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ADS1247 data output is stuck at 7FFFFFh value.

Roman Chak3
Intellectual 460 points
Other Parts Discussed in Thread: ADS1247

Hi, I am using ADS1247 to read analog voltage from a thermocouple. Positive output of the thermocopule is connected to AN0 and negative to AN1.

I configure ADS1247 with the following data:

static const   uint8_t   adc_setup_TC[] = {0x40,0x03, 0x01,0x02,0x40,0x71}; //ADC TC config with VBIAS

I am able to read and verify the configuration data from ADS1247 successfully.

When I read ADC 24 bit output data it is always 7FFFFFh.

What am I doing wrong?

Thank you.

  • 0
    TI__Guru* 97825 points
    Roman,


    First, let's check with the write command: 0x40,0x03, 0x01,0x02,0x40,0x71

    This sequence writes four bytes starting at the 0x00 address with 0x01,0x02,0x40,0x71.

    This will:
    Set the ADC AINP to AIN0 and AINN to AIN1
    Set the VBIAS to AIN1 (to bias the thermocouple?)
    Turn the reference on for conversions and set the ADC reference to to REF0
    Set the PGA to 128 and the data rate to 10SPS.

    I would guess that you have the reference set wrong. When the output data reads 7FFFFF, it means that the ADC is reading positive full scale (or greater). Here you have the reference measuring R39. Without any excitation, this voltage is 0.

    I would instead set the internal reference to be always on, and then use the internal reference as the ADC reference when measuring the thermocouple. I would also try lowering the gain. Start with gain of 16, in case the input signal is very large. To do this, write the following instead:

    0x40,0x03, 0x01,0x02,0x30,0x41

    If necessary, you can put the device in a PGA gain of 1 and measure something other than a thermocouple, just to make sure the device is making a proper measurement.



    Joseph Wu
  • 0 in reply to Joseph Wu
    Intellectual 460 points
    As far as I know the thermocouple needs to be biased. The configuration you have recommended seems to be working.
    Thank you