AD7846
BIPOLAR OPERATION
Figure 24 shows the AD7846 set up for 10 V bipolar operation.
The AD588 provides precision 5 V tracking outputs that are
fed to the VREF+ and VREF− inputs of the AD7846. The code table
for Figure 24 is shown in Table 9.
Full-scale and bipolar zero adjustment are provided by varying
the gain and balance on the AD588. R2 varies the gain on the
AD588 while R3 adjusts the +5 V and −5 V outputs together
with respect to ground.
+15V
+15V
+5V
For bipolar zero adjustment on the AD7846, load the DAC with
100…000 and adjust R3 until VOUT = 0 V. Full scale is adjusted
R1
39kΩ
4
21
4
6
by loading the DAC with all 1s and adjusting R2 until VOUT
=
V
V
CC
DD
+15V
2
3
1
7
9
9.999694 V.
C1
V
V
V
V
5
7
8
OUT
REF+
OUT
1µF
(–10V TO +10V)
When bipolar zero and full-scale adjustment are not needed, R2
and R3 can be omitted, Pin 12 on the AD588 should be connected
to Pin 11, and Pin 5 should be left floating. If a user wants a 5 V
output range, there are two choices. By tying Pin 6 (RIN) of the
AD7846 to VOUT (Pin 5), the output stage gain is reduced to
unity and the output range is 5 V. If only a positive 5 V reference
is available, bipolar 5 V operation is still possible. Tie VREF− to
0 V and connect RIN to VREF+. This also gives a 5 V output
range. However, the linearity, gain, and offset error specifications
are the same as the unipolar 0 V to 5 V range.
AD588
AD7846*
R2
10kΩ
5
R
6
IN
14
15
16
10
11
REF–
20
DGND
–15V
SIGNAL
GROUND
V
SS
12
8
13
9
R3
100kΩ
–15V
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 24. Bipolar 10 V Operation
Table 9. Offset Binary Code Table for Figure 24
Binary Number in DAC ꢀatch
MUꢀTIPꢀYING OPERATION
The AD7846 is a full multiplying DAC. To obtain four-quadrant
multiplication, tie VREF− to 0 V, apply the ac input to VREF+, and
tie RIN to VREF+. Figure 11 shows the large signal frequency
response when the DAC is used in this fashion.
ꢀSB1
Analog Output (VOUT
)
MSB
1111 1111 1111 1111
1000 0000 0000 0001
1000 0000 0000 0000
0111 1111 1111 1111
0000 0000 0000 0000
+10 (32,767/32,76±) V
+10 (1/32,76±) V
0 V
−10 (1/32,76±) V
−10 (32,76±/32,76±) V
1 LSB = 10 V/215 = 10 V/32,76± = 305 μV.
Rev. G | Page 14 of 24
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