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ADS7138-Q1: ADC Calibration and input offset error

John Garrett
Expert 4220 points
Part Number: ADS7138-Q1
Other Parts Discussed in Thread: ADS7138

Hi All,

I have a customer who has raised some questions on the ADS7138-Q1's input offset error.  Please review and comment:

We plan to use the ADC ADS7138 on a test board to measure the voltage rails from many power supply boards (designed in-house).

The datasheet mentioned the ADC input offset error "post offset calibration" = 2 LSB max.

This means the input offset error is 2 LSB after the calibration. Questions:

  1. Since we only have one test board, do we have to calibrate it each time we test a new power supply board?
  2. If we don't do the calibration, what would be the max input offset error be?
  3. What is the total max error of the ADC for
    1. ADC is calibrated
    2. ADC is not calibrated

Thanks & regards,

John Garrett TI-AFA

  • 0
    TI__Genius 9656 points

    Hi John,

    Thanks for your question! I will look into this and get back to you tomorrow.

    Best,

    Samiha

  • 0
    TI__Genius 9656 points

    Hi John, 

    1. The calibration process may be done once, unless there are changes in temperature or AVDD, in which case the device must be recalibrated. The calibration function works by internally shorting the ADC input to ground an run through the conversion process.
    2. The input offset pre-calibration cannot be defined as it may differ. We recommend calibrating the device, it only takes 16us max. I do have this graph that defines the input offset drift pre-calibration:
    3. The total max error is defined as the root sum square of all the max errors and may be calculated from the datasheet specs. This post offers further information.

    I hope that helps.

    Best,

    Samiha