Mahesh -
Keep in mind that the data out is in 2's compliment format. If the MSB is changing, then it could be the data is just varying slightly around 0. 0x7FFFFF is max positive, 0x800000 is max negative.
To get a better idea of your data, you might want to short the inputs together (in which case, you should get ~0V out) or put a known DC voltage on the input.