Design Procedure for Reduced Filter Size in a Buck Converter Using a Fourth-Order Resonance Filter

This article presents a novel design procedure for fourth order and fourth-order resonance (4thRes) output filters, for given buck converter specifications, making components selection a straightforward process. An accurate filter analysis is provided to predict the filter component currents and voltages in both frequency and time domains. Application of the analysis in a design study of a 20 MHz, 5.4 W buck converter shows that the 4thRes filter has the potential to reduce the output passive components for a wide duty cycle range. As compared with a second-order filter at VIN = 6.6 V to VOUT = 1.8 V, total inductance, inductor energy, capacitance, and capacitor energy are 58%, 35%, 45%, and 31% lower, respectively. Air-core printed circuit board (PCB) integrated solenoid inductors are considered for implementation and testing within a prototype converter to show the impact of these filters on the converter performance. The 4thRes filter achieved 3.7% and 3.6% higher full-load efficiency than the second- and fourth-order filters, respectively, and a better load transient performance.