Hello Robert, When using bipolar supplies, connect REFN to AVSS, or -2.5V. The reference circuit should also be referred to AVSS. In this case, you can use either 2.5V or 4.096V reference values. The evaluation board uses the REF6225, which works well for AC signals and higher bandwidth inputs. For best DC performance, the new REF54 devices will provide better DC accuracy and lower noise near DC (lower 1/f noise). For any of the below reference options, you will want to enable the REFP buffer inside the ADS127L18 for best performance. 2.5V options: REF6225 REF54250 4.096V options: REF6241 REF54410 Regards, Keith Nicholas Precision ADC Applications
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