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INA191

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SLYS020 – FEBRUARY 2019

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7.3 Feature Description

7.3.1 Precision Current Measurement

Featuring both low offset and small gain error, the INA191 is capable of accurately measuring currents over a

wider range of currents while using the same current-sense resistor. The offset voltage of the INA191 is less than

15 µV. The low offset allows the device to be used in applications that measure current over a wide dynamic

range. In this case, the low offset improves the accuracy when the sensed currents are on the low end of the

measurement range. Another advantage of low offset is the ability to use a lower-value shunt resistor, which

reduces the power loss in the current-sense circuit, and improves the power efficiency of the end application.

The gain error of the INA191 is specified to be within 0.3% of the actual value. As the sensed voltage becomes

much larger than the offset voltage, the sensed voltage becomes the dominant source of error in the current-

sense measurement. When the device is monitoring currents near the full-scale output range, the total

measurement error approaches the value of the gain error.

7.3.2 Low Input Bias Current

The INA191 is different from most current-sense amplifiers in that this device offers very low input bias current.

The low input bias current of the INA191 (0.5 nA, typically) has three primary benefits.

The first benefit is the reduction of the current consumed by the device in both the enabled and disabled states.

Classical current-sense amplifier topologies typically consume tens of microamps of current in the resistor divider

network that determines the gain. To reduce the bias current to near zero, the INA191 uses a capacitively

coupled amplifier on the input stage, followed by a difference amplifier on the output stage.

The second benefit of low bias current is the ability to use a larger current-sense resistor, which allows the

device to accurately monitor currents as low as 1 µA.

The third benefit of low bias current is the ability to use input filters to reject high-frequency noise before the

signal is amplified. In a traditional current-sense amplifier, the addition of input filters comes with the price of

reduced accuracy; however, as a result of the low bias currents, input filters have little effect on the

measurement accuracy of the INA191.

7.3.3 Low Quiescent Current With Output Enable

in most applications. The quiescent current of the INA191 is only 45 µA (typ), while providing a small-signal

portable electronic systems without concern of excessive drain on the battery. Because many applications only

need to periodically monitor current, the INA191 features an enable pin that turns off the device until needed.

7.3.4 High-Side and Low-Side Current Sensing

The INA191 supports input common-mode voltages from –0.2 V to +40 V. Because of the internal topology, the

allows the INA191 to be used in high-side, as well as low-side, current-sensing applications, as shown in

Figure 1.