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BQ76940: Temperature Measurement with Thermistor

Yusuf KAYA
Intellectual 630 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ78350-R1, BQ78350

Hi,

My design is BMS which uses BQ76940 AFE and BQ78350-R1 and there are 3 pcs of NTC (RT1, RT2, RT3) for temperature measurement on the circuit. At the beginning, the circuit was getting temperature value via 3-thermistor then i removed 2 pcs of it (RT1, RT2) from circuit and replaced again. After that, I see temperature value 157C on both RT1 and RT2 on BQ Studio Software Interface. Is this a failure or correctable things with parameters in software? 

Would you please help me solve the problem immediately?

Thanks.

  • 0
    TI__Guru 54715 points

    Hi Yusuf,

    A high temperature with the NTC indicates a low resistance, such a very low resistance may indicate the thermistors are shorted. 

    The internal pull up resistor is 10k expecting a 10k at 25C NTC.  Parameters may be adjusted in the BQ78350-R1 for variations in the thermistor used, see the BQ78350 family thermistor coefficient calculator in the BQ78350-R1 product folder "Design & development" tab.  There is also an offset calibration available for temperature in the BQ78350-R1, however if the change occurred with removal and replacement of the thermistors I would suspect the value is wrong or shorted.