DAC7802K Burr-Brown Corporation, DAC7802K Datasheet - Page 10

• Manufacturer Part Number: DAC7802K
• Description: Dual Monolithic CMOS 12-Bit Multiplying DIGITAL-TO-ANALOG CONVERTERS
• Manufacturer: Burr-Brown Corporation

If an application requires the D/A to have zero gain error, the
circuit shown in Figure 6 may be used. Resistors R2 and R4
induce a positive gain error greater than worst-case initial
negative gain error. Trim resistors R1 and R3 provide a
variable negative gain error and have sufficient trim range to
correct for the worst-case initial positive gain error plus the
error produced by R2 and R4.
FIGURE 5. Bipolar Configuration.
APPLICATIONS
12-BIT PLUS SIGN DACS
For a bipolar DAC with 13 bits of resolution, two solutions
are possible. As shown in Figure 7, the addition of a precision
difference amplifier and a high speed JFET switch provides
a 12-bit plus sign voltage-output DAC. When the switch
selects the op amp output, the difference amplifier serves as
a non-inverting output buffer. If the analog ground side of the
switch is selected, the output of the difference amplifier is
inverted.
Another option, shown in Figure 8, also produces a 12-bit
plus sign output without the additional switch and digital
control line.
DIGITALLY PROGRAMMABLE ACTIVE FILTER
DAC780X are shown in Figure 9 in a digitally programmable
active filter application. The design is based on the state-
variable filter, Burr-Brown UAF42, an active filter topology
that offers stable and repeatable filter characteristics.
®
1µF
C
DAC7800, 01, 02
D
+
DGND
+5V
V
DD
V
DAC780X
V
DAC A
DAC B
REF B
REF A
R
I
R
I
AGND B
AGND A
OUT A
OUT B
FB A
FB B
20k
20k
R
R
2
6
C
10pF
C
10pF
1
2
10
TABLE III. Bipolar Output Code.
DAC1 and DAC2 can be updated in parallel with a single word
to set the center frequency of the filter. DAC 4, which makes
use of the uncommitted op amp in UAF42, sets the Q of the
filter. DAC3 sets the gain of the filter transfer function without
changing the Q of the filter. The reverse is also true.
The center frequency is determined by f
is the ladder resistance of the D/A (typical value, 10k ) and
C the internal capacitor value (1000pF) of the UAF42. Exter-
nal capacitors can be added to lower the center frequency of
the filter. But the highest center frequency for this circuit will
be about 16kHz because the effective series resistance of the
D/A cannot be less than 10k .
Note that the ladder resistance of the D/A may vary from
device to device. Thus, for best tracking, DAC2 and DAC3
should be in the same package. Some calibration may be
necessary from one filter to another.
–
+
–
+
A3
A1
MSB
10k
R
3
1111 1111 1111
1000 0000 0001
1000 0000 0000
0111 1111 1111
0000 0000 0000
DATA INPUT
R
R
10k
10k
DAC7802 has a single analog common, AGND.
A1–A4, OPA602 or 1/2 OPA2107.
5
5
LSB
–
+
–
+
20k
20k
A4
A2
R
R
4
1
+V
+V
0 Volts
–V
–V
REF
REF
REF
REF
ANALOG OUTPUT
V
V
OUT A
OUT B
C
(2047/2048)
(1/2048)
(1/2048)
(2048/2048)
= 1/2 RC where R