Datasheet

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,
( ) ( )
REFREF
A
OUT
V
R
R2
VD
R1
R2
V ×






−×






+=
1
1
With R1 = R2
( )
( )
REF
A
OUT
VDV
×−=
12
where D
A
is a fractional representation of the digital word in
Latch A (0 ≤ D
A
≤ 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.
output voltage relationship for the circuit of Figure 17 with
R1 = R2.
+15V
–15V
V
DD
V
SS
AGND DGND
V
OUT
A
DAC A
AD7225*
V
REF
A
R2
V
OUT
R1
V
REF
R1, R2 = 10kΩ ± 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 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 0000
( )
REFREF
VV −=− 1
128
128