AD5744R datasheet(27/32 Pages) AD

27 / 32 page

AD5744R

Rev. A | Page 27 of 32

APPLICATIONS INFORMATION

TYPICAL OPERATING CIRCUIT

Figure 43 shows the typical operating circuit for the AD5744R.

The only external components needed for this precision 14-bit

DAC are decoupling capacitors on the supply pins and reference

inputs and an optional short-circuit current setting resistor.

Because the AD5744R 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 connected

to −15 V; but AVDD and AVSS 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 AD5744R 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 AD5744R 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 adjustment

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 coef-

ficient 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 18. Some Precision References Recommended for Use with the AD5744R

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

3.5

ADR425

±6

3.4

ADR02

±5

ADR395

±6

AD586

±2.5

AD5744R Datasheet(PDF) 27 Page - Analog Devices

AD5744R Datasheet(HTML) 27 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL