AD5644R datasheet(26/28 Pages) AD

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AD5624R/AD5644R/AD5664R

Data Sheet

Rev. D | Page 26 of 28

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 AD5624R/

AD5644R/AD5664R should have separate analog and digital

sections, each having its own area of the board. If the AD5624R/

AD5644R/AD5664R 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 AD5624R/AD5644R/AD5664R.

The power supply to the AD5624R/AD5644R/AD5664R 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 have 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 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 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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