Strange behaviour of ISL94202 shuts off FETs at 55°C

[martinjaeger]

According to the ISL94292 manual, xT2 can be used to monitor the FETs.

However, the temperature limit of the FETs is not configurable. If XT2M is set to 1 to indicate that it's not measuring cell temperatures, the FETs are still switched off if the temperature at xT2 reaches 55°C and back on when the temperature drops to 50°C again. These thresholds are the same as the default cell overtemperature thresholds, but they don't seem to be read from the same registers.

Below image shows a test where in a first step xT2 (MOSFETs) was heated up (by charging through body diode while discharge FET was off). Afterwards, the external sensor connected to xT1 (Battery) was heated up with a heat gun. As it can be seen, the same error flags are raised (COTF and DOTF). The cell temperature limit is set to 45°C, re-connect to 40°C, which is working fine. The xT2 limits of 55°C and 50°C are not affected.

This strange (undocumented) behaviour of the chip is also confirmed here:
https://renesasrulz.com/general/f/general---forum/15530/isl94202-demo-board-fet-temp-issue

Possible solutions (in hardware):

1. Use thermistor directly wired to microcontroller.
2. Adjust xT2 thermistor network to match desired maximum measured MOSFET temperature.

[martinjaeger]

Interestingly, it's now picking up the same temperature setpoints as the cell overtemperature: