Magnetic Integration Into a Silicon Carbide Power Module for Current Balancing

Threshold-voltage mismatch among paralleled dies leads to unbalanced turn-on peak currents and switching energies, thus degrading reliability. A passive method employing inversely coupled inductors of tens of nH and drive-source resistors reduces current unbalance. An integrated design of the coupled inductors is required to facilitate their practical use in a power module. A layout to achieve inverse coupling, high coupling coefficient, and low voltage stress, magnetic materials suitable for operation at tens of MHz, and high current rating of tens of amperes with small magnetic core are challenging for its implementation. A module with integrated coupled inductors that achieve inverse coupling by utilizing the copper trace of the substrate and bond wires, size comparable to the silicon carbide die, coupling coefficient higher than 0.98, tens of nH operating at tens of MHz, and current rating of tens of amperes was designed, fabricated, and validated in this work. The coupled inductors with magnetic material of low-temperature cofired ceramics are compatible with existing packaging technology for module fabrication. Effectiveness on reducing transient-current mismatch at various input voltages, load currents, and gate resistances was verified by experiments. Compared with the baseline module resembling commercial modules, the module with integrated coupled inductors reduces current unbalance from 36% to 6.4% and turn-on energy difference from 28% to 2.6% while maintaining the same total switching energy and negligible change of voltage stress.