AD7466/AD7467/AD7468
Rev. C | Page 25 of 28
APPLICATION HINTS
GROUNDING AND LAYOUT
The printed circuit board that houses the AD7466/AD7467/
AD7468 should be designed such that the analog and digital
sections are separated and confined to certain areas. This facili-
tates the use of ground planes that can be separated easily. A
minimum etch technique is generally best for ground planes
because it gives the best shielding. Digital and analog ground
planes should be joined at only one place. If the devices are in a
system where multiple devices require an AGND to DGND
connection, the connection should still be made at one point
only, a star ground point, which should be established as close
as possible to the AD7466/AD7467/AD7468.
Avoid running digital lines under the device because these
couple noise onto the die. The analog ground plane should be
allowed to run under the AD7466/AD7467/AD7468 to avoid
noise coupling. The power supply lines to the devices should
use as large a trace as possible to provide low impedance paths
and to reduce the effects of glitches on the power-supply line.
Fast switching signals, like clocks, should be shielded with
digital ground to avoid radiating noise to other sections of the
board, and clock signals should never be run near the analog
inputs. Avoid crossover of digital and analog signals. Traces on
opposite sides of the board should run at right angles to each
other to reduce the effects of feedthrough on the board. A
microstrip technique is the best choice, but is not always
possible with a double-sided board. With 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 very important. All analog supplies
should be decoupled with 10 μF tantalum in parallel with 0.1 μF
capacitors to AGND. All digital supplies should have a 0.1 μF
ceramic disc capacitor to DGND. To achieve the best perform-
ance from these decoupling components, the user should keep
the distance between the decoupling capacitor and the V
DD
and
GND pins to a minimum, with short track lengths connecting
the respective pins.
EVALUATING THE PERFORMANCE
OF THE AD7466 AND AD7467
The evaluation board package includes a fully assembled and
tested evaluation board, documentation, and software for
controlling the board from the PC via an evaluation board
controller. To evaluate the ac and dc performance of the
AD7466 and AD7467, the evaluation board controller can be
used in conjunction with the AD7466/AD7467CB evaluation
board and other Analog Devices evaluation boards ending in
the CB designator.
The software allows the user to perform ac tests (fast Fourier
transform) and dc tests (histogram of codes) on the AD7466
and AD7467. See the data sheet in the evaluation board package
for more information.
