EVAL - AD7746EB with AN-1585

Hi, 

I'm working with the AD7746 evaluation board, but I'm having problems to couple the extending of the capacitive input range of the AD7745 / AD7746 (application Note: AN-1585), I did the calculations as mentioned in sheet 3 of AN-1585 datasheet, but when the program is running only marks me the maximum value and does not change when I modify the capacitance. (It is for a level sensor).

The capacitor I am using is 150pF empty, I put a capacitor in series to leave a capacitance of 17pf and be able to measure it only by adjusting the CAPDAC as mentioned in datasheet 21 of AD7746, but the SW only shows me a value of -4,096 that does not change even if I modify the capacitance only changes to maximum (+ 4,096pF) when the capacitor in short circuit.

How much capacitance can be adapted using the extending capacitive input range (AN-1585)?

Thanks in advanced