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ADS1271

MOUHAMED AMINE LOUSSIF
Prodigy 40 points
Other Parts Discussed in Thread: ADS1271

dear

does any one know how :

Vrefp max = ?

Vrefn max =?

FSR max = ?

because i have to measure a 230Vrms signal then i have to scale it down ....

  • 0
    TI__Mastermind 45250 points

    Mouhamed,

    It is important to remember that the ADS1271 measures the differential voltage between AINP and AINN (Vin = AINP – AINN).

    The data sheet states that Vref can be between 2.0V and 2.65V (with 2.5V being the typical value used).

    Vref = VREFP – VREFN (from data sheet)

    VREFP can be between VREFN + 2.0V to AVDD – 0.5V (from data sheet).

    VREFN can be between AGND- 0.1V to VREFP - 2.0V (from data sheet).

    Taking this into account you can see that VREFN has to be at least 2.0V from VREFP and VREFP can be a maximum of AVDD – 0.5V.

    With this in mind:

    If AVDD is 5.0V then VREFP could be 4.5V maximum.

    If VREFP was 4.5V then VREFN must be between 1.85V to 2.5V.

    For FSR let’s use 4.5V for VREFP and 2.0V for VREFN.

    Thus Vref is 2.5V (4.5 – 2.0 = 2.5V).

     With Vref at 2.5V the maximum measurable differential voltage will be 2.5V.

    The ADS 1271 measures the difference between AINP and AINN (AINP – AINN = Vin)

    If the voltage level on AINP is 2.5V higher than on AINN (full input +) then the output from the converter will be 7FFFFFh.

    If the voltage level on AINN is 2.5V higher than on AINP (full input -), then the output of the converter will be 800000h.

    I hope that this answers your question.

    Richard Elmquist