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ADS127L01: Is strictly necessary to use an FDA to drive it?

Fernando Prokopiuk
Prodigy 80 points
Part Number: ADS127L01
Other Parts Discussed in Thread: THS4551, , PGA113, LM358

Hi,

I want to make a design to evaluate the ADS127L01, with a single-ended imput. In the datasheet  suggest to use an FDA, the THS4551. I want to know if it is strictly necessary to use it, i was thinking to use a PGA113 to drive de ADC.

Thank you, 

Fernando

  • 0
    TI__Guru 66156 points

    Hola Fernando,

    An FDA is not strictly necessary to drive the ADS127L01. However, an FDA can accomplish two things for your single-ended input signal that you may find beneficial:

    1. The FDA can take a single-ended input and create a differential output of the same magnitude (i.e. +/-2V in, +/-2V differential out).
    2. The FDA can also shift the input signal such that the differential output is centered around a reasonable common-mode voltage (typically mid-supply). This will maximize the voltage swing on each ADC input pin and utilize the ADC full-scale output code range (see Figure 58 in the ADS127L01 datasheet).

    The ADS127L01 is also an unbuffered ADC, which means that the input pins connect directly to the switch-capacitor sampling stage of the delta-sigma modulator (as opposed to a high-impedance amplifier input). Driving unbuffered ADCs differentially yields better distortion performance due to equal settling on each input pin.

    If you were to drive the ADS127L01 with a single-ended buffer, both the output common-mode voltage of your signal as well as AINN should be set to mid-supply. This produces what is known as a "pseudo-differential" measurement (see Figure 59 in the ADS127L01 datasheet).

    Best Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 80 points

    Hi Ryan,
    Thanks for your answer. I understand the benefits of use a FDA driver, but I don’t have one in this moment, so I would use a single-ended buffer. As the input kneed to be buffered, I was thinking to use a LM358 in a noninverting buffer configuration, that would work to produce "pseudo-differential" measurement?