It is not clear in the datasheet how to select the value of the resistor connected from CCM/SYNC0 to ground. The datasheet says “To force the device into FCCM, connect the CCM/SYNCO pin to GND using a 10kΩ to 300kΩ resistor.” What is the difference in the selected value.
Additionally, what is the downside to just running the device in AAM? I guess a variable switching frequency which might impact emissions?
There shouldn’t be any difference for resistor values in the 10k-300k ohm range, any of them should put the IC into FCCM.
FCCM is useful for keeping the output voltage stable with low ripple during light load, however this isn’t very efficient.
AAM is useful for keeping the system efficient during light or no load conditions, however it does create a lot of output ripple and is generally quite noisy.
I hope this was helpful.