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AD7453

APPLICATION HINTS

Grounding and Layout

The printed circuit board that houses the AD7453 should be

designed so that the analog and digital sections are separated

and confined to certain areas of the board. This facilitates the

use of ground planes that can be easily separated. A minimum

etch technique is generally best for ground planes as it gives the

best shielding. Digital and analog ground planes should be

joined in only one place, and the connection should be a star

ground point established as close to the GND pin on the AD7453

as possible.

Avoid running digital lines under the device as this will couple

noise onto the die. The analog ground plane should be allowed

to run under the AD7453 to avoid noise coupling. The power

supply lines to the AD7453 should use as large a trace as pos-

sible to provide low impedance paths and reduce the effects of

glitches on the power supply line.

Fast switching signals like clocks should be shielded with digital

ground to avoid radiating noise to other sections of the board,

and clock signals should never run near the analog inputs.

Avoid crossover of digital and analog signals. Traces on oppo-

site sides of the board should run at right angles to each other.

This will reduce the effects of feedthrough through the board. A

microstrip technique is by far the best but is not always possible

with a double-sided board.

In this technique the component side of the board is dedicated

to ground planes while signals are placed on the solder side.

Good decoupling is also important. All analog supplies should

be decoupled with 10

mF tantalum capacitors in parallel with

0.1

mF capacitors to GND. To achieve the best from these

decoupling components, they must be placed as close as pos-

sible to the device.

EVALUATING THE AD7453 PERFORMANCE

The Evaluation Board Package includes a fully assembled and

tested evaluation board, documentation, and software for con-

trolling the board from a PC via the evaluation board controller.

The evaluation board controller can be used in conjunction with

the AD7453 evaluation board, as well as many other Analog

Devices evaluation boards ending with the CB designator, to

demonstrate/evaluate the ac and dc performance of the AD7453.

The software allows the user to perform ac (Fast Fourier Trans-

form) and dc (histogram of codes) tests on the AD7453. See the

evaluation board application note for more information.

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