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Pros and cons of Unipolar/Bipolar power supplies for ADS1299?

Alexander Zorn
Prodigy 70 points
Other Parts Discussed in Thread: ADS1299

Is there any reason that the ADS1299 can be powered with a unipolar supply, AVDD = 5V & AVSS = 0 V, or a bipolar supply, AVDD = 2.5V, AVSS = -2.5V?

Why would one pick one method of supplying power over the other? Thanks!

Alex

  • 0
    TI__Guru 66166 points

    Hi Alex,

    In terms of performance, there really is no difference.

    I think what you need to be concerned with is the acceptable voltage ranges for your input channel pins. With a single-ended supply of 0-5 V, your input pins will not be able to take singles below ground; instead, they will be saturated and the output will read "negative full-scale."

    Bipolar supplies avoid this concern and allow each input pin to receive voltages above and below ground.

    If you expect your input signals to have a large common-mode, you can use the "patient bias drive" amplifier to adjust the common-mode of your inputs to within the AVDD-AVSS range.

     

    Thanks and regards,

  • 0 in reply to Ryan Andrews
    Prodigy 50 points

    Hi Ryan, please explain how to configure VREFP when we use bipolar power supply+-2.5V.

    If VREFN=AVSS=-2.5V then we need to apply +2.5V reference from external source to VREFP?

    Or we can configure internally to obtain right non-saturated readings?

    Regards

  • 0 in reply to George Mamijs
    TI__Guru 66166 points

    Hi George, 

    With +/- 2.5 V supplies, you have the option of using either an internal or external 4.5 V reference. The internal reference is 4.5 V +/- 0.2%.

    Using the external reference, as you alluded to, would require applying an external voltage to VREFP. Keep in mind the requirement that VREFP = AVSS + 4.5 V. With +/- 2.5 V supplies, VREFN = AVSS = -2.5 V, so you cannot apply more than +2 V on VREFP.

    Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 50 points

    Hi Ryan,

    Thanks for full answer.

    Please answer just last little question for understanding.

    If we have VREFN=-2.5V and VREFP=+2V does this mean we have unbalanced inputs?