DAC8222

–12–

REV. C

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:

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

Ω) and

circuit configuration. The reference input voltage must be main-

to preserve device accuracy.

The output voltage expression is given by:

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-