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ADS122C04: Question about reference voltage and input range

Simon Mali1
Prodigy 130 points
Part Number: ADS122C04

Hello

I would like to use ADS122C04 in one of my applications for input voltages +-2.048V or less. I am power suppling with +-2.5V on analog part and 3.3V on digital part. Will I have the range from -2.048 to +2.048V with using internal reference voltage which is 2.048V? This is the case where I use AIN0, AIN1 and AIN2 as voltage input AINp and AIN3 connected to 0V (GND) as AINn. In this combination 3 channels out of four. What happens with the input range if I use AIN0..AIN3 as AINp and internally connect all AINn to AVSS which would be in my case -2.5V? In this case I have all four channel available.

Best regards

Simon Mali

  • 0
    TI__Guru** 112935 points

    Hi Simon,

    The answer to your first question is yes.  When using the internal reference with a gain of 1, your full-scale range is +/- 2.048V.  Whether the outcome is positive or negative depends on the AINP input relative to the AINN input.  If AINP is greater than AINN then the conversion result is positive.  If AINP is less than AINN then the conversion result is negative.

    If you use the internal connection where AINN is connected to AVSS, then your reduce your measurement to just the positive range of up to 2.048V above AVSS (-2.5V).  If the sensor output is relative to GND, then you would have a very odd outcome and would not be able to measure the desired range.  The measurement would be from AVSS (-2.5V) to AVSS+2.048V (-0.452V).

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 130 points

    Hi Bob

    Thank you very much for your answer.

    Best regards

    Simon