
INA326, INA327
SBOS222
8
www.ti.com
INA326
V
O
Filtered
V
O
6
G = 2(R
2
/R
1
)
f
O
= 1kHz
R
O
470
C
O(1)
0.22
μ
F
R
2
C
2(1)
7
V+
4
0.1
μ
F
V
–
5
Single-Supply Operation
IA
COMMON(2)
IA
COMMON(2)
INA326
R
1
R
1
V
IN
–
V
IN+
V
O
Filtered
V
O
6
2
1
8
3
G = 2(R
2
/R
1
)
f
O
= 1kHz
R
O
470
C
O(1)
0.22
μ
F
R
2
C
2(1)
7
+2.5V
4
0.1
μ
F
–
2.5V
5
Dual-Supply Operation
NOTE: (1) C
and C
combine to form a 2-pole response that is
–
3dB at 1kHz.
Each individual pole is at 1.5kHz. (2) Output voltage is referenced to IA
COMMON
(see text).
NOTE: (1) C
and C
combine to form a 2-pole response that is
–
3dB at 1kHz.
Each individual pole is at 1.5kHz. (2) Output voltage is referenced to IA
COMMON
(see text).
(3) Output pedestal required for measurement near zero (see Figure 5).
1
8
V
IN
–
V
IN+
2
3
(3)
DESIRED
GAIN
R
1
(
)
R
2
|| C
2
(
|| nF)
0.1
0.2
0.5
1
2
5
10
20
50
100
200
500
1000
2000
5000
10000
400k
400k
400k
400k
200k
80k
40k
20k
8k
4k
2k
2k
2k
2k
2k
2k
20k || 5
40k || 2.5
100k || 1
200k || 0.5
200k || 0.5
200k || 0.5
200k || 0.5
200k || 0.5
200k || 0.5
200k || 0.5
200k || 0.5
500k || 0.2
1M || 0.1
2M || 0.05
5M || 0.02
10M || 0.01
APPLICATIONS INFORMATION
Figure 1 shows the basic connections required for operation of
the INA326. A 0.1
μ
F capacitor, placed close to and across the
power supply pins is strongly recommended for highest accu-
racy. R
o
C
o
is an output filter that minimizes auto-correction
circuitry noise. This output filter may also serve as an anti-
aliasing filter ahead of an Analog-to-Digital (A/D) converter. It
is also optional based on desired precision.
The output reference terminal is taken at the low side of R
2
(IA
COMMON
).
The INA326 uses a unique internal topology to achieve excel-
lent common-mode rejection (CMR). Unlike conventional in-
strumentation amplifiers, CMR is not affected by resistance in
the reference connections or sockets. See
“
Inside the INA326
”
for further detail. To achieve best high-frequency CMR, mini-
mize capacitance on pins 1 and 8.
FIGURE 1. Basic Connections.
SETTING THE GAIN
The INA326 is a two-stage amplifier with each stage gain set
by R
1
and R
2
, respectively (see Figure 4,
“
inside the INA326",
for details.) Overall gain is described by the equation:
G
R
R
=
2
2
1
(1)
The stability and temperature drift of the external gain-setting
resistors will affect gain by an amount that can be directly
inferred from the gain equation (1).
Resistor values for commonly used gains are shown in
Figure 1. Gain-set resistor values for best performance are
different for +5V single-supply and for
±
2.5V dual-supply
operation. Optimum value for R
1
can be calculated by:
R
1
= V
IN, MAX
/12.5
μ
A
(2)
where R
1
must be no less than 2k
.
DESIRED
GAIN
R
1
(
)
R
2
|| C
2
(
|| nF)
0.1
0.2
0.5
1
2
5
10
20
50
100
200
500
1000
2000
5000
10000
400k
400k
400k
200k
100k
40k
20k
10k
4k
2k
2k
2k
2k
2k
2k
2k
20k || 5
40k || 2.5
100k || 1
100k || 1
100k || 1
100k || 1
100k || 1
100k || 1
100k || 1
100k || 1
200k || 0.5
500k || 0.2
1M || 0.1
2M || 0.05
5M || 0.02
10M || 0.01