Datasheet

+
20 kΩ 380 kΩ
380 kΩ
380 kΩ
19 kΩ
30 V
1 F
GND
4 7
2
3
1
6
5
−IN
+IN V
OUT
= (+IN) – (–IN) + V
REF
V
REF
100 nF
+
20 kΩ 380 kΩ
380 kΩ
380 kΩ
19 kΩ
−15 V
1 F
15 V
1 F
GND
4 7
2
3
1
6
5
−IN
+IN V
OUT
= (+IN) − (−IN)
100 nF100 nF
INA149
www.ti.com
SBOS579B SEPTEMBER 2011REVISED JULY 2012
APPLICATION INFORMATION
BASIC INFORMATION
Figure 43 shows the basic connections required for dual-supply operation. Applications with noisy or high-
impedance power-supply lines may require decoupling capacitors placed close to the device pins. The output
voltage is equal to the differential input voltage between pins 2 and 3. The common-mode input voltage is
rejected. Figure 44 shows the basic connections required for single-supply operation.
Figure 43. Basic Power and Signal Connections for Figure 44. Basic Power and Signal Connections for
Dual-Supply Operation Single-Supply Operation
TRANSFER FUNCTION
Most applications use the INA149 as a simple unity-gain difference amplifier. The transfer function is given in
Equation 1:
V
OUT
= (+IN) – (–IN) (1)
Some applications, however, apply voltages to the reference terminals (REF
A
and REF
B
). The complete transfer
function is given in Equation 2:
V
OUT
= (+IN) – (–IN) + 20 × REF
A
– 19 × REF
B
(2)
COMMON-MODE RANGE
The high common-mode range of the INA149 is achieved by dividing down the input signal with a high precision
resistor divider. This resistor divider brings both the positive input and the negative input within the input range of
the internal operational amplifier. This input range depends on the supply voltage of the INA149.
Both Figure 2 and Figure 3 can be used to determine the maximum common-mode range for a specific supply
voltage. The maximum common-mode range can also be calculated by ensuring that both the positive and the
negative input of the internal amplifier are within 1.5 V of the supply voltage.
In case the voltage at the inputs of the internal amplifier exceeds the supply voltage, the internal ESD diodes
start conducting current. This current must be limited to 10 mA to make sure not to exceed the absolute
maximum ratings for the device.
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