This product has been released for a very long time so it is hard to get
information on it that is not in the datasheet. The PGA temperature drift is
not specified in the datasheet, however if temperature performance is really
important to the application, an external reference would be recommended.
We have some experiment results, dating from mid-October 1998, where an AD73360
internal reference with an absolute value of 1.25445 and positive/negative
tempco of -54.8/-110.9 ppm/C (operating in 3V mode with AVDD = 5V) was
overdriven by an AD780 external reference to produce a REFCAP absolute value of
2.49971 and positive/negative tempco of 1.0/1.5 ppm/C, over the temperature
range of -40C to +85C.