Looks like I called the game a little early. On the breadboard I was using Ground as the -IN input and +-12V as the +IN input, and got the expected results. Now that I am trying it with -IN at 2.5V and +IN with a 0-5V square wave, the output is, again, not what I expected. When +IN is 0V, output drops all the way to the negative rail, so that is good. But when it is 5V, I am only getting ~3.5V on the output, not 12V from the positive rail.
Using an Analog Discovery, I've hooked up the chip to try to characterize the behavior I am seeing. It looks as if the output voltage when +IN>-IN is proportional to +IN. Isn't it supposed to go up to the V+ power supply?
Attached is the output from the Analog Discovery. Its power supply only supports +-5V, so I've scaled down the square wave and reference voltage to be proportional to the 12V case. When +IN is 2V and -IN is 1V, Out is only .6V. Here's a table with the voltages I've tried so far:
+IN, OUT
2V, .6V
4V, 2.6V
5V, 3.6V
What am I doing wrong? Why does it seem like OUT is just a 1.4V voltage drop from +IN when +IN>-IN?