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AD8223B reference input voltage clamping

Question asked by BertD on Jun 21, 2011
Latest reply on Jun 22, 2011 by BertD

I'm working on a design that's going to be using an AD8223B inst amp, however in my breadboard circuit, I can't seem to get the reference voltage to go below about 0.61V.  I'm using it in a single supply configuration with Vs = 12V.  The gain resistor is 3.09kohm.  The input is a differential voltage of approximately 8mV with a common mode voltage of approximately 5V.  The reference circuit consists of a voltage divider feeding an op amp buffer that directly feeds the reference pin on the AD8223.  When I put a potentiometer on the input of the buffer to vary the voltage on the reference pin, I see the voltage clamp at about 0.61V.  Changing the input of the op amp buffer does not result in a lower voltage at the reference pin.  I'm trying to set the voltage to approximately 0.25V for my configuration. 

 

The datasheet indicates the voltage range for the reference pin as -Vs to +Vs with a 5V single supply, however for my configuration this doesn't seem to be the case.  Is the datasheet correct?  Any help would be greatly appreciated.  Thanks. 

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