Tool/software:
I have been using the EN pin for Under voltage detection using the calculations from the Data sheet. This circuit has worked for many builds over some time, but recently the circuit is failing by not starting up. I looked at the EN pin and I can see a noise on the pin related to the switch frequency. Replacing the Converter with alternate sourced and batch device fixes the problem, as does taking the external resistors off the under voltage detection divider (which have been checked for the correct value).
1) Is the EN pin used internally for any other fault detection reset hence the visible noise?
2) Is it possible that there has been a batch issue?
3) Is there a way to check for fake IC?