This is a follow-up to the original question where it was recommended to add a reset IC at the output of the TPS610981 for power-up because of the >3kOhms load requirement at startup. (Please read the original question first).
I'm still facing problems with this strange "latch-up" of the TPS610981: It seems that if we have a sufficient high battery impedance (e.g. 250 Ohms) the TPS610981 can enter a latchup state where it can not reset from. In operation of a embedded device, this means that if there is a load current and the battery output resistance has a sufficiently high value, the TPS610981 enters a latchup state where it completely shorts and drains the battery. It does not return from this latchup state, not even if you disonnect the load.
The problem can be reproduced with the TPS610981EVM evaluation board:
1) Connect a >3k Ohms (e.g. 3.1k Ohms) load resistor from the output (VMAIN) of the EVM to GND.
2) Connect a power-supply (2.1V output voltage) with a 1k Ohm potentiometer in series to the input of the EVM.
3) Starting at 0 Ohms, slowly increase the potentiometer value to about ~250 Ohms (This simulates increasing battery output resistance).
-> At >250 Ohms, the TPS610981 enters the latchup state. (Input seems to be shorted by the TPS610981)
4) Slowly decrease the potentiometer. Note that the current increases up >100mA while decreasing the potentiometer resistance.
-> At <19 Ohms, the TPS610981 exits the latchup state and returns to normal operation.
This problem is preventing our embedded device to enter the pre-production phase and we would be very happy to receive some pointers on how to prevent from this type of latch-up.