Datasheet

®
INA131
7
device. Absolute accuracy of the internal values is ±40%.
The nominal gain with an external R
G
resistor can be
calculated by:
G = 100 +
250 kΩ
R
G
Where: R
G
is the external gain resistor.
Accuracy of the 250kΩ term is ±40%.
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).
NOISE PERFORMANCE
The INA131 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
Amplifier may provide lower noise.
Low frequency noise of the INA131 is approximately
0.4µVp-p measured from 0.1 to 10Hz. This is approxi-
mately one-tenth the noise of state-of-the-art chopper-stabi-
lized amplifiers.
FIGURE 1. Basic Connections.
(1)
A
1
A
2
A
3
6
25kΩ5kΩ
25kΩ5kΩ
7
4
3
8
1
2
V
IN
V
IN
V+
V–
INA131
–
+
5
Over-Voltage
Protection
25kΩ
25kΩ
Over-Voltage
Protection
Load
V
O
= 100 • (V
IN
– V
IN
)
+
–
0.1µF
0.1µF
Pin numbers are
for DIP packages.
+
–
V
O
INA131
Also drawn in simplified form:
V
O
Ref
V
IN
–
V
IN
+
2.63kΩ
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA131. 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 device
with 110dB CMR to degrade to approximately 106dB CMR.
SETTING THE GAIN
No external resistors are required for G = 100. On-chip
laser-trimmed resistors set the gain, providing excellent gain
accuracy and temperature stability. Gain is distributed be-
tween the input and output stages of the INA131. Bandwidth
is increased by approximately five times (compared to the
INA114 in G = 100). Input common-mode range is also
improved (see “Input Common-Mode Range”).
Although the INA131 is primarily intended for fixed
G = 100 applications, the gain can be increased by connect-
ing an external resistor to the R
G
pins. The internal resistors
are trimmed for precise ratios, not to absolute values, so the
influence of an external resistor will vary from device to