Analysis of Ripple-Suppression and ZVS Operating Boundaries in MHz Interleaved GaN Buck Converters with PCB Air-Core Inverse-Coupled Inductors

Inverse-coupled inductors suppress phase-current ripple in interleaved buck converters, whereas high-side zero-voltage switching (ZVS) requires sufficient negative valley current for switch-node commutation. These opposing requirements create an inherent tradeoff between ripple suppression and ZVS capability. This paper develops a ripple–ZVS operating-boundary framework for a two-phase interleaved GaN buck converter using a PCB air-core inverse-coupled inductor. Ripple and ZVS boundaries are derived for the low- and high-duty regions, with loss sensitivities analyzed in terms of the phase-current trajectory and switching frequency. At 10 MHz, measurements on a 12 V-input prototype show ripple reductions of 4.2% at 3.3 V and 18.5% at 5 V, with corresponding efficiency changes of +3.9 and −1.4 percentage points. The ZVS boundary frequency is approximately 3 MHz for both configurations at 3.3 V, but decreases from 2.8 to 1.5 MHz with inverse coupling at 5 V. Load sweeps show that frequency-reduced ZVS is more efficient at light load, whereas 10 MHz fixed-frequency operation is more efficient at high load. Thus, neither ripple suppression nor ZVS alone determines which operating strategy is more efficient; their operating boundaries and loss tradeoffs must be considered jointly.