I am giving more details about the problem . pls read patiently.
we are using p-MOSFET's ORing to do automatic switchover b/w @ 12V_External (comes from PCIE edge) and emergency battery.
The circuit is as follows. We have testing with different slew rates on 12V_External (@ CIN - comes from PCIe edge). at slower slew rates(~ ms) this works as intended. But when we tried with 35us ramp-up rate on 12V. we are seeing ~11V spike on Battery (presently we used DC power supply for battery) during turn ON of 12V_External.
This spike is not seen with other slower ramp-up rates.
I will explain little more details on this.
When 12V_EXT power ON, VBATT ON --> 12V_PLOSS will be LOW & 12V_SLOSSN will be HIGH - power feeds from 12V_External
When Power off on 12V_External, @ 7.015V of 12V_External, 12V_PLOSS becomes HIGH (at this 12V_SLOSSN is still HIGH) so, no power is goes to 12V. when 12V_External reduces 6.715 12V_SLOSSN starts swicthing and becomes LOW Turns ON VBATT MOSFETs (M2) - which then powers the 12V.
Now, when power came back, when 12V_External reaches 6.715V 12V_SLOSSN becomes HIGH( at this 12V_PLOSS is HIGH) so, again no power goes to 12V. when 12V_external reaches 7.015 12V_PLOSS switches LOW now power comes from 12V_External to 12V.
Above is the regular scenario.
Now the problem is>>>>
When Power comes up 12V_External with faster slew rate, there is path from 12V_External to VBATT because of that VBATT is increasing --> as 12V_SLOSSN,12V_PLOSS thresholds are depend on Battery voltage , 12V_SLOSSN,12V_PLOSS are switching @ higher 12V_External voltage.
One more thing, when M1 OFF & M2A,M2B ON - there is a path from 12V_External to Battery through Body diode of M1. But Vf of body diode is 0.8 to 1.2V, Since 12V_SLOSSN siwtches @ 6.715V, Vf of Body diode won't reach as per design.
any help will be useful.
any thoughts on this?
I doubt dv/dt false Turn ON on M1 - But not sure how to find it.