Consider the scenario of using two TPS25944L eFuse devices to perform power multiplexing as per Fig 79 of the device datasheet (copied below).
The Primary Supply V(IN1) is a 5V DC regulated power source.
The Auxiliary Supply V(IN2) is a 4.5V non-rechargeable battery for backup purposes (three AA 1.5 V cells in series)
Let suppose the Primary Supply V(IN1) fails i.e. due to complete failure of the external Primary Power supply unit.
In this case it seems to me that PGOOD will go low as long as there is some residual V(IN1) to keep the internal circuitry of the upper TPS25944L running. Up to this point fine, since PGOOD will go low and instruct the lower TPS25944L to connect IN2 to the System Load as expected.
Soon, though, when V(IN1) reaches and stays zero and the internal circuitry of the upper TPS25944L stops working, it seems to me that PGOOD will be forced back to high by the pull up resistor R5 since the devices' internal FET will no longer be able to stay ON to keep PGOOD low.!
When this happens, the lower TPS25944L managing IN2 will now see on its OVP input a rising voltage level through R5 and when it exceeds the OVP threshold, the lower device will block IN2 from reaching OUT.
Inevitably OUT voltage level will drop and when it drops below the OVP threshold the lower TPS25944L device will reconnect IN2 to OUT.
This will be repeating in an oscillating way, i.e. the lower device will keep connecting and disconnecting IN2 to/from OUT until the Primary Supply (IN1) is fixed/replaced.
Apparently I am missing something here. Please advice how we can maintain IN2 steadily connected to OUT until IN1 is restored.
Looking forward to hearing from you.
Kind Regards.
