Datasheet
AD8223
Rev. 0 | Page 17 of 20
APPLICATIONS INFORMATION
+2V TO +12V
REF (INPUT)
–2V TO –12V
REF
OUTPUT
+3V TO +24V
+
–
+
–
+
V
S
10µF0.1µF
10µF0.1µF
10µF0.1µF
+
+
V
OUT
+
R
G
R
G
R
G
V
IN
–V
S
REF (INPUT)
REF
OUTPUT
+
V
S
V
OUT
R
G
R
G
R
G
V
IN
A. DUAL SUPPLY B. SINGLE SUPPLY
06925-043
Figure 36. Basic Connections
BASIC CONNECTION
Figure 36 shows the basic connection circuit for the AD8223.
The +V
S
and −V
S
terminals are connected to the power supply.
The supply can be either bipolar (V
S
= ±2 V to ±12 V) or single
supply (−V
S
= 0 V, +V
S
= +3 V to +24 V). Power supplies should
be capacitively decoupled close to the power pins of the device.
For best results, use surface-mount 0.1 µF ceramic chip capacitors
and 10 µF electrolytic tantalum capacitors.
The input voltage, which can be either single-ended (tie either
−IN or +IN to ground) or differential, is amplified by the
programmed gain. The output signal appears as the voltage
difference between the output pin and the externally applied
voltage on the REF input.
DIFFERENTIAL OUTPUT
Figure 37 shows how to create a differential output in-amp. An
OP1177 op amp creates the inverted output. Because the op
amp drives the AD8223 reference pin, the AD8223 can still
ensure that the differential voltage is correct. Errors from the
op amp or mismatched resistors are common to both outputs
and are thus common mode. These common-mode errors
should be rejected by the next device in the signal chain.
+IN
–IN
REF
AD8223
V
REF
20kΩ
+–
OP1177
+OUT
–OUT
20kΩ
06925-044
Figure 37. Differential Output Using Op Amp
OUTPUT BUFFERING
The AD8223 is designed to drive loads of 10 k or greater. If
the load is less than this value, buffer the AD8223 output with a
precision single-supply op amp such as the OP113. This op amp
can swing from 0 V to 4 V on its output while driving a load as
small as 600 .
5
V
AD8223
REF
OP113
5V
V
OUT
+
–
0.1µF
0.1µF
+
–
V
IN
R
G
06925-045
Figure 38. Output Buffering
CABLES
Receiving from a Cable
In many applications, shielded cables are used to minimize
noise; for best CMR over frequency, the shield should be
properly driven. Figure 39 shows an active guard drive that
is configured to improve ac common-mode rejection by
bootstrapping the capacitances of input cable shields, thus
minimizing the capacitance mismatch between the inputs.
R
G
2
–INPUT
+INPUT
100Ω
AD8223
AD8031
REFERENCE
V
OUT
R
G
2
+V
S
–V
S
2
7
6
5
4
1
8
3
06925-046
Figure 39. Common-Mode Shield Driver