When some value in MSB of ads7828 affects LSB also??

Hi,

I am reading analog signal in ads7828E i2c slave ic. Ads7828 returns 2 bytes upon reading data.

i am getting constant value for my constant analog signal til it reaches 255(LSB) when MSB - No value.

but when my input exceeds some value(2.2v), data value exceeds LSB range, i.e there is some value in MSB bytes. when some value exist in MSB bytes its hugely affects LSB bytes. I am not getting - why?? i am using Vdd 5V, Vref - 5v(external)

Kindly suggest solutions for my problem

MY OUTPUT:

VALUE 000543
MSB Value ::: 2  // 512
LSB Value :: 31
VALUE 000543
MSB Value ::: 2
LSB Value :: 31
VALUE 000572
MSB Value ::: 2
LSB Value :: 60
VALUE 000543
MSB Value ::: 2
LSB Value :: 31
VALUE 000560
MSB Value ::: 2
LSB Value :: 48

Thanks

Pon Alagappan