AD7846
UNIPOLAR BINARY OPERATION
Figure 23 shows the AD7846 in the unipolar binary circuit
configuration. The DAC is driven by the AD586 +5 V reference.
Because RIN is tied to 0 V, the output amplifier has a gain of 2
and the output range is 0 V to +10 V. If a 0 V to +5 V range is
required, RIN should be tied to VOUT, configuring the output
stage for a gain of 1. Table 8 gives the code table for the circuit
of Figure 23.
Table 8. Code Table for Figure 23
Binary Number in DAC ꢀatch
MSB
ꢀSB1
Analog Output (VOUT
)
1111 1111 1111 1111
1000 0000 0000 0000
0000 0000 0000 0001
0000 0000 0000 0000
+10 (65,535/65,536) V
+10 (32,76±/65,536) V
+10 (1/65,536) V
0 V
+15V
+5V
1 LSB = 10 V/216 = 10 V/65,536 = 152 ꢀV.
4
21
Offset and gain can be adjusted in Figure 23 as follows:
2
V
V
DD
CC
•
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 AD7846 should be loaded with all
1s and R1 adjusted until VOUT = 10 (65,535)/(65,536) =
9.999847 V. If a simple resistor divider is used to vary the
V
OUT
(0V TO +10V)
5
V
6
5
7
8
V
OUT
REF+
AD586
8
R1
10kΩ
AD7846*
C1
R
6
IN
1µF
4
•
V
REF–
20
DGND
V
SS
SIGNAL
GROUND
VREF− voltage, it is important that the temperature
coefficients of these resistors match that of the DAC input
resistance (−300 ppm/°C). Otherwise, extra offset errors are
introduced over temperature. Many circuits do not require
these offset and gain adjustments. In these circuits, R1 can
be omitted. Pin 5 of the AD586 can be left open circuit and
Pin 8 (VREF−) of the AD7846 tied to 0 V.
*ADDITIONAL PINS
OMITTED FOR CLARITY
–15V
Figure 23. Unipolar Binary Operation
Rev. G | Page 13 of 24
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