Datasheet

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LAYOUT

DAC8544

SLAS420A – MAY 2004 – REVISED JUNE 2005

A precision analog component requires careful layout, adequate bypassing, and clean, well-regulated power

supplies. The following measures should be taken to assure optimum performance of the DAC8544. The

DAC8544 offers dual-supply operation, as it can often be used in close proximity with digital logic,

microcontrollers, microprocessors, and digital signal processors. The more digital logic present in the design and

the higher the switching speed, the more important it becomes to separate the analog and digital ground and

supply planes at the DAC.

Because the DAC8544 has both analog and digital ground pins, return currents can be better controlled and

have less effect on the DAC output error. Ideally, GND would be connected directly to an analog ground plane

and GND to the digital ground plane. The analog ground plane would be separate from the ground connection for

the digital components until they were connected at the power entry point of the system. The power applied to

and V

REF+

(this also applies to V

REF–

if not tied to GND) should be well-regulated and low-noise. Switching

power supplies and dc/dc converters often have high-frequency glitches or spikes riding on the output voltage. In

addition, digital components can create similar high-frequency spikes as their internal logic switches states. This

noise can easily couple into the DAC output voltage through various paths between the power connections and

analog output.

As with the GND connection, V

should be connected to a 5-V power supply plane or trace that is separate

from the connection for digital logic until they are connected at the power entry point. In addition, the 1-µF to

10-µF and 0.1-µF bypass capacitors are strongly recommended. In some situations, additional bypassing may be

required, such as a 100-µF electrolytic capacitor or even a Pi filter made up of inductors and capacitors—all

designed to essentially lowpass-filter the V

supply, removing the high-frequency noise.