AD7680 datasheet(23/28 Pages) AD

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AD7688

Rev. A | Page 23 of 28

APPLICATION HINTS

LAYOUT

The printed circuit board that houses the AD7688 should be

designed so that the analog and digital sections are separated

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

AD7688, 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

AD7688 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 sections. In the latter

case, the planes should be joined underneath the AD7688s.

The AD7688 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 connecting it with wide, low impedance

traces.

Finally, the power supplies VDD and VIO of the AD7688

should be decoupled with ceramic capacitors (typically 100 nF)

placed close to the AD7688 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 46 and Figure 47.

EVALUATING THE AD7688’S PERFORMANCE

Other recommended layouts for the AD7688 are outlined

in the documentation of the evaluation board for the AD7688

(EVAL-AD7688). 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.

Figure 46. Example of Layout of the AD7688 (Top Layer)

Figure 47. Example of Layout of the AD7688 (Bottom Layer)

AD7680 Datasheet(PDF) 23 Page - Analog Devices