Customer is doing a daughter card using two LM5067 for two inputs. There’s a daughter card fixed in the chassis and the issue happened when we plugged another daughter card into the backplane. The hot swap on daughter card fixed in the chassis would re-start before the plug-in daughter card turn on the hot swap MOSFET.
Actions on the fixed daughter card, see attached waveforms:
-
I disabled the OVLO pin and pull UVLO/EN pin to VCC pin via 50kohm resistor but it doesn’t help.
-
I monitored VCC pin voltage while it didn’t drop to below 8.4V.
Actions on the hot plug daughter card:
-
There’re two hot swap inputs on the SCH. When customer disabled one hot-swap and the other can startup normally. If customer power up the two hot swap at the same time, there’s a big voltage drop at the input voltage which would cause system shut down.
-
Customer put differential probes on current sensing shunt resistors, then the two hot swap can startup normally. Tried to parallel caps between sensing resistors, but it doesn’t help.
-
Customer put probe on the Timer pins, then the two hot swap can startup normally.