Datasheet

AD7846
Rev. G | Page 13 of 24
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 R
IN
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, R
IN
should be tied to V
OUT
, configuring the output
stage for a gain of 1. Tabl e 8 gives the code table for the circuit
of Figure 23.
R
IN
V
OUT
DGND
+15
V
+5
V
V
CC
V
DD
V
REF+
V
REF–
R1
10kΩ
C1
1µF
SIGNAL
GROUND
–15V
*ADDITIONAL PINS
OMITTED FOR CLARITY
AD7846*
AD586
V
OUT
(0V TO +10V)
V
SS
2
5
4
67
21
5
20
6
4
8
8
08490-023
Figure 23. Unipolar Binary Operation
Table 8. Code Table for Figure 23
Binary Number in DAC Latch
MSB LSB
1
Analog Output (V
OUT
)
1111 1111 1111 1111 +10 (65,535/65,536) V
1000 0000 0000 0000 +10 (32,768/65,536) V
0000 0000 0000 0001 +10 (1/65,536) V
0000 0000 0000 0000 0 V
1
LSB = 10 V/2
16
= 10 V/65,536 = 152 µV.
Offset and gain can be adjusted in Figure 23 as follows:
• To adjust offset, disconnect the V
REF−
input from 0 V, load
the DAC with all 0s, and adjust the V
REF−
voltage until V
OUT
= 0 V.
• For gain adjustment, the AD7846 should be loaded with all
1s and R1 adjusted until V
OUT
= 10 (65,535)/(65,536) =
9.999847 V. If a simple resistor divider is used to vary the
V
REF−
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 (V
REF−
) of the AD7846 tied to 0 V.