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Original question:

BQ79731Q1EVM-060: Calibration paramater in bq79731 or bq79718

BQ79731Q1EVM-060: Power management forum

junyoung kim
Prodigy 15 points
Part Number: BQ79731Q1EVM-060

ADC calibration is in progress regarding bq79718.

1. I would like to know what the internal ADC spec or product name used in bq79718 is.
2. I want to know the ADC calibration method.
(How to resolve or compensate for gain error and offset error)
3. If there is a sample code, I would like to download it. (adc.c file)

  • 0
    TI__Prodigy 540 points

    Hi Junyoung, 

    Are you asking about the BQ79718 or about the BQ79731? 

    Sincerely,

    Michelle W. 

  • 0 in reply to Michelle Williams
    Prodigy 15 points

    I would like to know how to calibrate the voltage before or after reading it. For example, I would like to know about the self and system calibration register or any user guide if the hardware is calibrated internally.

  • 0 in reply to junyoung kim
    TI__Prodigy 540 points

    Hi Junyoung, 

    Apologies for the delay, the BQ79718 should be ready to use without any additional calibration from the user. Specifically for the ADCs, you can look at pg 32 of the datasheet under section 7.3.2.1.5 to find what is configurable for the ADCs. You should only need to convert the register value to the correct voltage using the LSB value (i.e. Vlsb_standard). 

    Sincerely,

    Michelle W. 

  • 0 in reply to Michelle Williams
    Prodigy 15 points

    Thank you for answer.
    To summarize, in order for the user to read the correct voltage, all they have to do is change the Vlsb_standard register without separate calibration, right?

    Could you tell me more details about vlsb_standard and how to set the Vlsb_standard value?
  • 0 in reply to junyoung kim
    TI__Prodigy 540 points

    No, the Vlsb does not need to changed nor can it be changed. It is the value in the datasheet that defines what voltage the least significant bit of the register translates to. All that needs to be done is to take the (ADC register value)* (Vlsb) to find the correct voltage. For example, to read the ADC in GPIO5, you would take the value read from the GPIO5_HI/LO register and multiply it by the Vlsb standard. If you need help enabling ADCs, please refer to Operations Control portion of the Measurement System section of the datasheet. 

    Sincerely,

    Michelle W. 

  • 0 in reply to Michelle Williams
    Prodigy 15 points

    Michelle W, thank you for your always kind answers.

    To summarize, when reading voltage using bq79718, the user can use it without additional calibration, and there is a method to read the correct voltage (for example, VCELL18_HI/LO register value * Vlsb). Is that correct?

    So what happens if an error occurs in the Vcell18_lo register value?

     

  • 0 in reply to junyoung kim
    TI__Prodigy 540 points

    For you first question, yes! For all conversions, refer to table 7-3: Measurement Conversion Equations in the datasheet

    For your second question:

    - If you are referring to when the ADCs read back a value different than expected but are running, that could be caused by external or system noise. You can digital low pass filters to the VCELL and GP ADCs to reduce system noise as detailed starting pg 24 & 25 of the datasheet. Depending on the conditions of your device, you can adjust these setting as needed.

    - If you are referring to when the ADCs read back as 0xFFFF or if an error flags on the device, that means the ADCs are not configured correctly or are not ready. Looking at Table 7-5. ADC Ready/Status Table in the datasheet is a good start to check that ADCs are functioning correctly. 

    Sincerely,

    Michelle W.