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12

DAC7614

LAYOUT

A precision analog component requires careful layout, ad-

equate bypassing, and clean, well-regulated power supplies.

As the DAC7614 offers single-supply operation, it will 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 switch-

ing speed, the more difficult it will be to achieve good

performance from the converter.

Because the DAC7614 has a single ground pin, all return

currents, including digital and analog return currents, must

flow through the GND pin. Ideally, GND would be con-

nected directly to an analog ground plane. This plane would

be separate from the ground connection for the digital

components until they were connected at the power entry

point of the system (see Figure 4).

The power applied to VDD (as well as VSS, if not grounded)

should be well regulated and low noise. Switching power

supplies and DC/DC converters will often have high-fre-

quency glitches or spikes riding on the output voltage. In

addition, digital components can create similar high-fre-

quency 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, VDD should be connected to

a +5V 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 10µF and 0.1µF

capacitors shown in Figure 4 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 +5V supply, removing the high frequency

noise (see Figure 4).

FIGURE 4. Suggested Power and Ground Connections for a DAC7614 Sharing a +5V Supply with a Digital System.

+5V

Power Supply

Optional

Digital Circuits

DAC7614

Other

Analog

Components

+5V

100µF

1µF to

10µF

Ground

+5V

Ground

V

DD

GND

0.1µF

++