AD5320

–11–

REV. B

Bipolar Operation Using the AD5320

The AD5320 has been designed for single-supply operation but

a bipolar output range is also possible using the circuit in Figure

30. The circuit below will give an output voltage range of

±5 V.

Rail-to-rail operation at the amplifier output is achievable using

an AD820 or an OP295 as the output amplifier.

The output voltage for any input code can be calculated as

follows:

D

4096









×

R1

+ R2

R1









R2

R1

























where D represents the input code in decimal (0–4095).

Ω:

V

10

× D

4096









–5 V

This is an output voltage range of

±5 V with 000 Hex corre-

sponding to a –5 V output and FFF Hex corresponding to a

+5 V output.

THREE-WIRE

SERIAL

INTERFACE

+5V

AD5320

10 F

0.1 F

R1 = 10k

R2 = 10k

+5V

5V

–5V

AD820/

OP295

Figure 30. Bipolar Operation with the AD5320

Using AD5320 with an Opto-Isolated Interface

In process-control applications in industrial environments it is

often necessary to use an opto-isolated interface to protect and

isolate the controlling circuitry from any hazardous common-

mode voltages that may occur in the area where the DAC is

functioning. Opto-isolators provide isolation in excess of 3 kV.

Because the AD5320 uses a three-wire serial logic interface, it

requires only three opto-isolators to provide the required isola-

tion (see Figure 31). The power supply to the part also needs to

be isolated. This is done by using a transformer. On the DAC

side of the transformer, a +5 V regulator provides the +5 V

supply required for the AD5320.

0.1 F

10k

10k

10k

+5V

REGULATOR

GND

DIN

SYNC

SCLK

POWER

10 F

SYNC

SCLK

DATA

AD5320

Figure 31. AD5320 with An Opto-Isolated Interface

Power Supply Bypassing and Grounding

When accuracy is important in a circuit it is helpful to carefully

consider the power supply and ground return layout on the

board. The printed circuit board containing the AD5320 should

have separate analog and digital sections, each having its own

area of the board. If the AD5320 is in a system where other

devices require an AGND to DGND connection, the connec-

tion should be made at one point only. This ground point

should be as close as possible to the AD5320.

The power supply to the AD5320 should be bypassed with

10

µF and 0.1 µF capacitors. The capacitors should be physi-

cally as close as possible to the device with the 0.1

µF capacitor

ideally right up against the device. The 10

µF capacitors are the

tantalum bead type. It is important that the 0.1

µF capacitor has

low Effective Series Resistance (ESR) and Effective Series In-

ductance (ESI), e.g., common ceramic types of capacitors. This

0.1

µF capacitor provides a low impedance path to ground for

high frequencies caused by transient currents due to internal

logic switching.

The power supply line itself should have as large a trace as pos-

sible to provide a low impedance path and reduce glitch effects

on the supply line. Clocks and other fast switching digital signals

should be shielded from other parts of the board by digital

ground. Avoid crossover of digital and analog signals if possible.

When traces cross on opposite sides of the board, ensure that

they run at right angles to each other to reduce feedthrough

effects through the board. The best board layout technique is

the microstrip technique where the component side of the board

is dedicated to the ground plane only and the signal traces are

placed on the solder side. However, this is not always possible

with a two-layer board.