Datasheet

DAC7731
16
SBAS249B
www.ti.com
LAYOUT
A precision analog component requires careful layout, adequate
bypassing, and clean, well-regulated power supplies. The
DAC7731 offers separate digital and analog supplies, as 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 switching speed,
the more important it will become to separate the analog and
digital ground and supply planes at the device.
Since the DAC7731 has both analog and digital ground pins,
return currents can be better controlled and have less effect
on the DAC output error. Ideally, AGND would be connected
directly to an analog ground plane and DGND 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 voltages applied to V
CC
and V
SS
should be well regulated
and low noise. Switching power supplies and DC/DC convert-
ers 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.
In addition, a 1µF to 10µF bypass capacitor in parallel with a
0.1µF bypass capacitor is strongly recommended for each
supply input. In some situations, additional bypassing may be
required, such as a 100µF electrolytic capacitor or even a Pi
filter made up of inductors and capacitors–all designed to
essentially low-pass filter the analog supplies, removing any
high frequency noise components.