Datasheet

INA2128
8
SBOS035A
www.ti.com
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA2128. 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) terminals
(Ref
A
and Ref
B
) which are normally grounded. These must
be low-impedance connections to assure good common-
mode rejection. A resistance of 8Ω in series with a Ref pin
will cause a typical device to degrade to approximately
80dB CMR (G = 1).
The INA2128 has separate output sense feedback connec-
tions, Sense
A
and Sense
B
. These must be connected to their
respective output terminals for proper operation. The output
sense connection can be used to sense the output voltage
directly at the load for best accuracy.
SETTING THE GAIN
Gain of the INA2128 is set by connecting a single external
resistor, R
G
, connected as shown:
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, 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 INA2128.
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 in
gains of approximately 100 or greater.
DYNAMIC PERFORMANCE
The typical performance curve “Gain vs Frequency” shows
that despite its low quiescent current, the INA2128 achieves
wide bandwidth, even at high gain. This is due to its current-
feedback topology. Settling time also remains excellent at
high gain—see “Settling Time vs Gain.”
NOISE PERFORMANCE
The INA2128 provides very low noise in most applications.
Low frequency noise is approximately 0.2µV
PP
measured
from 0.1 to 10Hz (G ≥ 100). This provides dramatically
improved noise when compared to state-of-the-art chopper-
stabilized amplifiers.
G = 1+
50kΩ
R
G
(1)
FIGURE 1. Basic Connections.
DESIRED R
G
NEAREST 1% R
G
GAIN (Ω)(Ω)
1NC NC
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
NC: No Connection.
A
1
A
2
A
3
6
(11)
7 Sense
(10)
(12)
(13)
(14)
(16)
(15)
40kΩ40kΩ
40kΩ40kΩ
9
8
2
4
3
1
Pin numbers for
Channel B shown
in parentheses.
V
IN
V
IN
R
G
V+
V–
INA2128
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
NOTE: If channel is unused,
connect inputs to ground, sense
to V
O
, and leave Ref open-circuit.
+
–
V
O
R
G
Also drawn in simplified form:
INA2128
Ref
V
O
V
IN
–
V
IN
+
Ref