AD5428 datasheet(23/32 Pages) AD

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Data Sheet

AD5428/AD5440/AD5447

Rev. D | Page 23 of 32

PCB LAYOUT AND POWER SUPPLY DECOUPLING

In any circuit where accuracy is important, careful

consideration of the power supply and ground return layout

helps to ensure the rated performance. The printed circuit

board on which the AD5428/AD5440/AD5447 is mounted

should be designed so that the analog and digital sections are

separate 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

as possible to the device.

These DACs should have ample supply bypassing of 10 μF in

parallel with 0.1 μF on the supply located as close as possible to

the package, ideally right up against the device. The 0.1 μF

capacitor should have low effective series resistance (ESR) and

low effective series inductance (ESI), like the common ceramic

types of capacitors 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.

Components, such as clocks, that produce fast-switching signals

should be shielded with digital ground to avoid radiating noise

to other parts of the board, and they 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 on the board. A

microstrip technique is by far the best method, but its use is not

always possible with a double-sided board. In this technique,

the component side of the board is dedicated to the ground

plane, and signal traces are placed on the soldered side.

It is good practice to use 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 VREF and RFB should also be

matched to minimize gain error. To maximize high frequency

performance, the I-to-V amplifier should be located as close as

possible to the device.

EVALUATION BOARD FOR THE AD5447

The evaluation board consists of an AD5447 DAC 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.

POWER SUPPLIES FOR THE EVALUATION BOARD

The board requires ±12 V and +5 V supplies. The +12 V VDD

and −12 V VSS are used to power the output amplifier; the +5 V

is used to power the DAC (VDD1) and transceivers (VCC).

Both supplies are decoupled to their respective ground plane

with 10 μF tantalum and 0.1 μF ceramic capacitors.

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