc-dc converter with improved light-load efficiency

This paper describes a switching-surface (SS) controlled dc-dc converter that operates in PFM (pulse-frequency modulation) mode. SS control in continuous-current mode (CCM) has, as an essential property, fast response to load transient. To realize the SS control, a simple circuit that generates a switching function by using only one operational amplifier is proposed. In addition to the CCM operation, PFM mode operation is implemented to enhance efficiency at light load. The proposed converter seamlessly switches between CCM and PFM modes depending on load current. Experimental results for a 1 A, 5 to 1.2 V buck converter are shown. The response to a load transient is nearly optimal, limited by only the power-stage components. By using the proposed PFM mode, efficiency is improved by 30% at an output of 10 mA.