This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1271 temperature response

Other Parts Discussed in Thread: ADS1271

Hi,

I am using an ads1271 and I noticed a nonlinear temperature response. When I connect the two differential input to the Vref and change the temperature from 30-80 deg.

This is the record of the temp and digital data

Red-ads1271 temperature

Perpol-ads1271digital output

Green- 60 samples averaging

 

 You can see that in about 75 degree the grape starting to decline and at 80 deg going back up again.

This is a major problem for my system is there any solution?

  • Hi Daniel,

    Thanks for your question and welcome to our E2E forum!

    First, I would like to confirm a couple details about your setup:

    1. Is the y-axis on the left-hand side reporting the output code value from the ADS1271?
    2. What are you measuring in this graph and how are the inputs configured?

    To me, it looks like you are measuring the offset voltage of the ADS1271 over temperature. The offset drift is given as a typical spec of 1.8uV/C, which translates to about 100uV or 335 codes of change in offset over the span of 55 degrees C (assuming Vref = 2.5 V). If other components on your PCB are drifting over temperature as well, you might notice additional deviation in the ADS1271 output.

    The temperature seems to be changing quickly. Is this expected in your application? Would you be able to perform periodic offset calibration to account for the offset at a given temperature?

    Best Regards,

  • Hi Ryan,

    Thanks for your quick replay.

    1. Yes, y-axis is the output code value from ADS1271

    2. In this measurement as you said I’m trying to measure the offset voltage of the ADS1271, and I understand that the drift is within normal rang but the problem is in its shape because we do 2’th order compensation, this temperature response we can’t compensate.

    The vref temperature drift has been tested alone and found proper.

    For the temperature quick change it’s only for the test but the problem occurs at a slow temperature change as well.

    this is the input config at the test:

    Regards,

  • Hi Daniel,

    Do you measure the reference voltage and the ADS1271 offset simultaneously? As the reference drifts, the LSB size of the ADC will change as well, which will affect your conversion results. Therefore, it is important to measure the reference and the input together as you sweep the board temperature.
  • Hi Ryan,

    I don’t have the means to measure the voltage reference at the required accuracy but instead I tried to use 2 different voltage reference chips including one that I have experience in a similar system and the results are the same so I think it’s safe to assume that the voltage reference is not the cause.

    Have you run tests similar to mine and didn't see this behavior?
  • Hi Daniel,

    I do not doubt the absolute accuracy of your voltage reference. I was implying that as your system temperature increases, your voltage reference also increases due to drift. Both of your reference chips probably drift by about the same amount. 

    In the schematic above, the differential input to the ADC will stay around 0V (+/- offset), but the output of the ADC will vary as VREFP varies with respect to GND. To compensate, you must measure VREFP simultaneously and convert the output codes accordingly.

    Does this make sense?