AD7225
Rev. C | Page 14 of 24
BIPOLAR OUTPUT OPERATION
Each of the DACs of the AD7225 can be individually confi-
gured to provide bipolar output operation. This is possible
using one external amplifier and two resistors per channel.
Figure 17 shows a circuit used to implement offset binary
coding (bipolar operation) with DAC A (DAC Channel A)
of the AD7225. In this case,
(
)
(
)
REF
A
OUT
V
R
R2
V
D
R1
R2
V
×
×
+
=
1
With R1 = R2
(
) ( )
REF
A
OUT
V
D
V
×
=
1
2
where DA is a fractional representation of the digital word in
Latch A (0 ≤ DA ≤ 255/256).
Mismatch between R1 and R2 causes gain and offset errors and,
therefore, these resistors must match and track over tempera-
ture. The AD7225 can be operated in single supply or from
positive/negative supplies
. Table 8 shows the digital code vs.
R1 = R2.
+15V
–15V
VDD
VSS
AGND
DGND
VOUTA
DAC A
AD7225*
VREFA
R2
VOUT
R1
VREF
R1, R2 = 10k
± 0.1%.
*DIGITAL INPUTS OMITTED
FOR CLARITY.
00986-
017
Figure 17. Bipolar Output Circuit
Table 8. Bipolar (Offset Binary) Code Table
DAC Latch Contents
Analog Output
MSB
LSB
1111
( )
128
127
REF
V
+
1000
0001
( )
128
1
REF
V
+
1000
0000
0 V
0111
1111
( )
128
1
REF
V
0000
0001
( )
128
127
REF
V
0000
( )
REF
V
=
1
128