INT

F

INT

F

INT

1250 R

Gain Error Factor

(1250 R ) (1250 R

) (R

R

)

u

u

u

u

2.7 V to 5.5 V

Bias

IN±

IN+

VS

REF

OUT

INA181

Copyright © 2017, Texas Instruments Incorporated

+

±

Bus Voltage

±0.2 V to +26 V

Load

21

INA181, INA2181

www.ti.com

SBOS793A – APRIL 2017 – REVISED AUGUST 2017

Product Folder Links: INA181 INA2181

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Copyright © 2017, Texas Instruments Incorporated

Application Information (continued)

9.1.3 Signal Filtering

Provided that the INAx181 output is connected to a high impedance input, the best location to filter is at the

device output using a simple RC network from OUT to GND. Filtering at the output attenuates high-frequency

disturbances in the common-mode voltage, differential input signal, and INAx181 power-supply voltage. If filtering

at the output is not possible, or filtering of only the differential input signal is required, it is possible to apply a

filter at the input pins of the device. Figure 42 provides an example of how a filter can be used on the input pins

of the device.

Figure 42. Filter at Input Pins

The addition of external series resistance creates an additional error in the measurement; therefore, the value of

these series resistors must be kept to 10 Ω (or less, if possible) to reduce impact to accuracy. The internal bias

network shown in Figure 42 present at the input pins creates a mismatch in input bias currents when a

differential voltage is applied between the input pins. If additional external series filter resistors are added to the

circuit, the mismatch in bias currents results in a mismatch of voltage drops across the filter resistors. This

mismatch creates a differential error voltage that subtracts from the voltage developed across the shunt resistor.

This error results in a voltage at the device input pins that is different than the voltage developed across the

shunt resistor. Without the additional series resistance, the mismatch in input bias currents has little effect on

device operation. The amount of error these external filter resistors add to the measurement can be calculated

using Equation 6, where the gain error factor is calculated using Equation 5.

The amount of variance in the differential voltage present at the device input relative to the voltage developed at

as shown in Figure 42. The reduction of the shunt voltage reaching the device input pins appears as a gain error

when comparing the output voltage relative to the voltage across the shunt resistor. A factor can be calculated to

determine the amount of gain error that is introduced by the addition of external series resistance. Calculate the

expected deviation from the shunt voltage to what is measured at the device input pins is given using Equation 5:

where:

•

•

(5)