TIDM-02014: OPA320AQDBVRQ1

Vu Thien,

When I open TIDM-2014, I do not see the diagram you show in your post.  So, my analysis is based on the schematic excerpt only and not the document:

The linear operating range of an op amp is limited by its supply voltages.  This linear operating range can be limited by output-swing or common-mode specification of the amplifier.  The OPA320 common-mode is rail-to-rail ( -0.1V to 3.4V in this case).  The output swing limit depends on the load current (resistance).  In the given schematic, I assume the device is driving an ADC.  Thus, I assume the load current is fairly low.  You can look at the OPA320 output swing specification to see how close the amplifier can swing to the supply rails.  In this case, it is 10mV typical and 20mV maximum (see below for RL=10k).  However, this is the saturation limit of output swing.  As you approach this limit the signal will become distorted.  A more conservative (low-distortion) limit can be found by looking at the AOL specification test condition.  This condition says that AOL will be good (Min =114dB, Max =132dB) when Vout is within 0.1V of the supply rails (see below).  Thus, for this circuit configuration I would expect the amplifier's worst case saturation limit to be:  20mV to 3.28V (20mV limit), and the low-distortion conservative range to be  0.1V to 3.2V (0.1V limit in AOL).

I believe the document is likely referring to factors outside of the op amp (e.g. the input from the shunt, and the ADC limits).  The op amp itself will not have the significant limits of 0.33V to 2.97V mentioned in the image.  Op Amp Input and Output Swing Limitations document explains the concepts discussed above.

I hope this information is helpful to you.

Best regards, Art Kay