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Measuring Bipolar Inputs With ADS1220

Abdullah Ghamdi
Prodigy 60 points
Other Parts Discussed in Thread: ADS1220, LM4040

Hi

I am planning to measure bipolar signals that swing between +2V and -2V using ADS1220. In the schematic, AVDD is tied to +2.5V rail and AVSS is tied to -2.5V rail. I am using an external 2.048V reference (LM4040) that goes into REFP0, but what about REFN0? is it proper to connect it to ground AND be able to measure both positive and negative inputs?

Best Regards,

Abdullah

  • 0
    TI__Guru** 113765 points

    Hi Abdullah.

    Welcome to the forum!  First of all you, you are not required to use an external reference as the ADS1220 has an internal reference of 2.048V.  Using the internal reference saves you having to add external components and allows you the same range of measurement.  If you do use the LM4040, then the easiest connection would be to connect the shunt reference across the reference inputs where the cathode would connect to REFP0 and the anode connects to AGND and REFN0.  The reference would be supplied by AVDD through a current limit resistor.  The connection configuration is similar to the LM4040 datasheet figure 12.

    In general the full-scale range of the ADS1220 is +/- VREF and you can measure any voltage within the range of AVDD and AVSS (+2.5V to -2.5V in your configuration) as long as you stay within the reference range.

    Best regards,

    Bob B