AD5444 Analog Devices, AD5444 Datasheet - Page 23

• Manufacturer Part Number: AD5444
• Description: 12-Bit High Bandwidth Multiplying DAC with Serial Interface
• Manufacturer: Analog Devices

Specifications of AD5444

• Resolution (bits): 12bit
• Dac Update Rate: 2.7MSPS
• Dac Settling Time: 40ns
• 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 considera-
tion of the power supply and ground return layout helps to
ensure the rated performance. The printed circuit boards on
which the AD5444/AD5446 are mounted should be designed
so the analog and digital sections are separated and confined to
certain areas of the board. If the DACs are in systems in which
multiple devices require a AGND-to-DGND connection, the
connection should be made at one point only. The star ground
point should be established as close as possible to the devices.
The DAC should have ample supply bypassing of 10 μF in
parallel with 0.1 μF on the supply located as close to the pack-
age 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 oppo-
site sides of the board should run at right angles to each other.
This reduces the effects of feedthrough throughout the board.
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A microstrip technique, by far the best, is not always possible
with a double-sided board. In this technique, the component
side of the board is dedicated to the ground plane, while signal
traces are placed on the solder side.
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 high frequency
performance, the I-to-V amplifier should be located as close
to the device as possible.
EVALUATION BOARD FOR THE DAC
The evaluation board consists of an AD5444 or AD5446 DAC
and a current-to-voltage amplifier, AD8065. Included on the
evaluation board is a 10 V reference, ADR01. An external
reference can also be applied via an SMB input.
The evaluation kit consists of a CD with self-installing PC
software to control the DAC. The software allows the user
to write a code to the device.
POWER SUPPLIES FOR THE EVALUATION BOARD
The board requires ±12 V and +5 V supplies. The ±12 V V
and V
supply 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.
SS
are used to power the output amplifier, while the +5 V
REF
and R
DD1
AD5444/AD5446
) and transceivers (V
FB
should also be
DD
CC
).