Figure 8-1 shows the performance profile of the device over frequency. Harmonic distortion increases at the

upper end of the amplifier bandwidth with no adverse change in detection of overcurrent events. However,

increased distortion at the highest frequencies must be considered when the measured current bandwidth

begins to approach the INA240 bandwidth.

For applications requiring distortion sensitive signals, Figure 8-1 provides information to show that there is

an optimal frequency performance range for the amplifier. The full amplifier bandwidth is always available for

fast overcurrent events at the same time that the lower frequency signals are amplified at a low distortion

level. The output signal accuracy is reduced for frequencies closer to the maximum bandwidth. Individual

requirements determine the acceptable limits of distortion for high-frequency, current-sensing applications.

Testing and evaluation in the end application or circuit is required to determine the acceptance criteria and

to validate the performance levels meet the system specifications.

Frequency (Hz)

0.01%

0.1%

1%

10%

1

10

100

1k

10k

100k

1M

D006

90% FS Input

Figure 8-1. Performance Over Frequency

8.3.2 Selecting the Sense Resistor (RSENSE)

The INA240 determines the current magnitude from measuring the differential voltage developed across a

resistor. This resistor is referred to as a current-sensing resistor or a current-shunt resistor. The flexible design of

the device allows a wide input signal range across this current-sensing resistor.

The current-sensing resistor is ideally chosen solely based on the full-scale current to be measured, the

full-scale input range of the circuitry following the device, and the device gain selected. The minimum current-

sensing resistor is a design-based decision in order to maximize the input range of the signal chain circuitry.

Full-scale output signals that are not maximized to the full input range of the system circuitry limit the ability of

the system to exercise the full dynamic range of system control.

Two important factors to consider when finalizing the current-sensing resistor value are: the required current

measurement accuracy and the maximum power dissipation across the resistor. A larger resistor voltage

provides for a more accurate measurement, but increases the power dissipation in the resistor. The increased

power dissipation generates heat, which reduces the sense resistor accuracy because of the temperature

coefficient. The voltage signal measurement uncertainty is reduced when the input signal gets larger because

any fixed errors become a smaller percentage of the measured signal. The design trade-off to improve

measurement accuracy increases the current-sensing resistor value. The increased resistance value results

in an increased power dissipation in the system which can additionally decrease the overall system accuracy.

Based on these relationships, the measurement accuracy is inversely proportional to both the resistance value

and power dissipation contributed by the current-shunt selection.

By increasing the current-shunt resistor, the differential voltage is increased across the resistor. Larger input

differential voltages require a smaller amplifier gain to achieve a full-scale amplifier output voltage. Smaller

current-shunt resistors are desired but require large amplifier gain settings. The larger gain settings often have

increased error and noise parameters, which are not attractive for precision designs. Historically, the design

goals for high-performance measurements forced designers to accept selecting larger current-sense resistors

and the lower gain amplifier settings. The INA240 provides 100-V/V and 200-V/V gain options that offer the

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INA240

SBOS662C – JULY 2016 – REVISED DECEMBER 2021

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Product Folder Links: INA240