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AD7193 AINx Current Issue

Question asked by mcohan on Jun 1, 2017
Latest reply on Jun 9, 2017 by JellenieR

I'm in the prototyping phase of developing a product and am using the AD7193 (the EVAL-AD7193EBZ, specifically). I've run into an issue where the analog input current is an order of magnitude higher than what the datasheet specifies. I'm using channels AIN1 and AIN2 to measure the voltage of a battery and when I put an ammeter in series with the positive lead of the battery I measure ~10uA static current, not the 1 or 2 nA I expect per the datasheet. The ammeter is a calibrated Keithley 7 1/2 digit multimeter with nanoamp resolution and accuracy.

 

Some details on the ADC setup/configuration:

-Configuration Register Word: 0x803018 (differential mode, unipolar mode, buffer enabled, AIN1/AIN2 and AIN3/AIN4 enabled)

-Mode Register Word: 0x59801E

-ADC in Idle mode

-Battery voltage ~3.6V (5V reference)

 

At first I thought I damaged the ADC input protection diodes but I'm still seeing uA range input current after replacing the IC with a new one and installing 1kohm series protection resistors to limit the diode current if the ADC inadvertantly sees an overvoltage. I don't know if I'm missing something obvious but I am out of ideas and need to get this resolved. Thanks in advance for any help anyone can offer.

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