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EVAL-AD7985FMCZ View Datasheet(PDF) - Analog Devices

Part Name
Description
MFG CO.
EVAL-AD7985FMCZ
ADI
Analog Devices ADI
'EVAL-AD7985FMCZ' PDF : 28 Pages View PDF
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Data Sheet
APPLICATIONS INFORMATION
LAYOUT
Design the printed circuit board (PCB) that houses the AD7985
so the analog and digital sections are separated and confined to
certain areas of the board. The pinout of the AD7985, with the
analog signals on the left side and the digital signals on the right
side, eases this task.
Avoid running digital lines under the device because they couple
noise onto the die, unless a ground plane under the AD7985 is
used as a shield. Fast switching signals, such as CNV or clocks,
must not run near analog signal paths. Crossover of digital and
analog signals must be avoided.
At least one ground plane must be used. It can be common or
split between the digital and analog sections. In the latter case,
the planes must be joined underneath the AD7985 devices.
The AD7985 voltage reference inputs (REF) have a dynamic
input impedance and must be decoupled with minimal parasitic
inductances. This is done by placing the reference decoupling
ceramic capacitor close to, ideally right against, the REF and
REFGND pins and connecting them with wide, low impedance
traces.
AD7985
Finally, the power supplies, VDD and VIO of the AD7985, must
be decoupled with ceramic capacitors, typically 100 nF, placed
close to the AD7985 and connected using short, wide traces to
provide low impedance paths and to reduce the effect of glitches
on the power supply lines.
EVALUATING THE AD7985 PERFORMANCE
Other recommended layouts for the AD7985 are outlined in
the documentation for the AD7985 evaluation board (EVAL-
AD7985FMCZ). 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-
SDP-CH1Z board.
Rev. C | Page 25 of 28
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