AD5662ARM datasheet(17/20 Pages) AD

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Preliminary Technical Data

AD5662

Rev. PrA | Page 17 of 20

USING AD5662 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 may occur in the area where the

DAC is functioning. Isocouplers provide isolation in excess of

3 kV. The AD5662 uses a 3-wire serial logic interface so the

ADuM130x 3-channel digital isolator provides the required

isolation (see Figure 38). 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 AD5662.

VDD

0.1

µF

VDD

10k

Ω

10k

Ω

VDD

10k

Ω

+5V

REGULATOR

VOUT

GND

DIN

SYNC

SCLK

POWER

µF

SYNC

SCLK

DATA

AD5662

Figure 38. AD5662 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 AD5662 should

have separate analog and digital sections, each having its own

area of the board. If the AD5662 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 AD5662.

The power supply to the AD5662 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 capacitors are 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 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.

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