AD7356 datasheet(20/21 Pages) AD

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Data Sheet

AD7356

Rev. B | Page 19 of 20

APPLICATION HINTS

GROUNDING AND LAYOUT

The analog and digital supplies to the AD7356 are independent

and separately pinned out to minimize coupling between the

analog and digital sections of the device. Design the printed

circuit board (PCB)that houses the AD7356 so that the analog

and digital sections are separated and confined to certain areas

of the board. This design facilitates the use of ground planes

that can be easily separated.

To provideoptimumshieldingfor groundplanes, a minimumetch

technique is generally best. Sinkthe two AGND pins of the

AD7356 in the AGND plane, and sinkthe REFGND pin in the

AGND plane. Digital and analog groundplanesmust bejoined

in only one place.If theAD7356is in a systemin which multiple

devices requirean AGNDandDGNDconnection,theconnection

must still be made at one point only, a star ground point that

must be established as close as possibleto the groundpins on

the AD7356.

Avoid running digital lines underthedevicebecausethis couples

noise onto the die. Allow the analog groundplanesto run under

the AD7356 to avoid noise coupling. The power supply lines to

the AD7356 should useaslargea traceas possible to providelow

impedance paths and reducethe effects of glitches on the power

supply line.

To avoid radiating noise to other sectionsof the board, shield

fast switching signals such as clocks, with digital ground; and

never runclocksignalsneartheanalog inputs. Avoidcrossoverof

digital and analog signals. To reduce the effects of feedthrough

within the board, traces on opposite sidesof the board should

run at right angles to each other. A microstrip techniqueis the

best methodbutis notalways possiblewitha double sided board.

In this technique, the component side of the boardis dedicated

to ground planes and signals are placedon the solderside.

Good decoupling is important; decouple all supplieswith 10 µF

tantalum capacitors in parallel with 0.1 µF capacitors to GND.

To achievethebest resultsfromthesedecoupling components,

they must be placed as close as possibleto the device, ideally

right up against the device. The 0.1 µF capacitor, (including the

common ceramictypes or surface-mounttypes)should havelow

effective series resistance (ESR)and effective seriesinductance

(ESI). These lowESR and ESIcapacitors providea lowimpedance

path to ground at high frequencies to handle transient currents

due to logic switching.

EVALUATING THE AD7356 PERFORMANCE

The recommendedlayout for the AD7356 is outlined in the

EVAL-AD7356EDZ documentation. The EVAL-AD7356EDZ

package includes a fully assembled andtested evaluation board,

documentation, andsoftwarefor controlling the board fromthe

PC via the converterevaluation anddevelopment board (CED).

The CED canbeused in conjunction with theEVAL-AD7356EDZ

(as well as many other evaluationboards ending in the ED

designatorfromAnalog Devices, Inc.)todemonstrate/evaluatethe

ac and dc performance of the AD7356.

The softwareallowstheusertoperformac(fast Fouriertransform)

and dc (linearity) tests on the AD7356. The software and

documentationareon a CDshippedwiththeEVAL-AD7356EDZ.

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