AD5405 datasheet(18/24 Pages) AD

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AD5405

Rev. 0 | Page 18 of 24

These DACs 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 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 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 soldered 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 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

VSS are used to power the output amplifier, while 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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