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ADS131E08: Relation of input range vs. AVDD

Shota Mago
Expert 8130 points
Part Number: ADS131E08

Hi team,

My customer provided some questions in terms of input range for ADS131E08.

What if input Vinp=2.5V/Vinn=-2.5V under Vref＝5V, AVDD-AVSS＝±2.5V?

Does ADS131E08 can output code7FFFFF if it recognize above input as differential input=5V?

Or ADS131E08 can't accept Vref=5V since AVDD=2.5V from GND?

I look forward to hearing back from you.

Best regards,
Shota Mago

  • 0
    TI__Guru* 97805 points
    Shota-san,


    If the supply is bipolar (AVSS=-2.5V, AVDD=+2.5V), then the reference voltage can still have a magnitude of 5V, but you would connect VREFN=-2.5V and VREFP=+2.5V. Because the reference is an analog input, the absolute max will be AVDD+0.3CV, and the operating max is AVDD.

    This information is written into the Recommended Operating Conditions table on page 7 of the datasheet. Under the section of Voltage Reference Inputs in the table, VREFN can nominally be AVSS while the max operating voltage for VREFP is AVDD.

    So if AVSS=VREFN=VINN=-2.5V and if AVDD=VREFP=VINP=+2.5V, you should be able to read an output of 7FFFFFh.


    Joseph Wu
  • 0 in reply to Joseph Wu
    TI__Expert 8130 points

    Hi Joseph-san

    Thanks for your explanation.

    Though I've verified answer, let me confirm my understanding.

    If VREFP=2.5V and VREFN=-2.5V, it means VREF=2.5-(-2.5V)=5V

    In this case, when the customer uses Pseudo-Differential input,  full scale range should be 5V.

    On the other hand, full scale range should be 10V(±5V) when Fully-Differential input.

    Is this understanding correct?

    Best regards,

    Shota Mago

  • 0 in reply to Shota Mago
    TI__Guru* 97805 points
    Shota-san,


    That is correct. If VREFP=2.5V and VREFN=-2.5V, the VREF=2.5-(-2.5V)=5V and the full scale range of the ADC is ±5V. Also if the customer uses a pseudo-differential input (such as AINN=0V, but AINP can go from -2.5V to +2.5V), then the input seen by the ADC will be ±2.5V of measurement.

    In that setup, the ADC range is ±5V, but the pseudo-differential input is ±2.5V, and the customer will only see half of the full ADC range.


    Joseph Wu
  • 0 in reply to Joseph Wu
    TI__Expert 8130 points

    Hi Joseph-san

    I understood.

    Thanks for your kind explanation!

    Best regards,

    Shota Mago