UG-745
EVAL-AD7625FMCZ/EVAL-AD7626FMCZ User Guide
Rev. A | Page 6 of 28
REFERENCE OPTIONS
The
AD7625
/
AD7626
have an internal 4.096 V reference along
with an internal buffer that can be used with an external reference,
or the devices can be used directly with an external 4.096 V
reference. The
EVAL-AD7625FMCZ
/
EVAL-AD7626FMCZ
evaluation boards can be configured to use any of these
references. To use the internal ADC reference, leave LK2 and
LK3 open. To use the
ADR4540
, insert LK3 and leave LK2
open. (The 4.096V output of the
ADR4540
is buffered by an
AD8031
in a unity-gain configuration.)
To use the internal reference buffer on the
AD7625
/
AD7626
REFIN pin, insert LK2 and leave LK3 open. The 1.2 V reference
voltage is applied to REFIN prior to the internal buffer in the
AD7625
/
AD7626
, which creates the required internal 4.096 V
reference. (The 1.2 V output of the
ADR3412
is buffered by an
AD8031
in a unity-gain configuration). The various options for
using this reference are controlled by the EN1 and EN0 pins
(EN bits on software), as described in the
AD7625
/
AD7626
data sheets.
LAYOUT GUIDELINES
When laying out the printed circuit board (PCB) for the
AD7625
/
AD7626
, follow these recommended guidelines to
obtain the maximum performance from the converter.
•
Solder the
AD7625
/
AD7626
(Pin 33) directly to the PCB
and connect the paddle to the ground plane of the board
using multiple vias.
•
Decouple all the power supply pins (VDD1, VDD2, and
VIO) and the REF pin with low ESR and low ESL ceramic
capacitors, typically 10 µF and 100 nF, placed close to the
DUT (U1) and connected using short, wide traces. This
provides low impedance paths and reduces the effect of
glitches on the power supply lines.
•
Use a 50 Ω single-ended trace and a 100 Ω differential trace.
•
Separate analog and digital sections and keep power supply
circuitry away from the
AD7625
/
AD7626
.
•
Avoid running digital lines under the device as well as
crossover of digital and analog signals because these couple
noise into the
AD7625
/
AD7626
.
•
Do not run fast switching signals, such as CNV or clocks,
near analog signal paths.
•
Remove the ground and power plane beneath the input
(including feedback) and output pins of the amplifiers (U6,
U13, and U15), because they create an undesired capacitor.
BASIC HARDWARE SETUP
The
EVAL-AD7625FMCZ
/
EVAL-AD7626FMCZ
evaluation
boards connect to the
EVAL-SDP-CH1Z
SDP board. The SDP
board is the controller board, which is the communication link
between the PC and the main evaluation board.
1.
Figure 1 shows a photograph of the connections made
between the
EVAL-AD7625FMCZ
/
EVAL-AD7626FMCZ
daughter board and the
EVAL-SDP-CH1Z
SDP controller
board.
2.
Install the
AD7625
/
AD7626
evaluation software. Ensure
that the SDP board is disconnected from the USB port of
the PC while installing the software. The PC must be
restarted after the installation.
3.
Before connecting power, connect the 160-pin FMC
connector (J7) on the evaluation board to Connector J4 on
the SDP board. Nylon screws are included in the evaluation
kit and can be used to ensure that the evaluation board and
the SDP board are connected firmly together.
4.
Connect the 12 V power supply adapter included in the kit
to the SDP board.
5.
Connect the SDP board to the PC via the USB cable.
Windows® XP users may need to search for the
EVAL-
SDP-CH1Z
drivers. Choose to automatically search for the
drivers for the SDP board if prompted by the operating
system.
6.
Launch the
AD7625
/
AD7626
evaluation software from the
Analog Devices
subfolder in the
Programs
menu. The full
software installation procedure is described in the Evaluation
Board Software section.
