13

DAC7617

SBAS185

LAYOUT

A precision analog component requires careful layout, ad-

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

As the DAC7617 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 keep digital noise

from appearing at the converter output.

Due to the DAC7617’s single ground pin, all return currents,

including digital and analog return currents, must flow

through the GND pin. Ideally, GND would be connected

directly to an analog ground plane. This plane would be

separate from the ground connection for the digital compo-

nents until they were connected at the power entry point of

the system (see Figure 3).

The power applied to VDD should be well regulated and low

noise. Switching power supplies and DC/DC converters will

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 connec-

tions and analog output.

As with the GND connection, VDD should be connected to

a +3V 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 3 are strongly recommended. In

some situations, additional bypassing may be required, such

as a 100

µF electrolytic capacitor or even a π filter made up

of inductors and capacitors—all designed to essentially low-

pass filter the +3V supply, removing the high-frequency

noise (see Figure 3).

FIGURE 3. Suggested Power and Ground Connections for a DAC7617 Sharing a +3V Supply with a Digital System.

+3V

Power Supply

Optional

Digital Circuits

DAC7617

Other

Analog

Components

+3V

100

µF

1

µF to

10

µF

Ground

+3V

Ground

V

DD

AGND

0.1

µF

++