Datasheet

AD7294 Data Sheet
Rev. H | Page 26 of 48
The AD7294 can also operate with an external reference.
Suitable reference sources for the AD7294 include AD780,
AD1582, ADR431, REF193, and ADR391. In addition, choosing
a reference with an output trim adjustment, such as the ADR441,
allows a system designer to trim system errors by setting a
reference voltage to a voltage other than the nominal.
Long-term drift is a measure of how much the reference drifts
over time. A reference with a low long-term drift specification
ensures that the overall solution remains stable during its entire
lifetime. If an external reference is used, select a low temperature
coefficient specification to reduce the temperature dependence
of the system output voltage on ambient conditions.
V
DRIVE
FEATURE
The AD7294 also has a V
DRIVE
feature to control the voltage at
which the I
2
C interface operates. The V
DRIVE
pin is connected to
the supply to which the I
2
C bus is pulled. This pin sets the input
and output threshold levels for the digital logic pins and the
I
SENSE
OVERRANGE pins. The V
DRIVE
feature allows the AD7294
to easily interface to both 3 V and 5 V processors. For example,
if the AD7294 is operated with a V
DD
of 5 V, t h e V
DRIVE
pin can
be powered from a 3 V supply, allowing a large dynamic range
with low voltage digital processors. Thus, the AD7294 can be
used with the 2 × V
REF
input range with a V
DD
of 5 V, yet remains
capable of interfacing to 3 V digital parts. Decouple this pin to
DGND with a 100 nF and a 1 μF capacitor.