AD7940 datasheet(23/24 Pages) AD

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Preliminary Technical Data

AD7693

Rev. PrB | Page 23 of 24

APPLICATION HINTS

LAYOUT

The printed circuit board that houses the AD7693 should be

designed so that the analog and digital sections are separated

and confined to certain areas of the board. The pinout of the

AD7693, with all its analog signals on the left side and all its

digital signals on the right side, eases this task.

Avoid running digital lines under the device because these

couple noise onto the die unless a ground plane under the

AD7693 is used as a shield. Fast switching signals, such as CNV

or clocks, should not run near analog signal paths. Crossover of

digital and analog signals should be avoided.

At least one ground plane should be used. It could be common

or split between the digital and analog sections. In the latter

case, the planes should be joined underneath the AD7693s.

Figure 45. Example Layout of the AD7693 (Top Layer)

The AD7693 voltage reference input REF has a dynamic input

impedance and should be decoupled with minimal parasitic

inductances. This is done by placing the reference decoupling

ceramic capacitor close to, ideally right up against, the REF and

GND pins and connecting them with wide, low impedance traces.

Finally, the power supplies VDD and VIO of the AD7693

should be decoupled with ceramic capacitors, typically 100 nF,

placed close to the AD7693 and connected using short and wide

traces to provide low impedance paths and reduce the effect of

glitches on the power supply lines.

An example of a layout following these rules is shown in

Figure 45 and Figure 46.

EVALUATING THE AD7693’S PERFORMANCE

Figure 46. Example Layout of the AD7693 (Bottom Layer)

Other recommended layouts for the AD7693 are outlined

in the documentation of the evaluation board for the AD7693

(EVAL-AD7693-CB). The evaluation board package includes

a fully assembled and tested evaluation board, documentation,

and software for controlling the board from a PC via the

EVAL-CONTROL BRD3.

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