AD7450ARM datasheet(23/24 Pages) AD

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REV. PrJ

PRELIMINARY TECHNICAL DATA

–23–

AD7450

APPLICATION HINTS

Grounding and Layout

The printed circuit board that houses the AD7450 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 sepa-

rated.

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 estab-

lished as close to the GND pin on the AD7450 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 AD7450 to

avoid noise coupling.

The power supply lines to the

AD7450 should use as large a trace as possible 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 sig-

nals.

Traces on opposite 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 dedi-

cated to ground planes while signals are placed on the

solder side.

Good decoupling is also important.

All analog supplies

should be decoupled with 10µF tantalum capacitors in

parallel with 0.1µF capacitors to GND.

To achieve the

best from these decoupling components, they must be

placed as close as possible to the device.

EVALUATING THE AD7450 PERFORMANCE

The recommended layout for the AD7450 is outlined in

the evaluation board for the AD7450.

The evaluation

board package includes a fully assembled and tested evalu-

ation board, documentation and software for controlling

the board from a PC via the EVALUATION BOARD

CONTROLLER.

The EVALUATION BOARD CON-

TROLLER can be used in conjunction with the AD7450

evaluation board, as well as many other Analog Devices’

evaluation boards ending with the CB designator, to dem-

onstrate/evaluate the ac and dc performance of the

AD7450.

The software allows the user the perform ac (fast Fourier

Transform) and dc (Histogram of codes) tests on the

AD7450.

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