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ADS7952: 2xVref input range with REFP=2.5V and VA=3.3V

Brian West
Prodigy 60 points
Part Number: ADS7952

The datasheet states that the absolute max voltage on CHx to AGND is VA+0.3V. If VA=3.3V then it should be no problem to apply 3.3V to CHx, but will the ADS7952 have any issues converting the channels while REFP=2.5V and the range is set to 2xVref?

I do see that the full scale input span and absolute input range specifications are 2*Vref but the test conditions note that is only for "Range 2 while 2xVREF ≤ +VA" and there's no mention about what happens when 2xVref > VA. Just wondering if this is an easy way to increase the measurable input voltage range without having to generate a separate 5V rail from the main 3.3V supply.

Thanks!

Brian

  • +1
    TI__Expert 6731 points

    Hi Brian,

    Thank you for your question!

    If VA=3.3V, then yes, 3.3V can be applied to CHx. If REFP=2.5V and the range is set to 2xVref, then there will be no issues during conversion. Using a range of 2xVref will be needed when your inputs are 3.3V. This is because using a range of Vref=2.5V (smaller than input voltages) will cause the ADC to saturate.

    There is no problem if 2xVref > VA, as long as your input voltages (AINP or CHx) do not surpass the absolute voltage rating (VA+0.3V). By using a CHx of 3.3V and a 2xVref (5V) range, you will get correct output codes, but the codes that represent an input signal level greater than 3.3V will remain unused. Unfortunately, there is no way to increase the measurable input voltage range with the same 3.3V supply.

    Best,

    Samiha