R

SHUNT

V

REF

V

OUT

V+

V

CM

R

< 10W

S

R

INT

R

< 10

S

W

R

INT

Load

C

F

Bias

INA210, INA211

INA212, INA213

INA214

SBOS437E – MAY 2008 – REVISED JUNE 2013

www.ti.com

UNIDIRECTIONAL OPERATION

Unidirectional operation allows the INA210-INA214 to measure currents through a resistive shunt in one

direction. The most frequent case of unidirectional operation sets the output at ground by connecting the REF pin

to ground. In unidirectional applications where the highest possible accuracy is desirable at very low inputs, bias

the REF pin to a convenient value above 50mV to get the device output swing into the linear range for zero

inputs.

A less frequent case of unipolar output biasing is to bias the output by connecting the REF pin to the supply; in

this case, the quiescent output for zero input is at quiescent supply. This configuration would only respond to

negative currents (inverted voltage polarity at the device input).

BIDIRECTIONAL OPERATION

Bidirectional operation allows the INA210-INA214 to measure currents through a resistive shunt in two directions.

In this case, the output can be set anywhere within the limits of what the reference inputs allow (that is, between

0V to V+). Typically, it is set at half-scale for equal range in both directions. In some cases, however, it is set at a

voltage other than half-scale when the bidirectional current is nonsymmetrical.

The quiescent output voltage is set by applying voltage to the reference input. Under zero differential input

conditions the output assumes the same voltage as is applied to the reference input.

INPUT FILTERING

An obvious and straightforward filtering location is at the device output. However, this location negates the

advantage of the low output impedance of the internal buffer. The only other filtering option is at the device input

pins. This location, though, does require consideration of the ±30% tolerance of the internal resistances.

Figure 24 shows a filter placed at the inputs pins.

Figure 24. Filter at Input Pins

The addition of external series resistance, however, creates an additional error in the measurement so the value

of these series resistors should be kept to 10

Ω or less if possible to reduce impact to accuracy.. The internal bias

network shown in Figure 24 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 at 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 resistor add to the measurement can be calculated using

Equation 2 where the gain error factor is calculated using Equation 1.

10

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