Hi,
I'm currently struggling with an INA321 that seems to be showing symptoms that somewhat resemble instability (the output is drifting in a sinusoidal manner, though only slightly [around 300uV pk-pk at a gain on 10V/V]). Though I can't seem to identify any cause for the instability.
The device is configured as follows. A Wheatstone bridge is connected to the same supply as the the INA321, which is 2.7V. The Common-Mode Input sits around 1.35V with a maximum differential voltage of 9.45mV maximum.
In trying to figure out what could be causing the issues with the instrumentation amplifier I have managed to confuse myself with regards to the acceptable input voltage range for the device. Could someone please help me understand the section of the datasheet explaining the common-mode input voltage range?
Here is what I understand and can figure out:
1) "The upper limit of the common-mode input range is set by the common-mode input range of the second amplifier, A2, to 1.2V below positive supply."
1) This would mean the upper limit would be 1.5V (would this be correct?)
2) "The lower limit of the input range is bounded by the output swing of amplifier A1, and is a function of the reference voltage according to the following equation: VOA1 = 5/4(Vcm)-1/4(Vref)"
2) VOA1 = 1.6875V-1/4(Vref)
If I have a low Vref, say 15mV this would mean VOA1 = 1.68375V. How does this help me to work out if my input is within the common-mode input range?
3) If I look at the graph on page 6 everything seems to be fine, but I'm unsure if I'm interpreting it correctly.
Thanks for your help in advance,
Gavin