This circuit uses a current mode controller with an oscillation frequency response of:
In the circuit, the designer chose to use a 10nF cap, with a 680 ohm timing resistor, which according to the datasheet, is the absolute minimum resistance that should be used in the timing circuit, as shown below:
The output frequency of this yields the MOSFET being pulsed at around 147 kHz. I was wondering if there was a reason these components were chosen in this case. I had a hunch it was because of the coupled inductors being used in this case, but I don't know where to begin on finding the best frequency to oscillate that at. And if that was the case, why not use different values to get to that 150kHz, such as a 2.4K resistor and a 5nF capacitor? Any insight is welcome on this.