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ADS131E08 REFERENCE

Qi Tang
Intellectual 370 points

Other Parts Discussed in Thread: ADS131E08EVM-PDK

Hi,

I am using bipolar scheme which connects AVDD to +2.5V and AVSS to -2.5V and DVDD to 3.3V. I am confused by the reference connection.

According to the spec, looks like we connect VREFP to GND and connect VREFN to -2.5V, this way I believe we use internal 2.4V reference;

But if I want to use REF5025 for external 2.5V, the spec says VREFP max limit is AVDD which is +2.5V, so it is not good to connect it to VREFP. How should we connect the external reference if we want to use it? Or in this situation we only choose internal reference?

I definitely need help on this.

Thanks and best regards,

Qi

  • 0
    TI__Mastermind 23235 points
    Hello Qi -
    You can reference the EVM schematic in the ADS131E08EVM-PDK on page 37 for clarification on the reference connection. An external reference is shown, U2 or U3 (along with the buffer), as an example. VREFN should always be AVSS. VREFP will be the reference voltage which will be referenced to AVSS.
  • 0 in reply to Greg Hupp
    Intellectual 370 points
    Hi Greg,

    Thanks for the quick reply! I studied the page37 before but I still have concern.

    if I connect VREFN to -2.5V (AVSS), VREFP to +2.5V reference, then Vref = (VREFP-VREFN) = 5V which exceeds AVDD 2.5V specified by in page 3 of the spec.

    Best regards,

    Qi
  • 0 in reply to Qi Tang
    TI__Mastermind 23235 points
    Hello Qi -
    If you connect the reference IC with respect to AVSS and AVSS is -2.5V, for a reference IC that generates 2.5V, as long as you connect VREFP to reference output and VREFN to AVSS you will get VREF = 2.5V. VREF = VREFP=VREFN, where VREFP = ~0V and AVSS = -2.5V.