DAC8248_15 Datasheet, PDF (14/16 Pages) Analog Devices – Dual 12-Bit (8-Bit Byte) Double-Buffered CMOS D/A Converter

DAC8248
ground as shown in Figure 9. The output voltage will be be-
tween +5 V and +10 V depending on the digital input code.
The output expression is given by:
V_OUT = V_OS × (D/4096)(V_OS)
where V_OS = Offset Reference Voltage (+5 V in Figure 9)
D = Decimal Equivalent of the Digital Input Word
VOLTAGE SWITCHING MODE
Figure 10 shows the DAC8248 in another single supply configu-
ration. The R-2R ladder is used in the voltage switching mode
and functions as a voltage divider. The output voltage (at the
V_REF pin) exhibits a constant impedance R (typically 11 kΩ) and
must be buffered by an op amp. The R_FB pins are not used and
are left open. The reference input voltage must be maintained
within +1.25 V of AGND, and V_DD between +12 V and +15 V;
this ensures that device accuracy is preserved.
The output voltage expression is given by:
V_OUT = V_REF (D/4096)
where D = Decimal Equivalent of the Digital Input Word
APPLICATIONS TIPS
GENERAL GROUND MANAGEMENT
Grounding techniques should be tailored to each individual sys-
tem. Ground loops should be avoided, and ground current paths
should be as short as possible and have a low impedance.
The DAC8248’s AGND and DGND pins should be tied to-
gether at the device socket to prevent digital transients from ap-
pearing at the analog output. This common point then becomes
the single ground point connection. AGND and DGND is then
brought out separately and tied to their respective power supply
grounds. Ground loops can be created if both grounds are tied
together at more than one location, i.e., tied together at the de-
vice and at the digital and analog power supplies.
PC board ground plane can be used for the single point ground
connection should the connections not be practical at the device
socket. If neither of these connections are practical or allowed,
then the device should be placed as close as possible to the sys-
tems single point ground connection. Back-to-back Schottky di-
odes should then be connected between AGND and DGND.
POWER SUPPLY DECOUPLING
Power supplies used with the DAC8248 should be well filtered
and regulated. Local supply decoupling consisting of a 1 µF to
10 µF tantalum capacitor in parallel with a 0.1 µF ceramic is
highly recommended. The capacitors should be connected be-
tween the V_DD and DGND pins and at the device socket.
Figure 9. Single Supply Operation (Current Switching Mode)
–14–
REV. B