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BQ76905: Cannot get to TS Pin to provide correct Temperature Data

Anand Nateshan
Prodigy 40 points
Part Number: BQ76905


Tool/software:

Hello,

I have connected a 10k Ohm NTC to the TS pin and am trying to read the data from the Pin, however the temperature reading I am getting is incorrect. I have NOT connected any Pull Up resistors since in the TRM, it said that there is an internal pull up.

I am also unsure how I need to process the data I get from the TS pin. Should I be using a look up table to convert the data into degrees Celcius, or is there another way?

I am using an STM32 as the main MCU in my system. Any help here would be much much appreciated. I have been stuck on this for a couple of days now.

Thanks you very much,

Anand

  • 0
    TI__Mastermind 42070 points

    Hello Anand,

    The TS pin only reports the result value as a raw ADC measurement where each LSB = 92-uV. You would have to characterize your thermistor to get an accurate temperature rating.

    See Section 7.4 TS Pin Operation of the TRM:

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 40 points

    Thank you Luis for your quick reply.

    I have looked at this many times and my circuit looks exactly as shown. 

    I am just unsure how to implement this into my code? how can I use the 91uV to change it to temperature? Any help here would be much much appreciarted.

    Furthermore, my IC is referenced to a differerent GND than my STM32. They do not share power or GND, due to the system architecture. Will that have an effect on the measurement data or does that not matter?

    Thank you Luis for your help and your time,

    Best Wishes,

    Anand

  • 0 in reply to Luis H. S.
    Prodigy 40 points

    Hello Luis,

    Furthermore, there are some inconsistencies in the TRM. If you look at section 7.4 and the second paragraph, it says "When the bit is set, the TS pin operates in thermistor measurement mode." Whereas when you look at the table showing what ever bit in the DA Config register does, it is exactly the opposite (Table 12-5). 

    Do I need to do anything with the DA Config register or can I leave it as it is in default?

    Thank you,

    Best Wishes,

    Anand

  • 0 in reply to Anand Nateshan
    TI__Mastermind 42070 points

    Hello Anand,

    Good catch. I will bring it up and it will be corrected. Follow Table 12-5, that is correct and can be left at default.

    Anand Nateshan said:
    I am just unsure how to implement this into my code? how can I use the 91uV to change it to temperature? Any help here would be much much appreciarted.

    As I said, you would need to characterize your thermistor. The device will only report the raw ADC values. So you would convert it to a voltage by multiplying the raw ADC value by 92-uV. The pull-up voltage is 1.8-V.

    Best Regards,

    Luis Hernandez Salomon