Datasheet
®
7
INA116
APPLICATIONS INFORMATION
Figure 1 shows the connections required for basic operation
of the INA116. Applications with noisy or high impedance
power supplies may require decoupling capacitors close to
the supply pins as shown.
The output is referred to the output reference (Ref) terminal
which is normally grounded. This must be a low impedance
connection to assure good common-mode rejection. A resis-
tance of 30Ω in series with this connection will cause a
typical device to degrade to approximately 72dB CMR at
G = 1.
SETTING THE GAIN
Gain of the INA116 is set by connecting a single external
resistor, R
G
, as shown. The gain is—
Commonly used gains and resistor values are shown in
Figure 1.
The 50kΩ term in equation 1 is the sum of the two feedback
resistors of A
1
and A
2
. These on-chip metal film resistors are
laser trimmed to accurate absolute values. The accuracy and
temperature coefficient of these resistors are included in the
gain accuracy and drift specifications of the INA116.
The stability and temperature drift of R
G
also affect gain.
R
G
’s contribution to gain accuracy and drift can be directly
inferred from the gain equation (1). Low resistor values
required for high gain make wiring resistance important.
Sockets add to the wiring resistance that will contribute
additional gain error in gains of approximately 100 or
greater.
OFFSET TRIMMING
The INA116 is laser trimmed for low offset voltage and
offset voltage drift; most applications require no external
offset adjustment. Figure 2 shows an optional circuit for
trimming the output offset voltage. A voltage applied to the
Ref terminal is summed at the output. Op amp A
1
provides
a low source impedance for the Ref terminal, assuring good
common-mode rejection.
G =1+
50kΩ
R
G
(1)
FIGURE 1. Basic Connections.
INA116
R
G
Also drawn in simplified form:
V
O
Ref
V
IN
–
V
IN
+
A
1
A
2
A
3
R
4
60kΩ
R
3
60kΩ
R
2
60kΩ
R
1
60kΩ
V
IN
V
IN
R
G
V–
INA116
V
O
Ref
G = 1 +
50kΩ
R
G
–
+
R
FB
25kΩ
R
FB
25kΩ
+1
+1
Over-Voltage
Protection
Over-Voltage
Protection
4
3
2
1
16
5
6
7
8
11
9
13
Input Guards
See Text.
0.1µF
V+
0.1µF
DESIRED
GAIN
1
2
5
10
20
50
100
200
500
1000
2000
5000
10000
NC: No Connection.
R
G
(Ω)
NC
50.00k
12.50k
5.556k
2.632k
1.02k
505.1
251.3
100.2
50.05
25.01
10.00
5.001
NEAREST 1% R
G
(Ω)
NC
49.9k
12.4k
5.62k
2.61k
1.02k
511
249
100
49.9
24.9
10
4.99