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BQ79631-Q1: GPIO port accuracy problem

?? ?
Prodigy 60 points
Part Number: BQ79631-Q1

Hello,

  We used GPIO(MAIN_ADC) for insulation detection and found that when the input voltage to GPIO8 is less than 0.045V, the data returned by channel 8 is always 0.045V(The number returned is 0X129), but when the voltage is greater than 0.045V, the voltage value collected is normal ， The resolution used is 152.59 uv/LSB .

  My Problem is My question is how can I collect voltage values less than 0.045V,Are there any configuration items required for the GPIO port of the MAIN_ADC to capture values below 0.045V

I look forward to your reply. Thank you

  • 0
    TI__Mastermind 23410 points

    Hi, 

    Do keep in mind that the input range for the GPIO is recommended to be between 0.2 and 4.8 V. Our test conditions for measuring GPIO accuracy is specified for at least 0.08 V and so we cannot guarantee any accuracy at the range you are asking for. 

    0b010 = As ADC only input

    0b110 = As ADC input and week pullup enabled

    0b111 = As ADC input and week pulldown enabled.

    I recommend trying each of these and seeing if these are able to improve the measurement.

    Also, are you able to provide a block diagram with the resistor values that you're using for isolation detection? These would be R1, R2, R3, and R4. 

    You may need to vary these resistances if they are affecting your pack insulation resistance measurements. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 60 points

    Hello,

    Thank you for your letter , The resistors we use are as follows

     R1 = 2.09MΩ , R2 = 2.09MΩ  R3 = 14KΩ , R4 = 15KΩ

    We tried to configure it as 0b110, and the collected value was about 0.7V. For 0b010 and 0b111, the result is 0.045V

  • 0 in reply to ?? ?
    Prodigy 60 points

    May I ask why the voltage collected after I pull down the GPIO port to the ground is still 45mv instead of 0V

  • 0 in reply to ?? ?
    TI__Mastermind 23410 points

    The 45 mV is most likely due to the R1 and R2 resistors being large. As mentioned in the table in the Insulation Measurement section, if R2, R3, and R4 are too large, there can be inaccuracy due to leakage at ADC pins. 

    Best Regards,

    Anthony Pham