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ADS1220: Output Data Format

Chuck Jenkins
Prodigy 90 points
Part Number: ADS1220
Other Parts Discussed in Thread: INA823, REF2041

Section 8.5.2 of the data sheet describes the data output format as twos compliment but shows a +/-FS example that would be appropriate for a differential input setup where 0 is mid scale (half the chosen reference).

How is this applied for a single ended input channel where VIN is 0V to Vref.  We are using a 4.096V external reference on REFP0 and REFN0. Same format 8000000 to 7FFFFFF?

  • 0
    TI__Expert 8140 points

    Hi Chuck,

    The negative half of the full-scale range (800000h to FFFFFFh) corresponds to when the absolute voltage at the AINN pin is higher than the voltage at AINP, thus making Vdiff negative (even if the voltages are positive with respect to GND).

    When using a single ended input where AINN = 0V, only the positive half of the FSR is available, from 000000h to 7FFFFFh.

    Best Regards,

    Angel

  • 0 in reply to Angel Rodriguez de San Miguel Bermudez
    Prodigy 90 points

    We started to use the differential nature of the 1220 but ran into protection leakage issues.  Added the INA823 in front with its 60V protection and set its reference to half our 4.096 ADC reference.

    Based on your comment we are going to insert 2.048 (from REF2041, great part) into an unused input and use the multiplexer to connect it to AINn. Now 0V differential into the INA823 gives us 000000h on the ADC output (instead of 3FFFFF if using only the positive side of the AINp-AINn).

    Thank you for the explanation.