AD7451_15 Datasheet, PDF (23/25 Pages) Analog Devices – Pseudo Differential Input, 1 MSPS, 10-/12-Bit ADCs in an 8-Lead SOT-23

AD7441/AD7451
GROUNDING AND LAYOUT HINTS
The printed circuit board that houses the AD7441/AD7451
must be designed so that the analog and digital sections are
separated and confined to certain areas of the board. This
facilitates the use of ground planes that can be easily separated.
A minimum etch technique is generally best for ground planes,
as it gives the best shielding. Digital and analog ground planes
must be joined in only one place: a star ground point estab-
lished as close to the GND pin on the AD7441/AD7451 as
possible.
Avoid running digital lines under the device, as this couples
noise onto the die. The analog ground plane must be allowed to
run under the AD7441/AD7451 to avoid noise coupling. The
power supply lines to the AD7441/AD7451 must use as large
a trace as possible to provide low impedance paths and reduce
the effects of glitches on the power supply line.
Fast switching signals like clocks must be shielded with digital
grounds to avoid radiating noise to other sections of the board,
and clock signals must never run near the analog inputs. Avoid
crossover of digital and analog signals. Traces on opposite sides
of the board must run at right angles to each other. This reduces
the effects of feedthrough on the board. A microstrip technique is
by far the best but is not always possible with a double-sided board.
In this technique, the component side of the board is dedicated
to ground planes while signals are placed on the solder side.
Good decoupling is also important. All analog supplies must
be decoupled with 10 μF tantalum capacitors in parallel with
0.1 μF capacitors to GND. To achieve the best from these
decoupling components, they must be placed as close as
possible to the device.
EVALUATING PERFORMANCE
The evaluation board package includes a fully assembled and
tested evaluation board, documentation, and software for con-
trolling the board from a PC via the evaluation board controller.
The evaluation board controller can be used in conjunction with
the AD7441 and the AD7451 evaluation boards, as well as with
many other Analog Devices, Inc. evaluation boards ending with
the CB designator, to demonstrate and evaluate the ac and dc
performance of the AD7441 and the AD7451.
The software allows the user to perform ac (fast Fourier transform)
and dc (histogram of codes) tests on the AD7441/AD7451. See
the AD7441/AD7451 application note that accompanies the
evaluation kit for more information.
Rev. D | Page 22 of 24