Kelly,

Can you guarantee that your input circuit is well behaved when operated with just a pot ?

Pin 2 of your device is actually NC in the application circuit you have copied.

The "ground" of the device is NOT system ground, which is what you have connected it to. You need a differential input stage to the ADC successfully use this device.

Look at TAOS devices instead, if you have a choice. I am developing a very very low noise photosensor based on their technology.

Steve