AD7980 datasheet(20/22 Pages) AD

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AD7980

Preliminary Technical Data

Rev Pr C | Page 20 of 22

APPLICATION HINTS

LAYOUT

The printed circuit board that houses the AD7980 should be

designed so that the analog and digital sections are separated

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

AD7980, 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

AD7980 is used as a shield. Fast switching signals, such as CNV

or clocks, should never 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 section. In the latter case,

the planes should be joined underneath the AD7980s.

The AD7980 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, and ideally right up against, the REF

and GND pins and connected with wide, low impedance traces.

Finally, the power supplies VDD and VIO of the AD7980

should be decoupled with ceramic capacitors, typically 100 nF,

placed close to the AD7980 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 layout following these rules is shown in

Figure 27 and Figure 28.

EVALUATING THE AD7980’S PERFORMANCE

Other recommended layouts for the AD7980 are outlined

in the documentation of the evaluation board for the AD7980

(EVAL-AD7980-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.

AD7980

Figure 27. Example of Layout of the AD7980 (Top Layer)

Figure 28. Example of Layout of the AD7980 (Bottom Layer)

AD7980 Datasheet(PDF) 20 Page - Analog Devices