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ADS114S08: About single-ended input

kenta
Prodigy 80 points
Part Number: ADS114S08
Other Parts Discussed in Thread: ADS1120

Hi,

I would like to use the following connection with ADS114S08 and use it with single-ended 0-3.3V input voltage. Is there a problem?

AVDD = 3.3 V
AVSS = 0V
REFP1 = 1.65 V
REFN1 = 0V
AIN1 = 0 to 3.3 V (MUXP)
AIN 0 = 1.65 V (MUXN)

In this case, is the following code?

AIN1 AIN0 VDiff Dec Hex
0V 1.65V -1.65V -32768 8000h
1.65V 1.65V 0V 0 0000h
3.3V 1.65V 1.65V 32767 7FFFh


best regards.

  • 0
    TI__Guru** 113765 points

    Hi Kenta,

    That is a doable use case with the PGA bypassed and your table is correct.  If you want to use the PGA at a gain of 1, your input range would be limited to (AVDD-0.15V) to (AVSS+0.15V).

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 80 points

    Hi Bob,

    Sorry, there was a lack of explanation.
    I want to enable and use PGA.
    I want to use gain at 2 or more.
    Can I use gain of 2 or more for single-ended input?

    Best regards,

    kenta

  • 0 in reply to kenta
    TI__Guru** 113765 points

    Hi Kenta,

    Your original use case was a pseudo differential input with an input range of 0 to 3.3V at AINP.  For this use case the PGA must be bypassed and only a gain of 1 is possible.  To use the PGA, whether it be a gain of 1 or higher, the absolute input range is reduced to between (AVDD-0.15V) to (AVSS+0.15V).  The range narrows even more if you use a gain greater than 1.  The input range is given in section 7.3 of the ADS114S08 datasheet.  A ground referenced single-ended input would violate the input range using a unipolar supply.

    You could use bipolar analog supplies (+/- 2.5V) which would allow a single-ended ground referenced input using the PGA and gains greater than 1.  But in this case you would not be able to measure a 3.3V input.

    Perhaps you can tell me more about what you intend to do and I can be of more help.  You might also take a look at the ADS1120, which will allow the PGA to be bypassed along with a possible gain up to 4 in bypassed mode.

    Best regards,

    Bob B