Datasheet

DAC8043
Rev. E | Page 13 of 16
Bipolar Operation (4-Quadrant)
Figure 19 details a suggested circuit for bipolar, or offset binary,
operation. Table 7 shows the digital input to analog output
relationship. The circuit uses offset binary coding. Twos comple-
ment code can be converted to offset binary by software
inversion of the MSB or by the addition of an external inverter
to the MSB input.
Table 7. Bipolar (Offset Binary) Code Table
1, 2
Digital Input Nominal Analog Output
MSB LSB (V
OUT
as Shown in Figure 19)
1111 1111 1111







2048
2047
REF
V
1000 0000 0001







2048
1
REF
V
1000 0000 0000 0
0111 1111 1111







2048
1
REF
V
0000 0000 0001







2048
2047
REF
V
0000 0000 0000







2048
2048
REF
V
1
Nominal full scale for Figure 19 circuits is given by







2048
2047
REF
VFS
2
Nominal LSB magnitude for Figure 19 circuits is given by







2048
1
REF
VLSB
Resistors R
3
, R
4
, and R
5
must be selected to match within 0.01%,
and they all must be of the same (preferably metal foil) type to
ensure temperature coefficient matching. Mismatching between
R
3
and R
4
causes offset and full-scale errors, while an R
5
to R
4
and R
3
mismatch results in full-scale error.
Calibration is performed by loading the DAC register with 1000
0000 0000 and adjusting R
1
until V
OUT
= 0 V. R
1
and R
2
may be
omitted, adjusting the ratio of R
3
to R
4
to yield V
OUT
= 0 V. Full
scale can be adjusted by loading the DAC register with 1111
1111 1111 and either adjusting the amplitude of V
REF
or the
value of R
5
until the desired V
OUT
is achieved.
Analog/Digital Division
The transfer function for the DAC8043 connected in the
multiplying mode, as shown in Figure 16, Figure 17, and
Figure 19, is







12321
2
...
222
12321
IN
O
AAAA
VV
where
A
X
assumes a value of 1 for an on bit and 0 for an off bit.
The transfer function is modified when the DAC is connected
in the feedback of an operational amplifier, as shown in Figure 18
and becomes















4321
2
...
222
12321
IN
O
AAAA
V
V
The previous transfer function is the division of an analog
voltage (V
REF
) by a digital word. The amplifier goes to the rails
with all bits off because division by zero is infinity. With all bits
on the gain is 1 (±1 LSB). The gain becomes 4096 with the LSB,
Bit 12, on.
DAC8043
R
FB
V
DD
5V
LD SRI CLK
V
REF
I
OUT
GND
DIGITAL
INPUT
V
IN
00271-019
OP42
2
3
6
V
OUT
Figure 18. Analog/Digital Divider
00271-018
V
OUT
CONTROL
INPUTS
SERIAL
DATA
INPUT
ANALOG
COMMON
V
IN
R
2
50Ω
R
3
10kΩ
5V
R
4
20kΩ
R
5
20kΩ
R
1
100Ω
C
1
10.33pF
1/2
OP200
A
2
DAC8043
R
FB
V
DD
V
REF
I
OUT
GND
CONTROL
BITS
SRI
1/2
OP200
A
1
Figure 19. Bipolar Operation (4-Quadrant, Offset Binary)