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ADS127L11: Single ended, unipolar use question

Adam Porsch
Intellectual 375 points
Part Number: ADS127L11
Other Parts Discussed in Thread: THP210, OPA140

Tool/software:

I have an application where I'm required to use the ADS127L11, where it receives a single ended signal, ranging from 0V to about +2V. The idea I have is below:



I've used this ADC before, along with a THP210, where the THP210 accepts a bipolar, differential input voltage, resulting in a high quality measurement.

Here, while being required to use the ADS127, I don't have the performance demands as the fully differential measurement circuits.

I'm curious if I'm understanding the ADS127L11 datasheet correctly, that for unipolar power supply configs, with a single ended input, I can tie AINN to GND, and feed my buffered positive voltage to AINP.



I'm thinking about using an OPA140 for the buffer.

If I understand it, worst case, I'll lose the 1 bit and only be able to read 23 bits:


Thanks for the clarification.

  • 0
    TI__Mastermind 43001 points

    Hi Adam Porsch,

    You are correct in your assessment. The ADS127L11 can accept single-ended inputs if AINN = GND = AVSS. You will lose a single bit of performance because the ADC code range is bipolar, but you will only be able to use the positive half of the range.

    Alternatively, you could connect AINN = 2.5V, then your input would swing around this voltage. Any voltage <2.5V applied to AINP results in a negative code, while any voltage >2.5V applied to AINP results in a positive code. Using VREF = 2.5V in this case allows you to use the full ADC code range, assuming AVDD = 5V.

    These statements assume you are following the Recommended Operating Conditions with respect the to AINx and REFx pin voltage requirements of course.

    -Bryan