We have a LTC3115-2 that has a nominal 28V input and a nominal 28V output. It should be noted that we are trying to power the converter into a 750uF output capacitance (the 9ms soft start time is nowhere near enough). For a while, we saw no issue with this. Here are some waveforms:
Here the green is the current on the output of the converter but before the 750uF capacitance. The blue is the output voltage. You can see that the voltage does reach the target 28V, but there is hiccupping on start up due to some protection.
Here the yellow is the output voltage (no current measured this time). You can see there are 3 hiccups to reach steady state this time.
At first we thought the hiccups were coming from the overcurrent limit, and it was simply retrying, and would do so indefinitely, or (in our case) until the output voltage was reached. This was originally in the sub 50ms time frame. We noticed however, at lower voltages and colder temperatures, it would actually take much much longer (like hundreds of milliseconds). Why would this be the case? What protection are we actually seeing here?
Added a small clarification on how much "longer" was
[edited by: Nino at 10:06 PM (GMT -5) on 3 Dec 2020]