
Gain Adjustment
INSTALLATION
GENERAL CONSIDERATIONS
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+
0.01 Fm
DCOM
ACOM
VOUT
VREFOUT
+VCC
-VCC
0.01 Fm+
+12Vto+15V
-12Vto -15V
POWER-SUPPLY AND REFERENCE
DAC712
SBAS023A – SEPTEMBER 2000 – REVISED JULY 2009 .................................................................................................................................................
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Apply the digital input that gives the maximumpositive voltage output. Adjust the gain potentiometeror the gain adjust D/A converter for this positivefull-scale voltage.
Because of the high accuracy of these D/Aconverters, system design problems such asgrounding and contact resistance become veryimportant. A 16-bit converter with a 20V full-scalerange has a 1LSB value of 305mV. With a loadcurrent of 5 µA, series wiring and connectorresistance of only 60m Ωcauses a voltage drop of300 µV. To understand what this means in terms of asystem layout, the resistivity of a typical 1-ouncecopper-clad printed circuit board (PCB) is 1/2m Ωpersquare. For a 5mA load, a 10 mil (0.010 inch) wideprinted circuit conductor 60 milli-inches long results ina voltage drop of 150 µV.
Figure 11. Power-Supply ConnectionsThe analog output of the DAC712 has an LSB size of305 µV ( – 96dB). The noise floor of the D/A converter
The DAC712 has separate ANALOG COMMON andmust remain below this level in the frequency range
DIGITAL COMMON pins. The current through DCOMof interest. The DAC712 noise spectral density (which
is mostly switching transients and are up to 1mAincludes the noise contributed by the internal
peak in amplitude. The current through ACOM isreference) is shown in the Typical Characteristics
typically 5 µA for all codes.section.
Use separate analog and digital ground planes with aWiring 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 toradio frequency interference (RFI) and
help isolate analog from digital signals. Analogelectromagnetic interference (EMI). The key to
signals should be routed as far as possible fromelimination 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/Abe kept close together such that they present a small
converter package, as well as under it in the vicinitycapture cross-section for any external field.
of the analog and power-supply pins, isolates the D/AWire-wrap construction is not recommended.
converter from switching currents. It is recommendedthat DCOM and ACOM be connected directly to theground planes under the package.CONNECTIONS
If several DAC712s are used, or if the DAC712Power-supply decoupling capacitors should be added
shares supplies with other components, connectingas shown in Figure 11 . Best performance occurs
the ACOM and DCOM lines together once at theusing a 1 µF to 10 µF tantalum capacitor at – V
CC
.
power supplies rather than at each chip may giveApplications with less critical settling time may be
better results.able to use 0.01 µF at – V
CC
as well as at +V
CC
. Thecapacitors should be located close to the package.
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