Datasheet

Gain Adjustment
INSTALLATION
GENERAL CONSIDERATIONS
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+
0.01 Fm
DCOM
ACOM
V
OUT
V
REFOUT
+V
CC
-V
CC
0.01 Fm
+
+12Vto+15V
-12Vto -15V
POWER-SUPPLY AND REFERENCE
DAC712
SBAS023A – SEPTEMBER 2000 – REVISED JULY 2009 ................................................................................................................................................. www.ti.com
Apply the digital input that gives the maximum
positive voltage output. Adjust the gain potentiometer
or the gain adjust D/A converter for this positive
full-scale voltage.
Because of the high accuracy of these D/A
converters, system design problems such as
grounding and contact resistance become very
important. A 16-bit converter with a 20V full-scale
range has a 1LSB value of 305mV. With a load
current of 5 µ A, series wiring and connector
resistance of only 60m Ω causes a voltage drop of
300 µ V. To understand what this means in terms of a
system layout, the resistivity of a typical 1-ounce
copper-clad printed circuit board (PCB) is 1/2m Ω per
square. For a 5mA load, a 10 mil (0.010 inch) wide
printed circuit conductor 60 milli-inches long results in
a voltage drop of 150 µ V.
Figure 11. Power-Supply Connections
The analog output of the DAC712 has an LSB size of
305 µ V ( – 96dB). The noise floor of the D/A converter
The DAC712 has separate ANALOG COMMON and
must remain below this level in the frequency range
DIGITAL COMMON pins. The current through DCOM
of interest. The DAC712 noise spectral density (which
is mostly switching transients and are up to 1mA
includes the noise contributed by the internal
peak in amplitude. The current through ACOM is
reference) is shown in the Typical Characteristics
typically 5 µ A for all codes.
section.
Use separate analog and digital ground planes with a
Wiring to high-resolution D/A converters should be
single interconnection point to minimize ground loops.
routed to provide optimum isolation from sources of
The analog pins are located adjacent to each other to
radio frequency interference (RFI) and
help isolate analog from digital signals. Analog
electromagnetic interference (EMI). The key to
signals should be routed as far as possible from
elimination of RF radiation or pickup is a small loop
digital signals and should cross them at right angles.
area. Signal leads and the return conductors should
A solid analog ground plane around the D/A
be kept close together such that they present a small
converter package, as well as under it in the vicinity
capture cross-section for any external field.
of the analog and power-supply pins, isolates the D/A
Wire-wrap construction is not recommended.
converter from switching currents. It is recommended
that DCOM and ACOM be connected directly to the
ground planes under the package.
CONNECTIONS
If several DAC712s are used, or if the DAC712
Power-supply decoupling capacitors should be added
shares supplies with other components, connecting
as shown in Figure 11 . Best performance occurs
the ACOM and DCOM lines together once at the
using a 1 µ F to 10 µ F tantalum capacitor at – V
CC
.
power supplies rather than at each chip may give
Applications with less critical settling time may be
better results.
able to use 0.01 µ F at – V
CC
as well as at +V
CC
. The
capacitors should be located close to the package.
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