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ADS1178: Use Vcom as Vrefp

Anders Gjeruldsen
Prodigy 20 points
Part Number: ADS1178


Hi,

I designing a board using the ADS1178 and was wondering if Vcom (through an Opamp) can be used as a 2.5V positive reference at Vrefp, or would it introduce any major problems?

If some of the input channels are used in a single ended configuration, could Vcom also be connected to AinN?

Thank you in advance!

Best regards

anders

  • 0
    TI__Mastermind 48510 points

    Hello Anders,

    Welcome to the TI E2E community.

    Yes, you can use a buffered version of Vcom to drive the reference.  However, this output is simply a resistor divider, and will change with AVDD.  In addition, the typical accuracy is 1%, so this will directly increase your gain error from 0.1% to 1% or more, plus the tolerance of the AVDD supply.  We do not have any data for temperature drift, or min/max specs for Vcom.

    If you need a single ended input, you can also drive the AINN pin with Vref to get a full scale range of +/-Vref differential.  So yes, you can also buffer Vcom and drive the AINN input as well.

    I would suggest using a precision reference if you need DC and/or gain accuracy, but if you are just looking for AC performance, then you could use the Vcom to eliminate a separate reference.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 20 points

    Dear Keith,

    Thank you for the response, it was just what I needed to know.

    Best regards

    Anders B. Gjeruldsen