AD5764CSUZ datasheet(26/28 Pages) AD

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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

ADR425

±2

3.4

ADR02

±5

ADR395

±5

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