Datasheet

A1
A2
Single-Pole Filter
Capacitor
+2.7 V to +18 V
5 kW5 kW
96 kW
R
L
PRE OUT
BUF IN
GND
OUT
IN–IN+ V+
Load
−16 V to +80 V
Supply
R
S
INA270
0.01 µF 0.1 µF
INA270-Q1, INA271-Q1
SBOS401B –JULY 2007–REVISED FEBRUARY 2010 www.ti.com
APPLICATION INFORMATION
Basic Connection
Figure 1 illustrates the basic connection of the INA270 and INA271. The input pins, IN+ and IN–, should be
connected as closely as possible to the shunt resistor to minimize any resistance in series with the shunt
resistance. Power-supply bypass capacitors are required for stability. Applications with noisy or high-impedance
power supplies may require additional decoupling capacitors to reject power-supply noise. Minimum bypass
capacitors of 0.01 mF and 0.1 mF in value should be placed close to the supply pins. Although not mandatory, an
additional 10-mF electrolytic capacitor placed in parallel with the other bypass capacitors may be useful in
applications with particularly noisy supplies.
Figure 1. INA270 Basic Connections
Power Supply
The input circuitry of the INA270 and INA271 can accurately measure beyond its power-supply voltage, V+. For
example, the V+ power supply can be 5 V, whereas the load power-supply voltage is up to 80 V. The output
voltage range of the OUT terminal, however, is limited by the voltages on the power-supply pin.
Selecting R
S
The value chosen for the shunt resistor, R
S
, depends on the application and is a compromise between
small-signal accuracy and maximum permissible voltage loss in the measurement line. High values of R
S
provide
better accuracy at lower currents by minimizing the effects of offset, while low values of R
S
minimize voltage loss
in the supply line. For most applications, best performance is attained with an R
S
value that provides a full-scale
shunt voltage range of 50 mV to 100 mV. Maximum input voltage for accurate measurements is (V
S
– 0.2)/Gain.
Transient Protection
The –16-V to 80-V common-mode range of the INA270 and INA271 is ideal for withstanding automotive fault
conditions ranging from 12-V battery reversal up to 80-V transients, since no additional protective components
are needed up to those levels. In the event that the INA270 and INA271 are exposed to transients on the inputs
in excess of their ratings, external transient absorption with semiconductor transient absorbers (zeners or
Transzorbs) are necessary.
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