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.
I think Matt is on to something, but the AD8567 is a quad. Look at the AD8542. It's a cheap dual that should get
within 20-30 mV of ground sinking 100 uA. See figure 22 on the AD8542 datasheet.