ADR435 datasheet(29/33 Pages) AD

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Preliminary Technical Data

AD5762R

Rev. PrA | Page 29 of 33

APPLICATIONS INFORMATION

TYPICAL OPERATING CIRCUIT

Figure 42 shows the typical operating circuit for the AD5762R.

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 AD5762R incorporates a voltage reference and

reference buffers, it eliminates the need for an external bipolar

reference and associated buffers. This leads to an overall savings

in both cost and board space.

In Figure 42, VDD and VSS are both connected to ±15 V, but VDD

and VSS can operate with supplies from ±11.4 V to ±16.5 V. In

Figure 42, AGNDA and AGNDB are connected to REFGND.

10 11 12 13 14 15 16

32 31 30 29 28 27 26 25

AD5762R

SYNC

SCLK

SDIN

SDO

LDAC

CLR

VOUTA

AGNDA

VOUTB

AGNDB

SYNC

SCLK

SDIN

SDO

LDAC

RSTOUT

RSTIN

BIN/2sCOMP

+5V

+15V –15V

VOUTB

VOUTA

100nF

10µF

100nF

10µF

TEMP

10µF

Figure 42. Typical Operating Circuit

Precision Voltage Reference Selection

To achieve the optimum performance from the AD5762R over

its full operating temperature range, an external voltage

reference must be used. Thought should be given to the

selection of a precision voltage reference. The voltage applied to

the reference input is 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 ad-

justment 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’s output voltage

affects INL, DNL, and TUE. A reference with a tight

temperature coefficient 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 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 18. Some Precision References Recommended for Use with the AD5762R

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

±6

3.4

ADR425

±6

3.4

ADR02

±5

ADR395

±6

AD586

±2.5

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