AD5624/AD5664

Rev. 0 | Page 21 of 24

BIPOLAR OPERATION USING THE

AD5624/AD5664

The AD5624/AD5664 have been designed for single-supply

operation, but a bipolar output range is also possible using the

circuit in Figure 40. The circuit gives 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:

⎥

⎦

⎤

⎢

⎣

⎡

⎟

⎠

⎞

⎜

⎝

⎛

×

−

⎟

⎠

⎞

⎜

⎝

⎛

+

×

⎟

⎠

⎞

⎜

⎝

⎛

×

=

R1

R2

V

R1

R2

R1

D

V

V

DD

DD

O

536

,

65

where D represents the input code in decimal (0 to 65536).

V

5

536

,

65

10

−

⎟

⎠

⎞

⎜

⎝

⎛

×

=

D

This is an output voltage range of ±5 V, with 0x0000 corre-

sponding to a −5 V output, and 0xFFFF corresponding to a

+5 V output.

3-WIRE

SERIAL

INTERFACE

R2 = 10kΩ

+5V

–5V

AD820/

OP295

+5V

AD5624/

AD5664

R1 = 10kΩ

±5V

0.1µF

10µF

Figure 40. Bipolar Operation with the AD5624/AD5664

USING AD5624/AD5664 WITH A

GALVANICALLY ISOLATED INTERFACE

In process control applications in industrial environments, it is

often necessary to use a galvanically isolated interface to protect

and isolate the controlling circuitry from any hazardous

common-mode voltages that might occur in the area where the

DAC is functioning. Isocouplers provide isolation in excess of

3 kV. The AD5624/AD5664 use a 3-wire serial logic interface,

so the ADuM130x 3-channel digital isolator provides the

required isolation (see Figure 41). The power supply to the part

also needs to be isolated, which 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 AD5624/AD5664.

0.1µF

5V

REGULATOR

GND

DIN

SYNC

SCLK

POWER

10µF

SDI

SCLK

DATA

AD5624/

AD5664

VOB

VOA

VOC

V1C

V1B

V1A

ADuM1300

Figure 41. AD5624/AD5664 with a Galvanically Isolated Interface

POWER SUPPLY BYPASSING AND GROUNDING

When accuracy is important in a circuit, it is helpful to consider

carefully the power supply and ground return layout on the

board. The printed circuit board containing the AD5624/

AD5664 should have separate analog and digital sections, each

having its own area of the board. If the AD5624/AD5664 is in a

system where other devices require an AGND-to-DGND

connection, the connection should be made at one point only.

This ground point should be as close as possible to the

AD5624/AD5664.

The power supply to the AD5624/AD5664 should be bypassed

with 10 μF and 0.1 μF capacitors. The capacitors should be

located as close as possible to the device, with the 0.1 μF capacitor

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

tantalum bead type. It is important that the 0.1 μF capacitor has

low effective series resistance (ESR) and effective series

inductance (ESI), for example, 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

possible to provide a low impedance path and to 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 2-layer board.