Datasheet

AD5680
Rev. A | Page 15 of 20
CHOOSING A REFERENCE FOR THE AD5680
To achieve the optimum performance from the AD5680, choose
a precision voltage reference carefully. The AD5680 has only
one reference input, V
REF
. The voltage on the reference input is
used to supply the positive input to the DAC. Therefore, any
error in the reference is reflected in the DAC.
When choosing a voltage reference for high accuracy applica-
tions, the sources of error are initial accuracy, ppm drift, long-
term drift, and output voltage noise. Initial accuracy on the
output voltage of the DAC leads to a full-scale error in the DAC.
To minimize these errors, a reference with high initial accuracy
is preferred. In addition, choosing a reference with an output
trim adjustment, such as the
ADR425, allows a system designer
to trim out system errors by setting a reference voltage to a
voltage other than the nominal. The trim adjustment can also
be used at temperature to trim out any error.
Long-term drift is a measurement of how much the reference
drifts over time. A reference with a tight long-term drift speci-
fication ensures that the overall solution remains relatively stable
during its entire lifetime.
The temperature coefficient of a reference’s output voltage
affects INL, DNL, and TUE. A reference with a tight temperature
coefficient specification should be chosen to reduce temperature
dependence of the DAC output voltage in ambient conditions.
In high accuracy applications, which have a relatively low noise
budget, reference output voltage noise needs to be considered. It
is important to choose a reference with as low an output noise
voltage as is practical for the system noise resolution required.
Precision voltage references such as the
ADR425 produce low
output noise in the 0.1 Hz to 10 Hz range. Examples of recom-
mended precision references for use as supply to the AD5680
are shown in the
Table 6.
Table 6. Partial List of Precision References for Use with the AD5680
Part No. Initial Accuracy (mV max) Temperature Drift (ppm/°C max) 0.1 Hz to 10 Hz Noise (μV p-p typ) V
OUT
(V)
ADR425 ±2 3 3.4 5
ADR395 ±6 25 5 5
REF195 ±2 5 50 5