Data Sheet

AD5624/AD5664

Rev. A | Page 21 of 23

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 41. 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

R1

R2

R1

536

,

65

DD

DD

O

V

D

V

V

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 = 10k

Ω

+5V

–5V

AD820/

OP295

+5V

AD5624/

AD5664

R1 = 10k

Ω

±5V

0.1µF

10µF

Figure 41. 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 42). The power supply to the device 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 42. 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

has 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, make the

connection at one point only. This ground point must be as

close as possible to the AD5624/AD5664.

The power supply to the AD5624/AD5664 must be bypassed with

10 µF and 0.1 µF capacitors. The capacitors must 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 has 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

must 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 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. This is not always possible with a 2-layer board.