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AD5241M Digtial Potentiometer

Question asked by jessicaballard8 on Sep 11, 2017
Latest reply on Sep 18, 2017 by koushik.kops

I am currently using the AD5241 as the feedback gain resistor of my current to voltage converter. I have already generated the code that programs the digital potentiometer to correctly form a resistance of approximately 7.9kOhms across terminal B and W (data byte: 0x02). I have verified that the resistance across these terminals is 7.9kOhms using an Ohmmeter. 


I apply a small sinusoidal wave to the signal processing circuit and the output of the circuit is connected to an ADC. I connected the terminals B and W to my circuit and should observe an ADC value of roughly 1700 (tested circuit using a 7.9kOhm resistor in replace of the digital potentiometer); however, the value I received was 2300. I noticed that this discrepancy and measured the resistance across terminals B and W again. It was no longer 7.9kOhm, but now 1.6MOhms. I disconnected AD5241 from the circuit by taking away connections from terminals B and W then measured the resistance across the terminal again. It went back down to 7.9kOhms. 


A schematic of the connections/simplified circuit is shown below:


I looked at example circuits in the AD5241's datasheet. Most circuits have the voltage supply connected to terminal A, ground connected to terminal B, and the output connected to terminal W. Seeing this, I also configured the circuit to have the sinusoidal supply connected to terminal A, ground connected to terminal B, and the current to voltage converter circuit connected to terminal W. Connected, the Ohmmeter read 4.1kOhm across A and W considering that when disconnected the Ohmmeter read 7.9kOhm (data byte: 0xFE). In addition, the ADC value reads 890.


A schematic of the connections/ simplified circuit is shown below:


Regardless, the resistance across the terminals is not consistent with its desired value of 7.9kOhm. The resistance value changes once connected to the circuit which is verified with the Ohmmeter and changes in ADC value.