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ADS8638: Best voltage for HVSS and HVDD for long term use

Vetea Paul
Prodigy 10 points
Part Number: ADS8638
Other Parts Discussed in Thread: TLV4171

Hi,

I am using an ADS8638 in my design to read +/-12V analog signal, it's working good with HVSS = -15V and HVDD = +15V. However I could save some money and space by using a +/-12V power supply for HVSS and HVDD.

But my question is, is it better for the quality of the signal integrity, for the quality of the AD conversion and for the reliability to stay with the +/-15V in order to not always be at the limits of the component which would be the case with +/-12V ?

Thus, could I have some problem using +/-12V for HVSS and HVDD to read a +/- 12V analog signal ?

Thank you for your help

  • +1
    TI__Guru**** 174266 points

    Hi Paul,

    Welcome to our e2e forum!  Yes, you can use +/-12V for HVDD/HVSS however you should look at the amplifier needs that you might have in front of the ADS8638 inputs.  You may need overhead in the drive stage ahead of the ADC inputs to realize the +/-12V full scale input using the external 3V reference requirements.

  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    Thank you for your reply,

    I am using a rail to rail AOP TLV4171IDR powered with the same +/- 12V, here's my schematic.

    Does that make sense to you for this ADC ? To have a good accuracy even at 12 or -12V. I already used this schematic by the past but with +/-15V instead of +/-12V

    Thank you for your help

  • 0 in reply to Vetea Paul
    TI__Guru**** 174266 points

    From the front page of the TLV4171 datasheet: "These devices can operate with a full rail-to-rail input 100 mV beyond the top rail, but with reduced performance within 2 V of the top rail."  Can you wire up your +/-15V version with +/-12V rails and give it a try?  I suspect you might start to see some linearity errors beyond +10V input. 

  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    oh yes I did not see that I agree with you. I will give it a try to verify but I think you are right.

    So if we assume that I would have a perfect rail to rail AOP which can work perfectly on its full range, it would be ok for the ADC to be powered with the +/-12V and read a +/-12V signal with good accuracy on the full range.

  • 0 in reply to Vetea Paul
    TI__Guru**** 174266 points

    In an ideal world - yes.

  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    Ok that was what I wanted to know with the ADC now I can study what we do for the input considering our specifications and choose if we stay with the +/- 15V

    Thank you a lot Tom