AD5545 datasheet(20/25 Pages) AD

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AD5405

Rev. B | Page 19 of 24

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 AD5405 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 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, 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 DACS

The evaluation board consists of a 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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