7.3 Feature Description

7.3.1 Precision Current Measurement

The INAx191 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 INAx191 is less than

12 µV. In this case, the low offset improves the accuracy at light loads when VIN+ approaches VIN–.

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 INAx191 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 INAx191 is different from many current-sense amplifiers because this device offers very low input bias

current. The low input bias current of the INAx191 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 INAx191 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 INAx191.

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

The device features low quiescent current (IQ), while still providing sufficient small-signal bandwidth to be usable

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

bandwidth of 35 kHz in a gain of 100. The low IQ and good bandwidth allow the device to be used in many

portable electronic systems without excessive drain on the battery. Because many applications only need to

periodically monitor current, the INAx191 features an enable pin for each output that turns off the device until

needed. When in the disabled state, the INAx191 typically draws 10 nA of total supply current per channel.

7.3.4 Bidirectional Current Monitoring (INA2191 Only)

The INA2191 can sense current flow through a sense resistor in both directions. The bidirectional current-

sensing capability is achieved by applying a voltage at the REF pin to offset the desired output voltage. A

positive differential voltage sensed at the inputs results in an output voltage that is greater than the applied

reference voltage. Likewise, a negative differential voltage at the inputs results in output voltage that is less than

the applied reference voltage. The output voltage of the current-sense amplifier is shown in Equation 1. Equation

variables such as VOUT are valid for either VOUT1 or VOUT2 depending on which channel used.

OUT

LOAD

SENSE

REF

V

I

R

GAIN

V

u

u

(1)

where

• ILOAD is the load current to be monitored.

• RSENSE is the current-sense resistor.

• GAIN is the gain option of the selected device.

• VREF is the voltage applied to the REF pin.

INA191, INA2191

SLYS020C – FEBRUARY 2019 – REVISED AUGUST 2021

www.ti.com

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