AD5426 Analog Devices, AD5426 Datasheet - Page 23

• Manufacturer Part Number: AD5426
• Description: High Bandwidth CMOS 8-Bit Serial Interface Multiplying D/A Converter
• Manufacturer: Analog Devices

Specifications of AD5426

• Resolution (bits): 8bit
• Dac Update Rate: 2.47MSPS
• Dac Settling Time: 50ns
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Ser,SPI

PCB LAYOUT AND POWER SUPPLY DECOUPLING
In any circuit where accuracy is important, careful consider-
ation of the power supply and ground return layout helps to
ensure the rated performance. The printed circuit board on
which the AD5426/AD5432/AD5443 is mounted should be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. If the DAC is in a
system where multiple devices require an AGND-to-DGND
connection, the connection should be made at one point only.
The star ground point should be established as close to the
device as possible.
The DAC should have ample supply bypassing of 10 μF in
parallel with 0.1 μF on the supply located as close to the package
as possible, ideally right up against the device. The 0.1 μF
capacitor should have low effective series resistance (ESR) and
effective series inductance (ESI), like the common ceramic
types that provide a low impedance path to ground at high
frequencies to handle transient currents due to internal logic
switching. Low ESR, 1 μF to 10 μF tantalum or electrolytic
capacitors should also be applied at the supplies to minimize
transient disturbance and filter out low frequency ripple.
Fast switching signals such as clocks should be shielded with
digital ground to avoid radiating noise to other parts of the
board and should never be run near the reference inputs.
Avoid crossover of digital and analog signals. Traces on opposite
sides of the board should run at right angles to each other. This
reduces the effects of feedthrough through the board. A micro-
strip technique is by far the best, but not always possible with a
double-sided board. In this technique, the component side of the
board is dedicated to ground plane while signal traces are placed
on the solder side.
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It is good practice to employ compact, minimum lead length
PCB layout design. Leads to the input should be as short as
possible to minimize IR drops and stray inductance.
The PCB metal traces between V
matched to minimize gain error. To maximize on high
frequency performance, the I-to-V amplifier should be
located as close to the device as possible.
EVALUATION BOARD FOR THE
AD5426/AD5432/AD5443 SERIES OF DACS
The evaluation board consists of a 12-bit AD5443 and a
current-to-voltage amplifier, the AD8065. Included on the
evaluation board is a 10 V reference, the ADR01. An external
reference may also be applied via an SMB input.
The evaluation kit consists of a CD-ROM with self-installing
PC software to control the DAC. The software simply allows the
user to write a code to the device.
OPERATING THE EVALUATION BOARD
Power Supplies
The board requires ±12 V and +5 V supplies. The +12 V V
and V
is used to power the DAC (V
Both supplies are decoupled to their respective ground plane
with 10 μF tantalum and 0.1 μF ceramic capacitors. Link1 (LK1)
is provided to allow selection between the on-board reference
(ADR01) or an external reference applied through J2. For the
AD5426/AD5432/AD5443 use Link2 in the SDO position.
SS
are used to power the output amplifier, while the +5 V
AD5426/AD5432/AD5443
DD1
) and transceivers (V
REF
and R
FB
should also be
CC
).
DD