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 V-IN = 6.6 V to V-OUT = 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.

Automated summary

This article presents a new design procedure for fourth order and fourth-order resonance (4thRes) output filters, making component selection a straightforward process for given buck converter specifications. 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 V-IN = 6.6 V to V-OUT = 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.