AD7785 datasheet(28/32 Pages) AD

28 / 32 page

AD7785

Rev. 0 | Page 28 of 32

The ground planes of the AD7785 should be allowed to run

under the device to prevent noise coupling. The power supply

lines to the AD7785 should use as wide a trace as possible to

provide low impedance paths and reduce the effects of glitches

on the power supply line. Fast switching signals such as clocks

should be shielded with digital ground to avoid radiating noise

to other sections of the board, and clock signals should never be

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 reduces the effects of feedthrough through the board.

A microstrip technique is by far the best, but it is not always

possible with a double-sided board. In this technique, the

component side of the board is dedicated to ground planes, and

signals are placed on the solder side.

Good decoupling is important when using high resolution

ADCs. AVDD should be decoupled with 10 μF tantalum in

parallel with 0.1 μF capacitors to GND. DVDD should be

decoupled with 10 μF tantalum in parallel with 0.1 μF

capacitors to the system’s DGND plane, with the system’s

AGND to DGND connection being close to the AD7785.

To achieve the best from these decoupling components, they

should be placed as close as possible to the device, ideally right

up against the device. All logic chips should be decoupled with

0.1 μF ceramic capacitors to DGND.

AD7785 Datasheet(PDF) 28 Page - Analog Devices