TIDUET3 Design guide

TIDUET3 February 2021

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2.4.2.6 Switching Frequency

The wide switching frequency of the UCC256403 is from 35 kHz to 1 MHz, which makes this reference design more flexible. To ensure that the temperature rise of the LLC stage is not too high, reduce the loss of the transformer, inductor, and power MOS. The resonant frequency is chosen to be 100 kHz for the consideration of magnetic loss and switching loss.

Equation 28.

Equation 29.

Equation 30.

Equation 31.

After the preliminary parameters are selected, find the closest actual component value that is available, recheck the gain curve with the selected parameters, and then run the time domain simulation to verify the circuit operation. This results in the following resonant tank parameters:

Equation 32.

Equation 33.

Equation 34.

Based on the final resonant tank parameters, the resonant frequency can be calculated as follows:

Equation 35.