Not familiar with the Melexis part however the first thing I would verify is if the A/D input is working? Could try a 1.5 V battery to verify.
Also triple check your pinout is correct. Don't just look again. I've found if I make a wiring error each time I check it I'm sure its correct. I have to do something different to catch my mistake.
Perhaps print out the pinout from the data sheet and hold it next to your circuit.