I have a board with four LMZ14203H devices on it. They are all connected two a 28V-34V battery source (that is switched between two sources, primary and backup) using external circuitry. Two of the LMZs are regulating to 6V and two are regulating to 12V. In the end they should be sourcing about 2.5A, but currently when bench testing they are seeing no load as we're just unit testing the board for proper regulation.
We had all four fail on one board and then, when replaced, the two regulating to 6V never regulated properly and the two regulating to 12V failed in the same manner almost immediately.
The failure symptoms are Vin shorted to Vout or Vin shorted to ground or Vin shorted to both.
At this point I cannot figure out if there is a circuit problem, a board layout problem, a device installation/soldering problem, or a device failure problem.
On the same board I have a LMZ14201 regulating the same input rail to 5V that has never failed in all the bench testing, so the problem seems relegated to the LMZ14203H devices.
Has anyone else experienced problems with this device in this manner? At this point I'm considering an emergency circuit redesign using another vendor's parts that has somewhat simpler installation (ie. through hole and no thermal pad underneath) in the event that it is a problem with the installation of the device on the board.
