AD7366/AD7367
APPLICATION HINTS
To avoid radiating noise to other sections of the board, com-
ponents, such as clocks, with fast switching signals should be
shielded with digital ground and should never be run near the
analog inputs. Avoid crossover of digital and analog signals. To
reduce the effects of feedthrough within the board, traces should
be run at right angles to each other. A microstrip technique is
the best method, but its use may not be possible with a double-
sided board. In this technique, the component side of the board
is dedicated to ground planes, and signals are placed on the
other side.
LAYOUT AND GROUNDING
The printed circuit board that houses the AD7366/AD7367
should be designed so that the analog and digital sections are
confined to their own separate areas of the board. This design
facilitates the use of ground planes that can be easily separated.
To provide optimum shielding for ground planes, a minimum
etch technique is generally the best option. All AGND pins on
the AD7366/AD7367 should be connected to the AGND plane.
Digital and analog ground pins should be joined in only one
place. If the AD7366/AD7367 are in a system where multiple
devices require an AGND and DGND connection, the connec-
tion should still be made at only one point. A star point should
be established as close as possible to the ground pins on the
AD7366/AD7367.
Good decoupling is also important. All analog supplies should
be decoupled with 1ꢀ ꢃF tantalum capacitors in parallel with
ꢀ.1 ꢃF capacitors to AGND. To achieve the best results from
these decoupling components, they must be placed as close as
possible to the device, ideally right up against the device. The
ꢀ.1 ꢃF capacitors should have a low effective series resistance
(ESR) and low effective series inductance (ESI), such as is typical
of common ceramic and surface mount types of capacitors. These
low ESR, low ESI capacitors provide a low impedance path to
ground at high frequencies to handle transient currents due to
internal logic switching.
Good connections should be made to the power and ground
planes. This can be done with a single via or multiple vias for
each supply and ground pin.
Avoid running digital lines under the AD7366/AD7367 devices
because this couples noise onto the die. However, the analog
ground plane should be allowed to run under the AD7366/
AD7367 to avoid noise coupling. The power supply lines to
the AD7366/AD7367 should use as large a trace as possible to
provide low impedance paths and reduce the effects of glitches
on the power supply line.
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