Datasheet

10
®
INA125
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA125. 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 instrumentation amplifier refer-
ence (IA
REF
) terminal which is normally grounded. This
must be a low impedance connection to assure good com-
mon-mode rejection. A resistance of 12Ω in series with the
IA
REF
pin will cause a typical device to degrade to approxi-
mately 80dB CMR (G = 4).
Connecting V
REF
OUT (pin 4) to one of the four available
reference voltage pins (V
REF
BG, V
REF
2.5, V
REF
5, or V
REF
10)
provides an accurate voltage source for bridge applications.
For example, in Figure 1 V
REF
OUT is connected to V
REF
10
thus supplying 10V to the bridge. It is recommended that
V
REF
OUT be connected to one of the reference voltage pins
even when the reference is not being utilized to avoid
saturating the reference amplifier. Driving the SLEEP pin
LOW puts the INA125 in a shutdown mode.
SETTING THE GAIN
Gain of the INA125 is set by connecting a single external
resistor, R
G
, between pins 8 and 9:
(1)
Commonly used gains and R
G
resistor values are shown in
Figure 1.
DESIRED GAIN R
G
NEAREST 1%
(V/V) (Ω)R
G
VALUE (Ω)
4NCNC
5 60k 60.4k
10 10k 10k
20 3750 3740
50 1304 1300
100 625 619
200 306 309
500 121 121
1000 60 60.4
2000 30 30.1
10000 6 6.04
NC: No Connection.
FIGURE 1. Basic Connections.
G =4+
60kΩ
R
G
A
1
Ref
Amp
10V
A
2
30kΩ
10kΩ
10kΩ
30kΩ
Bandgap
V
REF
13
12
1
14
15
16
4
6
9
10
11
IA
REF
V
O
5
8
7
R
G
Load
Sense
+
–
R
(2)
R
2R
4R
INA125
V
REF
COM
V
REF
BG
V
REF
2.5
V
REF
5
V
REF
10
V
REF
Out
V
IN
0.1µF
V+
+
V
IN
–
2
SLEEP
(1)
3
0.1µF
V–
V
O
= (V
IN
– V
IN
) G
G = 4 + 60kΩ
+–
R
G
NOTE: (1) SLEEP pin should be connected
to V+ if shutdown function is not being used.
(2) Nominal value of R is 21kΩ, ±25%.