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Unexpected output from AD8237

Question asked by PeterT on Jun 11, 2013
Latest reply on Jun 18, 2013 by ScottH

Hello,

 

I am using an  AD8237 to provide a common mode voltage to a signal in order to measure it with an AD7794. Please see the attached circuit for details. The problem is that the output voltage is not always as expected. Most of the time a get the correct output voltage but after power cycling a couple of times the output jumps up to a wrong value.

 

For examle:

 

Vsupply+ = 5 V

Vsupply-  = 0 V ( AGND )

Vref        = 2.50 V

Vinput+  = 1.3 V

Vinput-  = 0 V  ( AGND )

 

The expected output voltage is 3.8 V which is observed most of the time but after  power cycling a couple of times the output jumps up to 4.8 V.

Any idea what I am missing ? Do I misinterpret the  allowed common mode ranges ?

 

Thank you!

Peter

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