An additional aspect to consider is that when current flows through the current-sensing resistor, power is

dissipated across this component. This dissipated power results in an increase in the internal temperature of the

package, including the integrated sensing resistor. This resistor self-heating effect results in an increase of the

resistor temperature helping to move the component out of the colder, wider drift temperature region.

8.3.3 Enhanced PWM Rejection Operation

The enhanced PWM rejection feature of the INA254 provides increased attenuation of large common-mode

ΔV/Δt transients. Large ΔV/Δt common-mode transients associated with PWM signals are employed in

applications such as motor or solenoid drive and switching power supplies. Traditionally, large ΔV/Δt common-

mode transitions are handled strictly by increasing the amplifier signal bandwidth, which can increase chip size,

complexity and ultimately cost. The INA254 is designed with high common-mode rejection techniques to reduce

large ΔV/Δt transients before the system is disturbed as a result of these large signals. The high AC CMRR, in

conjunction with signal bandwidth, allows the INA254 to provide minimal output transients and ringing compared

with standard circuit approaches.

8.3.4 Input Signal Bandwidth

The INA254 input signal, which represents the current being measured, is accurately measured with minimal

disturbance from large ΔV/Δt common-mode transients as previously described. For PWM signals typically

associated with motors, solenoids, and other switching applications, the current being monitored varies at a

significantly slower rate than the faster PWM frequency.

The INA254 bandwidth is defined by the –3-dB bandwidth of the current-sense amplifier inside the device. The

device bandwidth provides fast throughput and fast response required for the rapid detection and processing

of overcurrent events. Without the higher bandwidth, protection circuitry may not have adequate response time,

and damage may occur to the monitored application or circuit.

Figure 8-3 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 INA254 bandwidth.

Frequency (Hz)

0.01%

0.1%

1%

10%

1

10

100

1k

10k

100k

1M

D006

90% FS Input

Figure 8-3. Amplifier Performance Over Frequency

For applications requiring distortion sensitive signals, Figure 8-3 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 are required to determine the acceptance criteria, and to

validate the performance levels meet the system specifications.

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INA254

SLOS974 – JUNE 2021

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