ADS54J60: dc-coupled common mode voltage

Part Number: ADS54J60

Tool/software:

Dear Sirs,

In ADS54J60 datasheet, it specifes an internal voltage of 2.1V added as common mode voltage. I wonder if I can turn off this internal CMN voltage and use external one----dc-coupled signal applied to INAM & INAP.

INAP=dc bias_1 +gain* Vin; INAM=dc bias_2 - gain*Vin

CMN=(dc bias_1 + dc bias_2)/2

Anthother question is if I can set the CMN as half of 1.9V, which is equal to 0.95V. Can you let me know why the internal CMN voltage is set as 2.1V, normally the CMN should be half of the Vref voltage.

BTW, I cannot find VREF voltage of this ADC. why?

The question is a bit urgent, could you help to answer me by today?

Thanks a lot

John