common thermistor 76920

The bq76920 energizes the thermistor ~ 50 ms every 2 s to make a voltage reading.  The part does not communicate when it is making the reading, so the external circuit would need to monitor when the bq76920 is energizing the thermistor and avoid that time.  The TS1 input should be OK with a voltage applied by the external circuit during operation as long as it is within the recommended and abs max limits for the pin.  Keep in mind that if the other circuit applies a voltage while the bq76920 is shut down, the bq76920 will boot if the voltage is sufficient.  Also note that to boot the bq76920 the TS1 voltage must go from low to high, so if the external circuit holds a residual voltage on TS1, the bq76920 will not be able to boot after shut down (ship mode).

The bq76920 does not have protection thresholds associated with the temperature measurement, so collisions between the 2 circuits should not cause a hardware protection event, but the system software would need to discard any readings from collisions.  A common controller could determine which circuit should energize the thermistor, but be aware of the 2 second interval for the bq76920 measurement and the uncertainty of the switching command in that timeline.

In many cases a second circuit is used for redundant checking of the system. Using a common thermistor may be undesirable as it creates a dependency of one circuit on the other.  You may find it best to use separate thermistors.  If the system does not need to be redundant, sharing may be ok.  You might also consider if the internal temperature sensor on the bq76920 is useful although this would be the part temperature (board temperature) rather than having the potential to be remotely mounted (cell temperature).