You are pretty close but more info is needed to track down the cause - posting soft start waveforms will tell if it works properly up until some other control takes over...
Could you tell me what is the most useful waveforms to look at? I have a 2 channel scope with single reference so I can only look at 2 signals simultaneously with the same reference.
Update - Linear Tech support has finally responded to me in regard to questions on their LTC4020 datasheet (after 2 weeks) and included their proprietary design spreadsheet for the LTC4020. It's password protected so I cannot see how they calculate their values however.
I've updated it with all my specifications and their suggested choke is 0.6uH also, however that results in huge inductor currents (50A Ipeak).
If I put 5.6uH into the spreadsheet, it shows the IL choke current range from 18.5A (at Vin=22V) to 15.7A (at Vin=26V). My RsenseA/B sense resistors are 3mR for 16.6A Iavg limit.
I guess I need to increase the Iavg limit?
It brings me back to these equations from the datasheet:
Using 12A output (same as spreadsheet), I do not get the same values the spreadsheet gets at Vin=22V
IL ~ 12A * (29.2/22)
...
IL ~ 15.9A So where does the 18.3A come from? Safety factor?
The spreadsheet also says Ipeak with a 5.6uH choke is 23.5 A (at Vin=22V)
My choke (for right now) is 5.6uH, Irated= 19A, Isat = 33A.
Where would I find a better suited inductor that won't exceed maybe +20C rise under these conditions? It can be toroidal wound, space isn't a big issue. Digikey seems to only have SMD inductors.