DAC8222 Datasheet, PDF (12/15 Pages) Analog Devices – Dual 12-Bit Double-Buffered Multiplying CMOS D/A Converter

DAC8222
Figure 26. Single Supply Operation (Current Switching Mode)
SINGLE SUPPLY OPERATION
CURRENT STEERING MODE
Because the DAC8222’s R-2R resistor ladder terminating resis-
tor is internally connected to AGND, it lends itself well to single
supply operation in the current steering mode. This means that
AGND can be raised above system ground as shown in Figure 26.
The output voltage range will be from +5 V to +10 V depending
on the digital input code and is given by:
V_OUT = V_OS + (n/4096) (V_OS)
where V_OS = Offset Reference Voltage (+5 V in Figure 26)
where n = Decimal Equivalent of the Digital Input Word
VOLTAGE SWITCHING MODE
Figure 27 shows the DAC8222 in a single supply voltage
switching mode of operation. In this configuration, the DAC’s
R-2R ladder acts 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. R_FB pins are not used in this
circuit configuration. The reference input voltage must be main-
tained within +1.25 V of AGND and V_DD from +12 V to +15 V
to preserve device accuracy.
The output voltage expression is given by:
V_OUT = V_REF (n/4096)
where n = 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 DAC8222’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 should
then be 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 device and at the digital and analog power supplies.
A 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 is practical or
allowed, the device should be placed as close as possible to the
system’s single point ground connection. Back-to-back Schottky
diodes should then be connected between AGND and DGND.
POWER SUPPLY DECOUPLING
Power supplies used with the DAC8222 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.
–12–
REV. C