i have notice in 10 different parts that VREF is 2.52v and not 2.4v that has
been written in the DataSheet .
what his the MAX or MIN of VREF in this chip ,would I consider this to a
problem in the chip.
The Vref is only specified as typical on the datasheet as it is not trimmed and
will vary from fab, lot to lot. The differential ADC architecture accommodates
variations in the Vref CM. The opinion of the AD6640 Applications Engineer is
that 2.52V is ok.