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ADS1232: Output counts

Sreekanth Anegunda
Intellectual 975 points

Part Number: ADS1232

Hi,

We are using ADS1232 for weighing scale application. With 10sps the output data is almost constant, but when we switch off the system and turn on again some times the output count what we are reading is wrong. When the system/ADC is working normally we read ADC count around 14800 but when the issue comes the ADC count what the controller reads is around 86400.

When the controller is powered on, we are pulling down the PWDN pin, after a delay of ~100ms the PWDN pin is made high for ~100ms and again pulled low for ~100ms and then the PWDN pin is made high and then the controller interrupts are enabled to read the ADC data when the DRDY pin is pulled low by ADC. 

We would like to know what is causing the ADC to output wrong reading and how the issue can be solved.

Thanks,

Sreekanth

  • 0
    TI__Guru**** 182601 points
    Hi Sreekanth,

    I noticed that you were working with Bob a couple months ago, describing your 2mV/V load cell. What excitation voltage and gain setting did you end up using? The 100 ms reset pulse should be fine, so no real concern there. Are you also performing a calibration cycle after power up and reset?
  • 0 in reply to Tom Hendrick
    Intellectual 975 points
    Hi Tom,

    Yes, I was working with Bob a couple of months ago.

    The excitation voltage we are using is 5V which is connected to both ADC ref and Load cell. The gain is set to 128, in any condition we are not putting the ADC in standby mode or in low power mode. We are not performing the calibration cycle after power up. The reason for not calibrating the ADC on power up is due to one of the requirement from customer where if we perform the calibration then our final value will be wrong.

    The ADC works fine when we power off and power up the device, but after few power cycles the ADC will give wrong readings. In this case we need to power off the device, wait for some seconds and then power Up the device.

    Thanks,
    Sreekanth
  • 0 in reply to Sreekanth Anegunda
    TI__Guru**** 182601 points
    Hi Sreekanth,

    Have you been able to verify how far down the rails are going between these power cycles? Calibration should not cause errors in your final values. The calibration function does an internal shorted input 'conversion' and then uses that values to adjust the output with an offset correction factor.
  • 0 in reply to Tom Hendrick
    Intellectual 975 points
    Hi Tom,

    Yes, I have checked DVDD, AVDD and REF pin rails and the DVDD pin is going down till 0.9V and when power up it is 3.0V. The AVDD and REF pin are going down till 0.9V and when power up the REF and AVDD pin is 5.08V.

    To over come any issue related to power cycle we are resetting the ADC as soon as the controller is powered up. We have noticed that some times the ADC will output 7FFFFFh/ 800000h after power cycle.

    Thanks,
    Sreekanth
  • 0 in reply to Sreekanth Anegunda
    TI__Guru**** 182601 points
    Hi Sreekanth,

    Have you made any correlation between full scale +/- outputs (the 7FFFFF or 800000) versus the original 86400 and the residual voltage on the rails? Does performing the reset routine in one case versus the other avoid you having to cycle power again, leaving it off for 'some seconds'? It sounds like you are not getting a proper power on reset.
  • 0 in reply to Tom Hendrick
    Intellectual 975 points
    Hi Tom,

    We didn't make any correlation between the full scale output versus the original value as the ADC output was constant for most of the power cycles.

    I think the issue is not with POR. For now we are doing calibration after POR cycle and we didn't get any wrong values after that. We are going to perform more test on the PCB till this weekend. Upon completing the test will share the result with you.

    Thanks,
    Sreekanth
  • 0 in reply to Sreekanth Anegunda
    TI__Guru**** 182601 points
    Great! Looking forward to seeing your test results.
  • 0 in reply to Tom Hendrick
    Intellectual 975 points
    Hi Tom,

    After adding ADC calibration on Power up the issue is resolved.

    Thanks,
    Sreekanth