Other Parts Discussed in Thread: BQ24765
We have observed some failures on the LMZ21701 converters we are using in our product. So far, on 100 boards assembled, we have seen 3 regulators fail into service. On all of these failed devices, the output of the regulator show a low impedance (in the 1 to 2 Ohms ballpark), a very low voltage at the output and PG pin stays low.
When we removed the regulator, we could confirm that the low impedance (short) comes from the regulator itself.
The issue is very similar to what was described here: https://e2e.ti.com/support/power-management/f/196/p/528460/1922132
About the application: Our device is used in a railway environment. The board use 5 of these converters, arranged in a row. All of these are supplied from a regulated 12V or a Li+ Battery supply, so the input voltage can be anywhere from 6 to 12V. a BQ24765 handles the power path management and the charging of the battery.
The power these converters have to deliver is quite low, between 0 and 110mA at either 1, 1.2, 2.5 or 3.3V.
The schematics and layout is below.
Its there any obvious issue with our design? What should I do to track down the issue?