DAC7541AJP-BI BURR-BROWN [Burr-Brown Corporation], DAC7541AJP-BI Datasheet - Page 6

• Manufacturer Part Number: DAC7541AJP-BI
• Description: Low Cost 12-Bit CMOS Four-Quadrant Multiplying DIGITAL-TO-ANALOG CONVERTER
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

FIGURE 2. DAC7541A Equivalent Circuit (All inputs
amplifier, board layout, and power supply decoupling will
all affect the dynamic performance of the DAC7541A. The
use of a compensation capacitor may be required when high-
speed operational amplifiers are used. It may be connected
across the amplifier’s feedback resistor to provide the nec-
essary phase compensation to critically dampen the output.
See Figures 4 and 6.
APPLICATIONS
OP AMP CONSIDERATIONS
The input bias current of the op amp flows through the
feedback resistor, creating an error voltage at the output of
the op amp. This will show up as an offset through all codes
of the transfer characteristics. A low bias current op amp
such as the OPA606 is recommended.
Low offset voltage and V
output impedance of the DAC is modulated with the digital
code. This impedance change (approximately 10k to 30k )
is a change in closed-loop gain to the op amp. The result is
that V
depending on the code. This shows up as a linearity error.
Offset can be adjusted out using Figure 4. Gain may be
adjusted using Figure 5.
UNIPOLAR BINARY OPERATION
(Two-Quadrant Multiplication)
Figure 4 shows the analog circuit connections required for
unipolar binary (two-quadrant multiplication) operation. With
a DC reference voltage or current (positive or negative
polarity) applied at pin 17, the circuit is a unipolar D/A
converter. With an AC reference voltage or current, the
circuit provides two-quadrant multiplication (digitally con-
trolled attenuation). The input/output relationship is shown
in Table I.
V
I
REF
REF
OS
R
10k
will be multiplied by a factor of one to two
LOW).
®
DAC7541A
1/4096
OS
drift are also important. The
I
I
L
L
60pF
90pF
R = 10k
R
I
I
OUT 1
OUT 2
FB
6
FIGURE 3. DAC7541A Equivalent Circuit (All inputs
C
required for stability when using high speed amplifiers. C
is used to cancel the pole formed by the DAC internal
feedback resistance and output capacitance at Out
R
DAC register to 1111 1111 1111, adjust R
V
by omitting R
magnitude.
BIPOLAR FOUR-QUADRANT OPERATION
Figure 6 shows the connections for bipolar four-quadrant
operation. Offset can be adjusted with the A
resistor, with the input code set to 1000 0000 0000. Gain
may be adjusted by varying the feedback resistor of A
input/output relationship is shown in Table II.
TABLE II. Bipolar Codes.
TABLE I. Unipolar Codes.
V
1
1
REF
I
REF
REF
BINARY INPUT
MSB
BINARY INPUT
MSB
in Figure 5 provides full scale trim capability—load the
phase compensation (10 to 25pF) in Figure 4 may be
(4095/4096). Alternatively, full scale can be adjusted
1111 1111 1111
1000 0000 0000
0111 1111 1111
0000 0000 0000
1111 1111 1111
1000 0000 0000
0000 0000 0001
0000 0000 0000
R
10k
HIGH).
1
and R
LSB
LSB
1/4096
2
and trimming the reference voltage
I
I
L
L
ANALOG OUTPUT
+V
0V
–V
–V
ANALOG OUTPUT
–V
–V
–V
0V
REF
REF
REF
REF
REF
REF
(1/2048)
(2048/2048)
(4095/4096)
(2048/4096)
(1/4096)
(2047/2048)
90pF
55pF
1
1
to A
for V
R = 10k
2
summing
1
.
OUT
R
2
I
I
OUT 1
OUT 2
. The
FB
= –
1