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AD7839
–8–
REV. 0
Unipolar Configuration
Figure 11 shows the AD7839 in the unipolar binary circuit
configuration. The VREF(+) input of the DAC is driven by the
AD586, a +5 V reference. VREF(–) is tied to ground. Table II
gives the code table for unipolar operation of the AD7839.
Other suitable references include the REF02, a precision +5 V
reference, and the REF195, a low dropout, micropower preci-
sion +5 V reference.
AD7839*
VDD
VCC
VREF(+)
VOUT
DUTGND
GND
VSS
VREF(–)
SIGNAL
GND
–15V
VOUT
(0 TO +10V)
+5V
+15V
AD586
R1
10k
2
6
5
4
8
C1
1 F
SIGNAL
GND
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 11. Unipolar +10 V Operation
Offset and gain may be adjusted in Figure 11 as follows: To
adjust offset, disconnect the VREF(–) input from 0 V, load the
DAC with all 0s and adjust the VREF(–) voltage until VOUT = 0 V.
For gain adjustment, the AD7839 should be loaded with all 1s
and R1 adjusted until VOUT = 2 VREF(+) – 1 LSB = 10 V(8191/
8192) = 9.99878 V.
Many circuits will not require these offset and gain adjustments.
In these circuits R1 can be omitted. Pin 5 of the AD586 may be
left open circuit and Pin 2 (VREF(–)) of the AD7839 tied to 0 V.
Table II. Code Table for Unipolar Operation
Binary Number in DAC Register
Analog Output
MSB
LSB
(VOUT)
1
1111
2 VREF (8191/8192) V
1
0000
2 VREF (4096/8192) V
0
1111
2 VREF (4095/8192) V
0
0000
0001
2 VREF (1/8192) V
0
0000
0 V
NOTES
VREF = VREF(+); VREF(–) = 0 V for unipolar operation.
For VREF(+) = +5 V, 1 LSB = +10 V/2
13 = +10 V/8192 = 1.22 mV.
Bipolar Configuration
Figure 12 shows the AD7839 set up for
±10 V operation. The
AD588 provides precision
±5 V tracking outputs that are fed to
the VREF(+) and VREF(–) inputs of the AD7839. The code table
for bipolar operation of the AD7839 is shown in Table III.
In Figure 12, full-scale and bipolar zero adjustments are pro-
vided by varying the gain and balance on the AD588. R2 varies
the gain on the AD588 while R3 adjusts the offset of both the
+5 V and –5 V outputs together with respect to ground.
For bipolar-zero adjustment, the DAC is loaded with
1000 . . . 0000 and R3 is adjusted until VOUT = 0 V. Full
scale is adjusted by loading the DAC with all 1s and adjusting
R2 until VOUT = 10(4095/4096) V = 9.997559 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.
AD7839*
VDD
VCC
VREF(+)
VOUT
DUTGND
GND
VSS
VREF(–)
SIGNAL
GND
–15V
VOUT
(–10V TO +10V)
+5V
+15V
*ADDITIONAL PINS OMITTED FOR CLARITY
R1
39k
C1
1 F
R2
100k
R3
100k
AD588
46
2
3
1
14
15
16
7
9
5
10
11
12
8 13
Figure 12. Bipolar
±10 V Operation
Table III. Code Table for Bipolar Operation
Binary Number in DAC
Register
Analog Output
MSB
LSB
(VOUT)
1
1111
2[VREF(–) + VREF (8191/8192)] V
1
0000
0001
2[VREF(–) + VREF (4097/8192)] V
1
0000
2[VREF(–) + VREF (4096/8192)] V
0
1111
2[VREF(–) + VREF (4095/8192)] V
0
0000
0001
2[VREF(–) + VREF (1/8192)] V
0
0000
2[VREF(–)] V
NOTES
VREF = (VREF(+) – VREF(–)).
For VREF(+) = +5 V, and VREF(–) = –5 V, VREF = 10 V, 1 LSB = 2 VREF V/2
13 =
20 V/8192 = 2.44 mV.
CONTROLLED POWER-ON OF THE OUTPUT STAGE
A block diagram of the output stage of the AD7839 is shown in
Figure 13. It is capable of driving a load of 5 k
in parallel with
50 pF. G1 to G6 are transmission gates used to control the
power on voltage present at VOUT. On power up G1 and G2 are
also used in conjunction with the
CLR input to set V
OUT to the
user defined voltage present at the DUTGND pin. When
CLR
is taken back high, the DAC outputs reflect the data in the DAC
registers.
G1
G2
G4
G3
G6
G5
DUTGND
VOUT
R
R = 60k
14k
DAC
Figure 13. Block Diagram of AD7839 Output Stage