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ADS1220: PGA settings

Shivam Trivedi
Prodigy 45 points
Part Number: ADS1220

Hi,

I am trying to program ADS 1220 through arduino board. But i am not able to set its PGA (Programmable Gain Amplifier) through programming. I am choosing different PGA values i.e 1,4,16,32,64,128. 

At all the values of gain i am getting same corresponding output value. How should i configure the values.

  • 0
    TI__Guru** 113765 points
    Hi Shivam,

    Welcome to the forum! When the gain is changed for the ADS1220, the full-scale range changes as well, but the code value reported should show a value relative to full-scale range that reports the input voltage. So the output code reflects the value of the input voltage applied. In the value for a single code the formula is +/- VREF/GAIN/(2^24-1). Note how changing the gain reflects value of the LSB size (or value of a single code). Changing the gain doesn't change the value reported, but rather increases the discernible resolution.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 45 points

    Hi Bob,

    Thanks for your reply. Further can you please share your code with me for setting PGA.

    Thanks,

    Shivam

  • 0 in reply to Shivam Trivedi
    Prodigy 45 points

    Hi Bob,

    Can you please share the solution with us as to what change we should do to observe the change in output voltage by changing the gain value in the program.
    I am using ADS 1220 code.
    Thanks,
    Shivam

  • 0 in reply to Shivam Trivedi
    TI__Guru** 113765 points

    Hi Shivam,

    There is some example code for the ADS1220 found here:

    https://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/2635.ads1220-example-code

    One way of checking if the gain settings are changed is to read back the register contents after writing.

    Regarding the input voltage, you must apply a differential input voltage within the correct common-mode for the PGA when enabled.  If you apply a ground referenced signal (single-ended) you will be outside of the common-mode specification when the PGA is enabled.

    When you say you want to see a change in the output voltage, there is no way to directly monitor this integrated solution.  The output of the PGA connects directly to the analog to digital converter (ADC) which outputs the value as digital data.  If the register setting is changing for the PGA, then you should see an increase in the returned code.

    Please send me all the register settings you are using, the schematic, and scope or logic analyzer shots of the communication.  In particular I need to see shots of the register write.  Also, it would be helpful to know what voltage you are applying to the inputs and what result data you are seeing.

    Best regards,

    Bob B