AnsweredAssumed Answered

AD8221 - output intermittently goes negative when both inputs close to 0V

Question asked by ElectronAby on May 16, 2012
Latest reply on Jun 11, 2012 by ScottH

Hi,

 

I have an AD8221 setup to read a sensor of input 0 to 1V DC. The gain is set to 3.5. The sensor -ve output is connected to -ve i/p of amp and +ve is connected to +ve i/p of amp. The ref of amp is conneted to +0.1V. I have LP filters on the inputs of the amp consisting of 4.02K Res and 10nF caps with a 100nF cap across the two i/p pins.

 

The circuit seems to sometimes work fine when i/p is > about 0.5V. When +veinput gets closer to 0V the output of circuit starts to go negative, but it is sometimes ok. It is itermittent. Touchng the amp or componets around it seems to trigger the problem and touching again fixes it!

 

At the output pin of the amp i have a 20K res and 1uF cap LP filter configuration.

 

Any ideas would be appreciated. I have tried adding resistors for bias current path but this did not help.

 

Please HELP!! I am desperate for a solution.

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