AD5433 datasheet(23/32 Pages) AD

23 / 32 page

AD5424/AD5433/AD5445

Rev. B | Page 23 of 32

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 AD5424/AD5433/AD5445 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 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 to the

package as possible and 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 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 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 to

the device as possible.

EVALUATION BOARD FOR THE

AD5424/AD5433/AD5445

The board consists of a 12-bit AD5445 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 allows the user to

simply write a code to the device.

POWER SUPPLIES FOR EVALUATION BOARD

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

and VSS are used to power the output amplifier, while the

+5 V VDD and VSS are 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.

Link1 (LK1) is provided to allow selection between the on-

board reference (ADR01) and an external reference applied

through J2.

AD5433 Datasheet(PDF) 23 Page - Analog Devices

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