The half-bridge resonant converter is controlled by the nearly 50% duty-cycle variable frequency square-wave voltage. This allows the half bridge to be easily driven by the gate-driver transformer. Compared with a half-bridge driver device, a gate-driver transformer provides a simple and reliable solution, which:

• Eliminates the need for gate driver power supply
• Enables simplified layout
• Prevents shoot-through due to the transformer coupling
• Requires no latch up

The UCC25600 integrates two-gate drivers with 0.4-A source and 0.8-A sink capability to directly drive the gate-driver transformer.

For the LLC resonant converter, it is critical for the gate-driver signal to be precisely symmetrical. Otherwise, the resonant tank operation will be symmetrical. The load current distribution will be unbalanced for the output rectifiers, which in turn require the over-design of the power stages and thermal management.

In UCC25600, the gate-driver output is precisely trimmed to have less than 50-ns mismatch. Although the gate-driver signal is quite symmetrical, it is still recommended to insert the dc blocking capacitor in the gate-driver transformer primary side to prevent transformer saturation during fast transients.