MP8759 chips failing shorted

DC-DC Power Converters
1

I’ve got a design using three MP8759s to generate +5V, +3.3V, +1.05V from a 12-24Vdc input. The 5V power enable uses a 2.2M pullup to Vin as recommended in data sheet.
+3.3V enable and +1.05V power enable are both driven by an RC circuit to delay their power up roughly 80ms after +5V comes up. There is a 3.3V zener to keep the power enable voltage below 4.5V.

It all works, except that for some unexplained reason the +3.3V and +1.05V regulators are failing with shorted inputs and/or outputs.

Are there any known causes of such failures, and does the above circuit pose any concern?

power supply extract
power supply extract1399×915 107 KB

2

Hello,

Apologies for the delayed response.
Does it work when testing with each one isolated? That would be output of 5V not driving the EN of other two devices.
Additionally, is there a reason why PG is not being used to enable the devices?

Best Regards,
Yu