AD8223 Analog Devices, AD8223 Datasheet - Page 16

• Manufacturer Part Number: AD8223
• Description: Single Supply, Rail-to-Rail, Low Cost Instrumentation Amplifier
• Manufacturer: Analog Devices

AD8223
APPLICATIONS INFORMATION
BASIC CONNECTION
Figure 34 shows the basic connection circuit for the AD8223.
The +V
The supply can be either bipolar (V
single supply (−V
supplies should be capacitively decoupled close to the device’s
power pins. 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 35 shows how to create a differential output in-amp. A
OP1177
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.
S
op amp creates the inverted output. Because the op
and −V
+IN
–IN
Figure 35. Differential Output Using Op Amp
S
AD8223
S
terminals are connected to the power supply.
REF
= 0 V, +V
V
IN
R
20kΩ
20kΩ
G
S
= +3.0 V to +25 V). Power
A. DUAL SUPPLY
+
–
R
R
+V
G
G
–V
S
S
S
REF
OUTPUT
–
= ±2.5 V to ±12.5 V) or
+2.5V TO +6V
–2.5V TO –6V
OP1177
0.1µF
0.1µF
V
REF
+
+
+
10µF
10µF
+OUT
–OUT
V
REF (INPUT)
OUT
Figure 34. Basic Connections
Rev. PrA | Page 16 of 20
V
OUTPUT BUFFERING
The AD8223 is designed to drive loads of 10 kΩ or greater. If
the load is less than this value, the AD8223 output should be
buffered 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 Ω.
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 37 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.
IN
R
G
V
100Ω
IN
B. SINGLE SUPPLY
+
–
R
R
G
G
+V
R
G
S
REF
OUTPUT
–INPUT
+INPUT
Figure 37. Common-Mode Shield Driver
+3V TO +12V
AD8031
0.1µF
+
–
AD8223
Preliminary Technical Data
5V
Figure 36. Output Buffering
0.1µF
+
10µF
REF
R
R
2
2
G
G
V
REF (INPUT)
OUT
2
1
8
3
AD8223
+
–
OP113
–V
5V
4
+V
S
7
0.1µF
S
5
6
V
V
REFERENCE
OUT
OUT