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ADS1243 Vref, Range_bit and Calibration

ROBERT BONINI
Intellectual 390 points
Other Parts Discussed in Thread: ADS1243

In reading the datasheet for the ADS1243 there seems to be a bit of ambiguity about acceptable Vref ranges and calibration.

Page 18 of the datasheet states: "The RANGE bit (ACR bit 2) must be zero during calibration."

On the same page is the following set of restrictions: 

• For VDD = 5 V and RANGE = 0 in the ACR, the differential VREF must not exceed 2.5 V.
• For VDD = 5 V and RANGE = 1 in the ACR, the differential VREF must not exceed 5 V.
• For VDD = 3 V and RANGE = 0 in the ACR, the differential VREF must not exceed 1.25 V.
• For VDD = 3 V and RANGE = 1 in the ACR, the differential VREF must not exceed 2.5 V.

I would like to use a VDD = 3.3V and a VREF = 2.5V.  This appears to be allowable with the RANGE = 1 however during calibration, RANGE = 0.

Is it allowable to have the above voltages with RANGE = 0 during calibration?

  • 0
    TI__Guru* 97775 points
    Rsbonini,


    You should be able to use the reference with RANGE=0 just during calibration. This is for your case of VDD=3.3V and VREF=2.5V

    During calibration, the ADS1243 tries to measure the reference so that it compares the input and reference sampling to ensure the proper gain error. The RANGE bit affects this comparison, so it should be set to 0 during calibration.

    Once the calibration is completed, set the RANGE bit to 1.

    The reason for the limitation of the external voltage reference is that the performance and accuracy may suffer if the VREF is large with the RANGE bit is 0, The linearity takes the biggest hit to the performance.


    Joseph Wu