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CN0287, AD7193, ref input current and error estimation

Question asked by Michael.Konieczny on Apr 1, 2014
Latest reply on Apr 3, 2014 by Wyue

Circuit Note 0287 has AD7193 circuit example, and error estimation follows (PDF page 6).There are leakage currents mentioned, but no mention of reference input current. This current, according to data sheet, is MUCH larger than any leakages. Shouldn't it be also included in error estimation?

If this current is in the range of several hundred nA to even few uA (depenging on ADC, AD7793 has them lower), doesn't it influence the result? Should Vref input be buffered externally, to isolate this input current from measurement branch? Data sheet says that this current is also Vref dependent, so it's not so easy to calibrate/compensate.

Or do I misunderstand ref input current role?