Hi treez,

As stated in the datasheet, the best frequency for a device is a compromise between conduction and switching losses.

Smaller size InnoSwitch parts (with smaller last digit) have smaller FET die sizes with larger on state resistance, but smaller output capacitance.

So, for the same frequency they have smaller switching losses than the larger size parts. But for the same rms device current they have larger conduction losses than the higher numbered parts.

So, when optimizing device losses while keeping within limits of practical transformer size, it makes sense to run the smaller device sizes with their smaller output capacitance at higher frequencies.

PowiGaN devices use a different technology for the MOSFET and have significantly lower on state resistance compared to the silicon devices, so they can take larger rms currents and you can minimize total device loss by running them at lower frequencies.

Finally, INN364x devices are designed to run at high input voltages, which results in large capacitive switching loss. To minimize it, it is recommended to run them at lower frequencies.

The specific recommended frequencies were derived by building, testing and optimizing many power supplies using InnoSwitch. The evaluation reports for some of these designs are public available here: https://www.power.com/products/innoswitch/innoswitch3-ep#product_resources