Data Sheet

AD5601/AD5611/AD5621

Rev. G | Page 19 of 24

USING THE AD5601/AD5611/AD5621 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. iCoupler® provides isolation in excess of

2.5 kV. Because the AD5601/AD5611/AD5621 use a 3-wire serial

logic interface, the ADuM1300 3-channel digital isolator

provides the required isolation (see Figure 53). 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 AD5601/

AD5611/AD5621.

Figure 53. AD5601/AD5611/AD5621 with a Galvanically 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 PCB containing the AD5601/AD5611/AD5621

should have separate analog and digital sections, each having its

own area of the board. If the AD5601/AD5611/AD5621 are 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

AD5601/AD5611/AD5621.

The power supply to the AD5601/AD5611/AD5621 should be

bypassed with 10 µF and 0.1 µF capacitors. The capacitors

should be physically 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 have low effective series resistance (ESR) and

effective series inductance (ESI), such as in common ceramic

types of capacitors. This 0.1 µF capacitor provides a low imped-

ance 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 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 on the board. The best board layout tech-

nique 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.

AD5601/

AD5611/

AD5621

ADuM1300

POWER

10µF

0.1µF

GND

5V

REGULATOR

SCLK

SYNC

SCLK

SDI

DATA

SDIN