Background: I have housekeeping power supply circuit using a LM5160 flybuck providing an isolated and non isolated 12V output. These separate outputs both power a LMZ21701 each to provide 5V outputs as well. The intermediate 12V may or may not be loaded as needed. This circuit is similar to www.ti.com/.../tidrhw3.pdf sheet 3, and for a similar application.
Operating Issues: Failure of either LMZ21701. Both the isolated and non-isolated devices have failed in different prototypes, mainly while investigating other downstream power converters. I am presuming I have an over-voltage occurring on the inputs to either on the LMZ21701, although this is not confirmed. The result is a shorted output. on the LMZ21701. The input to the switcher is 12V. When attempting to remove the component from the pcb, the inducotor on top of the chip got removed from the chip too. This inductor measures open. I can only image what happens to the internal FETs in the inductor is open.
Questions: What are the failure modes for this chip? Would an over-voltage support the failure hypothesis? Is there some other extreme that could damage the device in this fashion. If there is an over-voltage at the input, will the LMZ21701's failure mode protect the 5V output circuitry from over-voltage?
