Tool/software:
Input voltage = 17Vmax 12Vmin (4S Lithium Battery)
Output Current 1-2A max on both outputs 5V & 3.3V
We have extensively tested this circuit in the lab without issues, but now having ~30 failures/1000 units in the field. What we're seeing is a failure on power-up when 17V is initially applied to the input. The 5V rail either does not come up at all or it fails shorted. Note these were working units that left production and worked fine for months. After replacing only the TPS55383, the units work fine again.
Things that come to mind?
- ESD maybe? I have attempted air discharges to input/output and see no failures
- Reverse polarity? not possible with the connector system
- Inrush? the built-in soft start should prevent any damage, but I have a test fixture running now continuously cycling power with an added 1000uF on the 5V rail and see no issues.
- Bad comp network? Not sure if that's possible, since all works as expected, except for these random failures?
- Bad layout? It's pretty clean, 4 layer board, good ground planes, tight loop, but same also wouldn't we see this failure during development?
- Wrong Inductor? they are IHLP2525CZER100M01 "FIXED IND 10UH 3A 105 MOHM SMD" which seem fine for the application - I believe they were ok per the calculator
Any other ideas? Thanks!
