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Vcom on ADS1278 for differential input

Qi Tang
Intellectual 370 points
Other Parts Discussed in Thread: ADS1278

Hi,

As specified, Vcom has half of AVDD(So Vcom is around 2.5V as I use 5V for AVDD) and can be used for Vocm(output common-mode voltage) of a differential opamp.

My question is, why not using Vref (I use REF5025 for 2.5V) instead of Vcom as I think it is more accurate. What is the difference?

Thanks,

Qi

  • 0
    TI__Mastermind 46290 points

    Hi Qi,

    So long as the REF5025 output is buffered I think this scheme could work and save you a buffer coming off of the Vcom pin from the ADS1278.

    In general terms it is better to keep the reference voltage isolated from the rest of the system, if you can afford the space and cost of another amplifier I think it would be a happier design. Accuracy of the common mode voltage shouldn't be a huge concern. It's just a vehicle to satisfy the converters inputs and shouldn't have a tremendous impact on your conversion results.

  • 0 in reply to Kevin Duke
    Intellectual 370 points

    Great, Thanks for the answer.

    Qi