AD7788 increase the input range

Good day!
Read of theme "AD7788: Input ranges"
I have a question to the expert answer.  In documentation for REF3040 I found a similar circuit.

A specialist in the above subject, a similar connection recommended AIN- input to expand the input voltage. However, in the specifications for REF3040 input voltage range has not changed. Where the error lies?

Thank you!

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    •  Analog Employees 
    on Nov 20, 2016 6:34 PM

    Hi Ocela,

       As mentioned on the AD7788 datasheet it can have a unipolar and bipolar ranges. The Ain+ input can be referred to the Ain-. As an example, when using 2.5V on Ain-. The input voltage range is from 2.5V to 5V but when it is in bipolar mode the range will be from 0V to 5V. You can program the U/B bit in the mode register to select a unipolar /bipolar input. ADI has 2.5V reference voltage sources recommended like the ADR381 and ADR391. If you have other questions, please let us know.

    Regards,

    Jonathan

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  • 0
    •  Analog Employees 
    on Nov 20, 2016 6:34 PM

    Hi Ocela,

       As mentioned on the AD7788 datasheet it can have a unipolar and bipolar ranges. The Ain+ input can be referred to the Ain-. As an example, when using 2.5V on Ain-. The input voltage range is from 2.5V to 5V but when it is in bipolar mode the range will be from 0V to 5V. You can program the U/B bit in the mode register to select a unipolar /bipolar input. ADI has 2.5V reference voltage sources recommended like the ADR381 and ADR391. If you have other questions, please let us know.

    Regards,

    Jonathan

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