What does the "Output Voltage Swing vs. Load Resistance" signify? Lets say I want to get a gain of 400 from an op-amp. I can use any one of the following combination
Gain = -(R2/R1)
Case 1: R2 = 400 Ohms; R1 = 1 Ohms -> Gain = 400 Case 2: R2 = 40000 (40K) ohms; R1 = 100 Ohms -> Gain = 400.
From op-Amp perspective, does the above scenario do something different?
Picture of "Output Voltage Swing vs. Load Resistance" for AD712 is attached below
When load resistance decreases, current increases (assuming voltage is fixed). By the looks of it, the opamp you are dealing with can only provide 25mA of current.
In order to ensure that the load doesn't try and source or sink more than 25mA, the graph you provided just shows what the suitable voltage levels are for your resistance.
For instance, lets say your load is 100 ohms. The maximum current you can draw is 25mA. So
$$ V = IR $$ $$ V = 25mA * 100 ohms $$ $$ V = 2.5V $$
Which what you're graph is showing.
So instead of doing this calculation for every single load, they have done it for you.
All this plot is telling you is not to go over 25mA.
Added
Found this in the datasheet
What does the "Output Voltage Swing vs. Load Resistance" signify?
It tells you that if you have a 10 ohm load the maximum peak-to-peak voltage you can faithfully produce at the output is a bit less than 1Vp-p. For a 100 ohm load this rises to about 3Vp-p. For an open circuit load this becomes about 28Vp-p. This assumes power rails are +/-15V.
With a feedback resistor of 400 ohms, this is likely the load seen at the output due to the inverting input being a virtual earth so expect an output voltage no greater than 17Vp-p.
