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ADS1262: Accuracy over temperature

Caleb Swieson
Prodigy 110 points
Part Number: ADS1262
Other Parts Discussed in Thread: TIDA-00550,

Hello, I have an universal external sensor input module that I'm designing with an AFE based on the reference TIDA-00550. I have a custom board and software working, but am getting accuracy results over temperature much worse than the reference design.

I have done gain compensation at room temperature only, and am getting errors around 0.05%FSR at room (which is acceptable for the application). Over temperature the error goes up to 0.9%FSR at 85C (while the reference design stays within 0.05% throughout).

The graph is representative of the results I am getting. It is current measurement from -20mA to +20mA, with a PGA of 4. The accuracy results are pretty much the same regardless of whether I am measuring voltage or current. They are also the same regardless of the PGA value.

I am looking for any ideas or further testing to do in order to narrow down the cause of the additional errors.

Thanks,

Caleb

  • 0
    TI__Intellectual 1300 points

    Hi Caleb,

    Is the burden resistor a low temp drift?

    Can you also explain how you calculated the %FSR?

    Also, did you measure the input current with an independent DMM, i.e. was the source current constant over temperature?

    Thanks,
    Lars

  • 0 in reply to Lars Lotzenburger
    Prodigy 110 points

    Hi Lars,

    Yes, the burden resistor is low temperature drift. Since the error graph is also very similar for the voltage measurements, I'm pretty sure that's not the issue.

    For the %FSR error I just took the absolute error (in volts or amps) and divided by the FSR of the selected mode.

    The source is generated by a multifunction calibrator that was outside the temperature chamber, and was also measured by a DMM outside the chamber.

    Caleb

  • 0 in reply to Caleb Swieson
    TI__Intellectual 1300 points

    Hi Caleb,

    can you please re-run the setup with PGA 1V/V? The 32bit converter gives you still enough resolution with the expected input range of ~0.5V. Furthermore, the influence of the internal reference is reduced. Also, how is your AVDD-AVSS supply changing over temp?

    Thanks,
    Lars

  • 0 in reply to Lars Lotzenburger
    Prodigy 110 points

    Hi Lars,

    Here are two graphs: the first is measuring current with PGA = 1, the second is measuring voltage with PGA = 1. My calibrator can only output 24.1mA, while the FSR with the PGA=1 is 91.2mA.

    I have not measured the analog supply over temperature yet. I can check that out. Would a varying Analog supply cause this?

    Regards,

    Caleb

  • 0 in reply to Caleb Swieson
    TI__Intellectual 1300 points

    Hi Caleb,

    Seems PGA=1V/V improved the result for the current input.
    Did you enable the chopper for the measurements? During my measurements this feature was enabled.

    My calibrator can only output 24.1mA, while the FSR with the PGA=1 is 91.2mA.
    I think it is ok here to calibrate at ~25%FSR.

    I have not measured the analog supply over temperature yet. I can check that out. Would a varying Analog supply cause this
    The ADS1262 specifies PSRR of 80dBmin for the analog part. See also section 8.4 of the ADS1262 datasheet. As the power supply voltage most likely does not change much, it will also not much contribute to the error. I would be anyway interested in AVSS-AVDD at 25C and 85C.

    Can you please send me some raw data (DMM and ADC codes) to see whether I get the same error results?

    Thanks,
    Lars

  • 0 in reply to Lars Lotzenburger
    TI__Intellectual 1300 points

    Hi Caleb,

    I haven't heard back from you. Hope you could resolve your issue. If not just let me know.

    Thanks,
    Lars