AD5752 datasheet(28/32 Pages) AD

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AD5722/AD5732/AD5752

Rev. 0 | Page 28 of 32

APPLICATIONS INFORMATION

+5 V/±5 V OPERATION

When operating from a single +5 V supply or a dual ±5 V supply,

an output range of +5 V or ±5 V is not achievable because suffi-

cient headroom for the output amplifier is not available. In this

situation, a reduced reference voltage can be used. For example,

a 2 V reference voltage produces an output range of +4 V or ±4 V,

and the 1 V of headroom is more than enough for full operation.

A standard value voltage reference of 2.048 V can be used to

produce output ranges of +4.096 V and ±4.096 V.

LAYOUT GUIDELINES

In any circuit where accuracy is important, careful consideration

of the power supply and ground return layout helps to ensure

the rated performance. The printed circuit board on which the

AD5722/AD5732/AD5752 are mounted should be designed so

that the analog and digital sections are separated and confined

to certain areas of the board. If the AD5722/AD5732/AD5752

are in a system where multiple devices require an AGND-to-

DGND connection, the connection should be made at one

point only. The star ground point should be established as close

as possible to the device.

The AD5722/AD5732/AD5752 should have ample supply bypass-

ing of a 10 µF capacitor in parallel with a 0.1 µF capacitor on

each supply located as close to the package as possible, ideally

right up against the device. The 10 µF capacitor is the tantalum

bead type. The 0.1 µF capacitor should have low effective series

resistance (ESR) and low effective series inductance (ESI) such

as the common ceramic types, which provide a low impedance

path to ground at high frequencies to handle transient currents

due to internal logic switching.

The power supply lines of the AD5722/AD5732/AD5752 should

use as large a trace as possible to provide low impedance paths

and reduce the effects of glitches on the power supply line. Fast

switching signals, such as a data clock, should be shielded with

digital ground to avoid radiating noise to other parts of the

board, and they should never be run near the reference inputs.

A ground line routed between the SDIN and SCLK lines helps

reduce crosstalk between them (this is not required on a

multilayer board that has a separate ground plane, but separating

the lines does help). It is essential to minimize noise on the

REFIN line because any unwanted signals can couple through

to the DAC outputs.

Avoid crossover of digital and analog signals. Traces on

opposite sides of the board should run at right angles to each

other. This reduces the effects of feedthrough on the board. A

microstrip technique is by far the best method, but it is not

always possible with a double-sided board. In this technique,

the component side of the board is dedicated to a ground plane,

and signal traces are placed on the solder side.

GALVANICALLY ISOLATED INTERFACE

In many process control applications, it is necessary to provide

an isolation barrier between the controller and the unit being

controlled to protect and isolate the controlling circuitry from

any hazardous common-mode voltages that may occur. The

iCoupler® family of products from Analog Devices, Inc., provides

voltage isolation in excess of 2.5 kV. The serial loading structure

of the AD5722/AD5732/AD5752 makes them ideal for isolated

interfaces because the number of interface lines is kept to a

minimum. Figure 43 shows a 4-channel isolated interface to the

AD5722/AD5732/AD5752 using an ADuM1400. For further

information, visit http://www.analog.com/icouplers.

ENCODE

DECODE

ENCODE

DECODE

ENCODE

DECODE

VIA

VIB

VIC

VID

VOA

VOB

VOC

VOD

ENCODE

DECODE

ADuM1400*

MICROCONTROLLER

SERIAL CLOCK OUT

SERIAL DATA OUT

SYNC OUT

CONTROL OUT

TO SCLK

TO SDIN

TO SYNC

TO LDAC

*ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 43. Isolated Interface

VOLTAGE REFERENCE SELECTION

To achieve optimum performance from the AD5722/AD5732/

AD5752 over their full operating temperature range, a precision

voltage reference must be used. Thought should be given to the

selection of a precision voltage reference. The voltage applied to

the reference inputs 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

reference can lead to a full-scale error in the DAC. 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 ADR421, allows a

system designer to trim out system errors by setting the

reference voltage to a voltage other than the nominal. The

trim adjustment can also be used to trim out temperature-

induced errors.

•

The temperature coefficient of a reference 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.

•

Long-term drift is a measure of how much the reference

output voltage drifts over time. A reference with a tight

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