Hi Manoj,
Are you sure you are using the correct conversion formulas? Can you send me the formulas you are using to convert the codes to volts/temperature? Can you also send me the raw digital codes for each of the measurements? The actual returned code will be related to the reference and about 1/4th of the real voltage for the voltage measurements. An internal voltage divider is required to drop the measurement within the correct common mode input range and also the correct full-scale range.
For the temperature measurement, you need to convert the codes to a voltage and then determine the relative difference based on 25 deg C. Lets say you measure 120mV. 25 deg C is 118mV. This is a 2mV difference. The temperature coefficient is 405uV/deg C, so 2mV/405uV is about 4.94 degrees above 25, or 29.94 deg C.
Can you send me your schematic? You need to have at least a 1uF cap between VREFOUT and VREFCOM, and VREFCOM should be tied to AVSS.
Thanks,
Bob B