ADA4841-X AD [Analog Devices], ADA4841-X Datasheet - Page 19

• Manufacturer Part Number: ADA4841-X
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
AD7689
APPLICATION HINTS
LAYOUT
Figure 21. Example Layout of the AD7689 (Top Layer)
The printed circuit board that houses the AD7689 should be
designed so that the analog and digital sections are separated
Figure 22. Example Layout of the AD7689 (Bottom Layer)
and confined to certain areas of the board. The pinout of the
AD7689, 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
AD7689 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 AD7689s.
The AD7689 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 AD7689
should be decoupled with ceramic capacitors, typically 100 nF,
placed close to the AD7689 and connected using short, 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 21 and Figure 22.
EVALUATING AD7689 PERFORMANCE
Other recommended layouts for the AD7689 are outlined
in the documentation of the evaluation board for the AD7689
(EVAL-AD7689CBZ). 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
BRD3Z.
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