Datasheet

®
INA114
8
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA114. 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 5Ω in series with the Ref pin will cause a typical
device to degrade to approximately 80dB CMR (G = 1).
SETTING THE GAIN
Gain of the INA114 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-
FIGURE 1. Basic Connections.
G = 1 +
50 kΩ
R
G
(1)
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
ues. The accuracy and temperature coefficient of these
resistors are included in the gain accuracy and drift specifi-
cations of the INA114.
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 (possi-
bly an unstable gain error) in gains of approximately 100 or
greater.
NOISE PERFORMANCE
The INA114 provides very low noise in most applications.
For differential source impedances less than 1kΩ, the INA103
may provide lower noise. For source impedances greater
than 50kΩ, the INA111 FET-input instrumentation ampli-
fier may provide lower noise.
Low frequency noise of the INA114 is approximately
0.4µVp-p measured from 0.1 to 10Hz. This is approximately
one-tenth the noise of “low noise” chopper-stabilized ampli-
fiers.
A
1
A
2
A
3
6
25kΩ25kΩ
25kΩ25kΩ
7
4
3
8
1
2
V
IN
V
IN
R
G
V+
V–
INA114
G = 1 +
50kΩ
R
G
–
+
5
Over-Voltage
Protection
25kΩ
25kΩ
Over-Voltage
Protection
Load
V
O
= G • (V
IN
– V
IN
)
+
–
0.1µF
0.1µF
Pin numbers are
for DIP packages.
+
–
V
O
INA114
R
G
Also drawn in simplified form:
V
O
Ref
V
IN
–
V
IN
+