AD7846
BIPOLAR OPERATION
Other Output Voltage Ranges
Figure 19 shows the AD7846 set up for 10 V bipolar opera-
tion. The AD588 provides precision 5 V tracking outputs
which are fed to the VREF+ and VREF– inputs of the AD7846.
The code table for Figure 19 is shown in Table IV.
In some cases, users may require output voltage ranges other
than those already mentioned. One example is systems which
need the output voltage to be a whole number of millivolts (i.e.,
1 mV, 2 mV, etc.). If the AD689 (8.192 V reference) is used
with the AD7846 as in Figure 20, then the LSB size is 125 µV.
This makes it possible to program whole millivolt values at the
Output. Table V shows the code table for Figure 20.
+15V
R1
+15V
+5V
39k⍀
4
+15V
+5V
V
V
DD
CC
+15V
V
C1
1F
OUT
V
V
OUT
REF+
(–10V TO +10V)
V
V
DD
CC
V
AD588
OUT
(0V TO 8.192V)
V
AD7846*
R2
10k⍀
OUT
V
REF+
R
IN
AD689
AD7846*
R
IN
V
REF–
DGND
SIGNAL
GROUND
–15V
V
V
DGND
REF–
SS
V
SS
SIGNAL GROUND
R3
100k⍀
*ADDITIONAL PINS
OMITTED FOR CLARITY
*ADDITIONAL PINS
OMITTED FOR CLARITY
–15V
–15V
Figure 19. Bipolar 10 V Operation
Table IV. Offset Binary Code Table for Figure 19
Figure 20. Unipolar Output with AD689
Table V. Code Table for Figure 20
Binary Number
in DAC Latch
Analog Output
(VOUT
Binary Number
in DAC Latch
Analog Output
(VOUT
)
)
MSB
LSB
MSB
LSB
1111 1111 1111 1111
1000 0000 0000 0001
1000 0000 0000 0000
0111 1111 1111 1111
0000 0000 0000 0000
+10 (32767/32768) V
+10 (1/32768) V
0 V
–10 (1/32768) V
–10 (32768/32768) V
1111 1111 1111 1111
1000 0000 0000 0000
0000 0000 0000 1000
0000 0000 0000 0100
0000 0000 0000 0010
0000 0000 0000 0001
8.192 V (65535/65536) = 8.1919 V
8.192 V (32768/65536) = 4.096 V
8.192 V (8/65536) = 0.001 V
8.192 V (4/65536) = 0.0005 V
8.192 V (2/65536) = 0.00025 V
8.192 V (1/65536) = 0.000125 V
NOTE
1 LSB = 10 V/215 = 10 V/32768 = 305 µV.
NOTE
1 LSB = 8.192 V/2l6 = 125 µV.
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.
Multiplying Operation
The AD7846 is a full multiplying DAC. To get four-quadrant
multiplication, tie VREF– to 0 V, apply the ac input to VREF+ and
tie RIN to VREF+. Figure 6 shows the Large Signal Frequency
Response when the DAC is used in this fashion.
For bipolar zero adjustment on the AD7846, load the DAC with
100 . . . 000 and adjust R3 until VOUT = 0 V. Full scale is ad-
justed by loading the DAC with all 1s and adjusting R2 until
VOUT = 9.999694 V.
When bipolar zero and full scale adjustment are not needed, R2
and R3 can be omitted, Pin 12 on the AD588 should be con-
nected 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 pos-
sible. Tie VREF– to 0 V and connect RIN to VREF+. This will also
give a 5 V output range. However, the linearity, gain, and
offset error specifications will be the same as the unipolar 0 V to
+5 V range.
REV. E
–9–
ADI [ ADI ]
