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ADS131E08: Dual Supply and external reference

Alberto S. G.
Prodigy 100 points
Part Number: ADS131E08

Checking the datashhet of ADS131E08, Im having doubts about my schematic...

Im reading 8 differential channels.

I have these levels in my circuit:

AVDD=+2.5v

AVSS=-2.5v

VREFP=2.5v external

VREFN=-2.5v

VREFP=AVSS+2.5V that means VREFP=0... Shall I tie VREFP to DGND?
If I would like to use internal reference, Can I use both Vref 2.4V and/or 4V?

  • +1
    TI__Mastermind 45845 points

    Hi Alberto,

    The actual reference voltage (Vref) is generated with respect to AVSS and the VREFN should be always shorted to AVSS, so the reference voltage is the difference between the  VREFP and the VREFN. When an external 2.5V reference voltage is connected to the VREFP pin, your Vref is VREFP-VREFN=2.5V-(-2.5V)=5V for +/-2.5V bipolar power supply. 

    According to the specification shown in the datasheet, Your external reference voltage can not exceed AVDD which is 2.5V for your bipolar power sully, however you can still achieve a 4V Vref if you can provide an external 1.5V reference voltage to the VREFP pin, your Vref=VREFP-VREFN=1.5V-(-2.5V)=4V, or you can use either 2.4V or 4V internal reference voltage.

    I hope this can help you understand.

    Regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 100 points

    As I understood in your explanation if my external reference would be 2.5V my Vref do not would excede AVDD. It would be equal , it should work, isnt it?

  • 0 in reply to Alberto S. G.
    TI__Mastermind 45845 points

    Hi Alberto,

    Correct, external 2.5V reference should work.

    Regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 100 points
    One more question Dale,
    Should I refer the external reference (2.5V) to AVSS? In my case I refer it to the same GND that I refer AVSS (-2.5V)

    Regards,

  • 0 in reply to Alberto S. G.
    TI__Mastermind 45845 points

    Hi Alberto,

    Please see my answer below. Why do not you use internal 2.5V or 4V voltage reference on the E08 ADC?

    • If you voltage reference output is referred to the AGND which is shorted to the GND of the ADC, your Vref is VREFP-VREFN=2.5V-(-2.5V)=5V.
    • If you voltage reference output is referred to the AVSS of the ADC, your Vref is VREFP-VREFN=2.5V

    Regards,

    Dale