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INA191

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SLYS020A – FEBRUARY 2019 – REVISED APRIL 2019

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7.3 Feature Description

7.3.1 Precision Current Measurement

The INA191 provides accurate current measurements over a wide dynamic range. The high accuracy of the

device is attributable to the low gain error and offset specifications. The offset voltage of the INA191 is less than

Another advantage of low offset is the ability to use a lower-value shunt resistor that reduces the power loss in

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

The maximum gain error of the INA191 is specified to be within 0.25% for most gain options. As the sensed

voltage becomes much larger than the offset voltage, the gain error becomes the dominant source of error in the

current-sense measurement. When the device monitors 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 many current-sense amplifiers because this device offers very low input bias

current. The low input bias current of the INA191 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 at the inputs. For

these amplifiers, the input current is the result of the resistor network that sets the gain and additional current to

bias the input amplifier. 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 input filters to reject high-frequency noise before the

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

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

measurement accuracy of the INA191.

The third benefit of low bias current is the ability to use a larger current-sense resistor. This ability allows the

device to accurately monitor currents as low as 1 µA.

7.3.3 Low Quiescent Current With Output Enable

in most applications. The quiescent current of the INA191 is only 43 µA (typ), while providing a small-signal

portable electronic systems without 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. When in

the disabled state, the INA191 typically draws 10 nA of total supply current.