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BQ25792: About TDIE_ADC accuracy

Tsukui Yusuke
Guru 21930 points
Part Number: BQ25792

Hi,

Could you tell me the accuracy of TDIE_ADC?



Accuracy was good while charging was stopped.
However, TDIE_ADC during charging fluctuated greatly in accuracy.
Accuracy variation is about ±3℃.
Is this result reasonable?

Thanks
Yusuke

  • 0
    TI__Guru**** 166916 points

    Hi Yusuke,

    Unfortunately yes.  We don't spec the ADC accuracy.  The 12-bit resolution setting is no longer recommended.  The higher resolutions will likely skew higher.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Guru 21930 points

    Hi Jeff,

    Thank you for your response.
    >Unfortunately yes.  We don't spec the ADC accuracy.
    I understand.

    Please tell me more about the following.
    >The 12-bit resolution setting is no longer recommended.
    Could you tell me some background that is not recommended?

    Regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 166916 points

    Hi Yusuke,

    We discovered after the IC released that the 12-bit ADC settling time was too short, so it was always reading low.  We used the 12-bit data to characterize the higher bit settings, which measure with long enough settling time.  Therefore, the higher bit readings shifted higher to correct for the 12-bit setting issue.  A new datasheet revision just posted that states that the 12-bit setting is no longer recommended.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Guru 21930 points

    Hi Jeff,

    Thank you for your information.
    Is it similar accuracy for other built-in ADCs?
    Customer does not use ADC TDIE and wants to use external thermistor and BQ25792 VTS ADC.
    If you have any concerns, please let me know.

    Regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 166916 points

    Hi Yusuke-san,

    We do not spec the accuracy of any of the ADC registers for the BQ25792.  13-bit and above will be more accurate but skew higher.

    Regarding using the VTS and thermistor to sense BQ25792 die temp, I do not recommend it because the case temp will quickly exceed the 60C hot TS limit and stop the IC from charging.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Guru 21930 points

    Hi Jeff-san,

    Thank you for your information.
    >Regarding using the VTS and thermistor to sense BQ25792 die temp, I do not recommend it because the case temp will quickly exceed the 60C hot TS limit >and stop the IC from charging.

    Customer wants to use ".REG18_NTC_Control_1 Register  bit 0" to disable temperature monitoring.
    Will ignoring this bit prevent them from being protected?




    Regards,
    Yusuke

  • +1 in reply to Tsukui Yusuke
    TI__Expert 5645 points

    Hi Yusuke-san, 

    Yes, setting the TS_IGNORE = 1 will bypass the temperature monitoring and the charger would assume is safe to charge the battery in all temperature ranges. I do not recommend bypassing the NTC monitoring, unless you have another way to guarantee the battery would be at a safe temperature before enabling charging. 

    Regards, 

    Arelis G. Guerrero