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ADS1248: Setting MUXCAL during calibration

Chris D
Prodigy 40 points

Part Number: ADS1248

Hi,


I'm using the ADS1248 to measure thermocouples and have some questions about the Self and System calibration modes:

I currently have the following:

AVDD = 5V

AVSS = 0V

REFP0 = 2.5V

REFN0 = 0V


1. During SELFOCAL do I need to set the MUXCAL register to 001 (Offset Calibration) or does the SELFOCAL do this automatically?

2. SYSOCAL requires the inputs to be externally shorted to a voltage near the mid-supply. As we cannot do this with any of our inputs, could we use one of the System Monitors?

3. SYSGCAL requires the inputs to be set to Full Scale. Again, we cannot do this using AIN0-7, are there any options to do this with a System Monitor?


4. If we can only do System Calibration using the System Monitors, is there any point? If the values are factory trimmed, will I actually gain any accuracy by doing a System Calibration with Systems Monitors?

  • 0
    TI__Guru** 101115 points
    Chris,


    I'll just number my responses in the same order as your questions.

    1. The SELFOCAL command will automatically short the inputs together and then take a set of readings to be averaged. You don't need to use the MUXCAL to set the inputs.

    2. I think that using the system monitors defeats the purpose of running a SYSOCAL. Imagine that you have some sort of amplification on the front end of the ADC measurement (not the on-board PGA, but some sort of instrumentation amplifier instead). If you want to zero out the offset of this front end, so you would use the SYSOCAL.

    3. Similar to the previous SYSOCAL, the SYSGCAL would be used to set the full scale of the input measurement. This would be similar to identifying the reference value to set the scale of the measurement.

    4. Generally, I don't think you'd gain any benefit from doing a System Calibration using the System Monitors. While I think the SELFOCAL is useful, gain calibration registers are trimmed so that the gain error is very low. You might get some benefit with a gain calibration, but I think it would be a small marginal improvement.

    Let me know if you have any further questions. If you're working on a schematic, I'd be happy to review it.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 40 points
    Thank you very much. I think it answers all my questions.