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Original question:

ADS1220: Alternatives to Analog Device AD7730

ADS1261: Alternative to Analog Device AD7730 and issues with ADS1263

Riccardo Villani
Intellectual 1185 points
Part Number: ADS1261
Other Parts Discussed in Thread: ADS1263,

Hi guys,

my customer have been using the AD7730.

Thanks to your recommendation we suggested the ADS1263 but the customer preferred to test the ADS1261EVM. He has some questions:

First problem: the offset register is unique, for internal and external calibration. Perform an initial calibration without laod. During normal operations it is not possible to continuously calibrate the offset to compensate for drift,carrying out an "internal calibration", which would override our offset, since the initial offset register contains our "tare".It therefore becomes necessary to store the offset in the external control system and continuously calculate the offset.

Second problem, and more serious: full scale calibration is not possible.It is not possible to calibrate the full scale with an "internal calibration" method because the converter does not have this function,it is not possible to calibrate the full scale with a "system calibration" method because our signal is too small.
With the GANCAL calibration command, the FSCAL calibration register takes the value 1FFFFF, therefore out of scale (<106%)
The converter works quite well, but these calibration errors make it problematic if not impossible to use.

Could you help us? 

Thank you
Riccardo 

  • 0
    TI__Mastermind 45715 points

    Hi Riccardo,

    The most effective way to correct the offset error is using the offset system-calibration with SYOCAL command by shorting the input to the system which can remove the system level offset errors. 

    The easy way to do full-scale calibration is, you can simply connect the reference source to your inputs for a PGA gain of 1V/V. Please refer to the method described here which is used for ADS1263 also can be used for ADS1261:

    ads1263: Self Calibration vs. User Calibration

    One more thread related to the calibration for ADS1261:

    ADS1261: Full Scale Calibration

    Notice that we always recommend performing offset calibration before full-scale calibration.

    Best regards,

    Dale