Frequency (Hz)

0.01%

0.1%

1%

10%

1

10

100

1k

10k

100k

1M

D006

90% FS Input

11

INA240

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SBOS662A – JULY 2016 – REVISED OCTOBER 2016

Product Folder Links: INA240

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Copyright © 2016, Texas Instruments Incorporated

Feature Description (continued)

Figure 23 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 23 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.

Figure 23. Performance Over Frequency

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.