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LM5117: Output drop at high Vin

Part Number: LM5117

I purchased a LM5117 and designed a circuit board almost identical to the one in the datasheet on pg 22 on the datasheet (also pg 10 on the LM5117 Eval board).  The only difference is that I used CSD19537Q3T fets.  It is on a PCB and I tried to keeps caps close, etc.

I also have an eval board to compare/contrast.  Eval board is at 12 V, mine is set for 5V out.

My board works well for 0-5 A loads with an input voltage of 18-21 V. No good at 36 V input.  The weird thing is that in mid-range voltages, it dips, then comes back. 

Digging down on loading at 26 V in, a hysteresis occurs.  The drop is precisely at 0.469 A, and is reproducible 

I've taken more traces and checked more pins than I can convey.  But here is one trace that seems to indicate the problem.

This is the SW pin with 24 V in, 3.87 V out, and a 1.1 A load.  Seems that every other pulse collapses.

I would appreciate any perspective.  I've been pounding on this for 2 days.