@3,3V operating voltage.
Referred to the datasheet (Rev D, page 4) the internal reference voltage is
specified at 1,235V (typ) and no min/max value is stated there.
Because we’ve detected that the voltage is varied from the typical value I ask
you what the variation of the internal reference voltage actually is.
There is a mistake in the datasheet.
I have a printout of the original datasheet and this shows the following for
both 3.3V and 5V:
min typ max
Vref Internal: 1.12 1.235 1.35
Vref External: 1.14 1.235 1.26
So internal tolerances show the min and max that can be generated, whereas
external tolerances show min and max that should be applied.
External Vref is strongly recommended for better performance especially at
higher speeds. When
using the internal reference the VREF pin needs to be tied to VAA via a 0.1uF