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Why is REF5040 suggested in the ADS1158 datasheet?

Alex Mastro
Prodigy 95 points
Other Parts Discussed in Thread: ADS1158

On page 42, Figure 54 of the ADS1158 DS, I  do not understand why REF5040, a 4.096 reference, is suggested as the voltage reference for the ADS1158.  The DS says full-scale input to the ADC is 2.133.. * VREF.  When the analog inputs are limited by AVDD and AVVS = +/- 2.5 V, isn't this 4.096 V reference twice as large as it needs to be?

  • 0
    TI__Mastermind 44720 points

    Hi Alex,

    The inputs to the ADS1158 are fully-differential, but you can also use single-ended inputs.

    In the example in figure 54, a single-ending input may reference AIN0 to AINCOM. Notice AINCOM is grounded and AIN0 can only swing +/-2.5V. In this case, you are only using about half of the ADC's input range, and yes, the reference is about twice as large as it needs to be.

    If instead you used differential inputs, (AIN0 and AIN15 for example), then both of these inputs could swing +/-2.5V and your total differential input signal becomes +/- 5V. In this case you take full-advantage of the ADC's input range and achieve the best resolution of your input signal (I'm assuming a 5V reference here for simplicity).

    With a 4.096V reference connected to the ADS1158, you can only apply a differential input of about +/-4.369V. Typically the input signals would be limited to about +/-2V where the internal PGA is the most linear (away from the supply rails).

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    Prodigy 95 points

    Hi Chris,

    This makes perfect sense, thanks.

    Alex