Datasheet

AD5764R Data Sheet
Rev. D | Page 28 of 32
APPLICATIONS INFORMATION
TYPICAL OPERATING CIRCUIT
Figure 43 shows the typical operating circuit for the AD5764R .
The only external components needed for this precision 16-bit
DAC are decoupling capacitors on the supply pins and reference
inputs, and an optional short-circuit current setting resistor.
Because the AD5764R incorporates a voltage reference and
reference buffers, it eliminates the need for an external bipolar
reference and associated buffers, resulting in an overall savings
in both cost and board space.
In Figure 43, AVDD is connected to +15 V, and AVSS is con-
nected to −15 V, but AV
DD
and AV
SS
can operate with supplies
from ±11.4 V to ±16.5 V. In Figure 43, AGNDx is connected to
REFGND.
Precision Voltage Reference Selection
To achieve the optimum performance from the AD5764R over
its full operating temperature range, an external voltage reference
must be used. Care must be taken in the selection of a precision
voltage reference. The AD5764R has two reference inputs,
REFAB and REFCD. The voltages applied to the reference inputs
are used to provide a buffered positive and negative reference
for the DAC cores. Therefore, any error in the voltage reference
is reflected in the outputs of the device.
There are four possible sources of error to consider when choosing
a voltage reference for high accuracy applications: initial accuracy,
temperature coefficient of the output voltage, long term drift,
and output voltage noise.
Initial accuracy error on the output voltage of an external refer-
ence could lead to a full-scale error in the DAC. Therefore, to
minimize these errors, a reference with low initial accuracy
error specification is preferred. Choosing a reference with an
output trim adjustment, such as the ADR425, allows a system
designer to trim system errors out by setting the reference
voltage to a voltage other than the nominal. The trim adjust-
ment can also be used at temperature to trim out any error.
Long-term drift is a measure of how much the reference output
voltage drifts over time. A reference with a tight long-term drift
specification ensures that the overall solution remains relatively
stable over its entire lifetime.
The temperature coefficient of a reference output voltage affects
INL, DNL, and TUE. A reference with a tight temperature coeffi-
cient specification should be chosen to reduce the dependence
of the DAC output voltage on ambient conditions.
In high accuracy applications, which have a relatively low noise
budget, reference output voltage noise must be considered. It is
important to choose a reference with as low an output noise
voltage as practical for the system resolution that is required.
Precision voltage references, such as the ADR435 (XFET® design),
produce low output noise in the 0.1 Hz to 10 Hz region. However,
as the circuit bandwidth increases, filtering the output of the
reference may be required to minimize the output noise.
Table 20. Some Precision References Recommended for Use with the AD5764R
Part No.
Initial Accuracy
(mV Maximum)
Long-Term Drift
(ppm Typical)
Temperature Drift
(ppm/°C Maximum)
0.1 Hz to 10 Hz Noise
(µV p-p Typical)
ADR435 ±6 30 3 3.5
ADR425 ±6 50 3 3.4
ADR02 ±5 50 3 10
ADR395 ±6 50 25 5
AD586 ±2.5 15 10 4