AD7846(RevE) Ver la hoja de datos (PDF) - Analog Devices
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AD7846 Datasheet PDF : 16 Pages
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AD7846
BIPOLAR OPERATION
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.
C1
1F
R2
10k⍀
+15V
R1
39k⍀
+15V
+15V
4
VDD
VREF+
+5V
VCC
VOUT
AD588
AD7846*
RIN
VOUT
(–10V TO +10V)
–15V
VREF– DGND
VSS
SIGNAL
GROUND
R3
100k⍀
*ADDITIONAL PINS
–15V OMITTED FOR CLARITY
Figure 19. Bipolar ±10 V Operation
Table IV. Offset Binary Code Table for Figure 19
Binary Number
in DAC Latch
MSB
LSB
1111 1111 1111 1111
1000 0000 0000 0001
1000 0000 0000 0000
0111 1111 1111 1111
0000 0000 0000 0000
Analog Output
(VOUT)
+10 (32767/32768) V
+10 (1/32768) V
0V
–10 (1/32768) V
–10 (32768/32768) V
NOTE
1 LSB = 10 V/215 = 10 V/32768 = 305 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.
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.
Other Output Voltage Ranges
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
+5V
AD689
VDD
VREF+
VCC
VOUT
AD7846* RIN
VOUT
(0V TO 8.192V)
SIGNAL GROUND
VREF–
VSS
DGND
*ADDITIONAL PINS
OMITTED FOR CLARITY
–15V
Figure 20. Unipolar Output with AD689
Table V. Code Table for Figure 20
Binary Number
in DAC Latch
MSB
LSB
1111 1111 1111 1111
1000 0000 0000 0000
0000 0000 0000 1000
0000 0000 0000 0100
0000 0000 0000 0010
0000 0000 0000 0001
Analog Output
(VOUT)
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 = 8.192 V/2l6 = 125 µV.
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.
REV. E
–9–
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