Datasheet

®
INA111
7
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA111. Applications with noisy or high impedance
power supplies may require decoupling capacitors close to
the device 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 2Ω in series with the Ref pin will cause a typical
device with 90dB CMR to degrade to approximately 80dB
CMR (G = 1).
SETTING THE GAIN
Gain of the INA111 is set by connecting a single external
resistor, R
G
:
Commonly used gains and resistor values are shown in
Figure 1.
The 50kΩ term in equation 1 comes from the sum of the two
internal feedback resistors. These are on-chip metal film
resistors which are laser trimmed to accurate absolute val-
ues. The accuracy and temperature coefficient of these
resistors are included in the gain accuracy and drift specifi-
cations of the INA111.
The stability and temperature drift of the external gain
setting resistor, R
G
, also affects 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 can
make wiring resistance important. Sockets add to the wiring
resistance, which will contribute additional gain error (pos-
sibly an unstable gain error) in gains of approximately 100
or greater.
DYNAMIC PERFORMANCE
The typical performance curve “Gain vs Frequency” shows
that the INA111 achieves wide bandwidth over a wide range
of gain. This is due to the current-feedback topology of the
INA111. Settling time also remains excellent over wide
gains.
FIGURE 1. Basic Connections
DESIRED R
G
NEAREST 1% R
G
GAIN (Ω)(Ω)
1 No Connection No Connection
2 50.00k 49.9k
5 12.50k 12.4k
10 5.556k 5.62k
20 2.632k 2.61k
50 1.02k 1.02k
100 505.1 511
200 251.3 249
500 100.2 100
1000 50.05 49.9
2000 25.01 24.9
5000 10.00 10
10000 5.001 4.99
G = 1 +
50kΩ
R
G
(1)
A
1
A
2
A
3
6
10kΩ10kΩ
10kΩ10kΩ
7
4
3
8
1
2
V
IN
V
IN
R
G
V+
V–
INA111
G = 1 +
50kΩ
R
G
–
+
5
25kΩ
25kΩ
Load
V
O
= G • (V
IN
– V
IN
)
+
–
0.1µF
0.1µF
Pin numbers are
for DIP package.
+
–
V
O
INA111
R
G
Also drawn in simplified form:
V
O
Ref
V
IN
–
V
IN
+
Ref