AD5643R datasheet(28/32 Pages) AD

28 / 32 page

AD5623R/AD5643R/AD5663R

Data Sheet

Rev. G | Page 28 of 32

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 AD5663R

should have separate analog and digital sections, each having its

own area of the board.

If the AD5663R 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 AD5663R.

The power supply to the AD5663R 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 have low

effective series resistance (ESR) and effective series inductance

(ESI), which is found, for example, in 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.

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