Datasheet

AD5764 Data Sheet
Rev. F | Page 26 of 28
Precision Voltage Reference Selection
To achieve the optimum performance from the AD5764 over its
full operating temperature range, a precision voltage reference
must be used. Consideration should be given to the selection of
a precision voltage reference. The AD5764 has two reference
inputs, REFAB and REFCD. The voltages applied to the refer-
ence 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 can 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. Choose a reference with a tight temperature
coefficient specification 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 needs to be considered.
Choosing a reference with as low an output noise voltage as
practical for the system resolution required is important. 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 AD5764
Part No. Initial Accuracy (mV Max) Long-Term Drift (ppm Typ) Temp Drift (ppm/°C Max) 0.1 Hz to 10 Hz Noise (μV p-p Typ)
ADR435 ±2 40 3 8
ADR425 ±2 50 3 3.4
ADR02 ±5 50 3 10
ADR395 ±5 50 9 8