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BQ25155: How to calculate battery pack temperature by NTC?

Paul Yeh
Genius 14945 points
Part Number: BQ25155

Tool/software:

Hi team,

My customer would like to calculate battery pack's temperature via NTC.

But we need equation or tool for this task.

Please help to share tool for us.

Thanks

  • 0
    TI__Genius 14575 points

    Hi,

    To learn more about the BQ25155's TS function you can reference the "Thermal Parameters" section of this app note. Additionally, you can use this tool to help calculate TS parameters and resistances. Please let me know if you need any additional clarifications.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Genius 14945 points

    Juan,

    Thanks for your material. And it is helpful to further understand our chip's design.

    And my customer currently would like to know real battery pack temperature based on ADC data.

    How to translate ADC data to real temperature via their Host?

    In your material, I didn't see it, please help

    Thanks 

  • 0 in reply to Paul Yeh
    TI__Genius 14575 points

    Hi Paul,

    You can use the ADC TS functions to convert the ADC bits into voltage:

    Once you have the voltage present at TS you can use the ITS_BIAS current to calculate the resistance where VTS / ITS_BIAS = RTS. RTS may be equal to RNTC if only an NTC is connected to the TS pin. If you have compensating resistors it may be more complicated, but the objective is to solve for RNTC.

    You can then use your NTC's characteristics to calculate the temperature based on the calculated resistance and the expected resistance for your NTC across temperature. For some NTCs a reference resistance at various temperatures can be used. For other NTCs, the parameters can be plugged into the NTC formula to solve for temperature:

    For this formula R is calculated resistance, R0 is calibrated resistance, B is the NTC beta value, and T0 is the temperature for the calibrated resistance.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    TI__Genius 14945 points

    Juan,

    Thanks for explanation and guidance.

    BRs 

  • 0 in reply to Juan Ospina
    Prodigy 10 points

    Hi Juan,

    Could you please use the table in the datasheet as an example to demonstrate the calculation?


    I applied the above formula to the 'WARM' row (with a temperature of 45°C), but the result I calculated doesn't match the values shown in the table.

    Thanks

    Best Regards,

    Howard

  • 0 in reply to Howard Yu
    TI__Genius 14945 points

    Howard,

    As I know the its_bias is fixed, so you should use 80uA(typical)

    And I know in your circuit, there is 10kohm resistor in parallel with NTC, so actual effect resistor should be included (10kohm+NTCin parallel)

    Thanks

  • 0 in reply to Howard Yu
    TI__Genius 14575 points

    Hi Howard,

    As Paul mentions, additional external resistances should be taken into account when calculating R. ITS_BIAS is a fixed typical 80uA bias current so you should expect to use that about that much current.

    If there is a 10kOhm resistor in parallel with the 4903.4 Ohms of calculated NTC resistance, you'd expect to see about 3.29 kOhms of resistance at TS, indicating a ITS_BIAS of about 80uA with a voltage of 0.265 V.

    Best Regards,

    Juan Ospina