I've noticed that the LTM4691 SPICE model sometimes runs at 1/2 switching frequency, higher than normal output ripple, and subharmonics at 1/8 the switching frequency. This usually happens when the output current exceeds 1A (the LTM4691 is rated to 2A).
In the attached source file, channel 1 (v1p8) shows shows such a behavior4691_ripple.asc.
I wonder if it is the simulation issue or the actual part behaves like this?
Thanks for you input to this