MC33771C Sudden temperature drop on internal temperature sensor

[User221971]

During normal operation of the MC33771C we sometimes see sudden temperature reading drops on its internal temperature sensor that we cannot explain. Do you maybe have an explanation for this?

  

[TomasVaverka]

Hello Edgar,

I have not heard of such a problem before and cannot explain it at the moment. I will have to involve some experts from our BMS team. 

Could you please tell us how many devices you have tested so far and on how many of them you see this behavior?

Also please check for voltage dips or transients during the time of temperature drop and if possible check for any specific chip activity that could be a common trigger.

BRs, Tomas

[User221971]

Hi Tomas,

sorry for the late reply. It took some effort to look at all the data.

From a recent production batch, I found that 13 out of 380 products showed similar dips in temperature measurement of the MC33771C. All dips occurred in an otherwise steady environment (constant current charging, constant current discharging, idle). No similar dips can be seen in other metrics from the MC33771 (cell voltages, balancing, other temperatures etc).

In terms of chip activity, our algorithms run the same polling of information all the time. I do not expect temporal changes in behavior that could have such a significant effect in chip temperature.

Thanks for the support!

[TomasVaverka]

Hello Edgar,

Thank you for sharing additional details. I have already forwarded them to our BMS team and am currently awaiting their feedback. Thank you in advance for your patience.

BRs, Tomas

[TomasVaverka]

Hello Edgar,

Please see below the answer I have just received from our BMS team.

The temperature of the IC can be affected by the cell balancing activity. Perhaps some SW routines are activating/deactivating the CB.

BRs, Tomas

[User221971]

Hi Tomas,

thanks for the suggestion.

We have, however, verified that the chip is not balancing using the CB_DRV_STS