Hi,
I am using the LMZ35003 in a design that operates off 15-50v from lipo batteries to control 12v LED lights. I have built around 25 units to test with and out of those I have seen 4 failures where the LMZ35003 is blown. In these cases the rest of the circuit remains functional after the LMZ35003 is removed.
The LMZ35003 failed in the same way for each of the blown parts. The VIN pin, INH/UVLO pin, and a path to the AGND pad burned up. You can see the damage to two of the LMZ35003 packages in the image below.
The LMZ35003 is configured for a 12v output with an input range of 15-50v in accordance with the example circuit provided in the datasheet.
In all cases where the LMZ35003 blew, it happened when power was connected and the load current draw was < 1A. Since the failures occurred when power was applied, I suspected the inrush current to be the issue. I have measured the inrush current when connecting to a 12S lipo battery on a few modules I have on hand, and it stayed within safe limits. None of the modules I have tested with have blown from connecting the battery yet.
My product is used in a high vibration environment, so my suspicion at this point is that the failures are caused by a broken solder joint. I believe that one of the supporting passive components is susceptible to a broken solder joint and that causes a cascading failure that burns up the LMZ35003. My question is whether this theory sounds likely, and anyone knows which component failing open would cause the LMZ35003 to burn up in the way that it has.
Since all of the failed LMZ35003's have the same damage to the VIN and INH/UVLO pins, I am lead to believe that the broken solder joint is on R11 (schematic in attachments). I believe that if this resistor opens, the INH/UVLO pin will see a voltage too high too handle, then the LMZ35003 will fail. Do you agree with this assumption?
The second component I suspect is C14. If that capacitor is opened, then the LMZ35003 would no longer be configured for slow start, and the inrush current would be much higher than normal.
Since the parts are expensive, I do not want to arrive at the solution through trial and error. Any help you can give me in finding out why these failures have happened would be greatly appreciated.