Current feedback signal typical waveforms

AN4076

10/14

Doc ID 022923 Rev 1

3

Current feedback signal typical waveforms

Figure 5 shows some typical waveforms in the motor current electrical period timeframe:

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Channel 2 is the command for the low-side switch (turn-on signal low level)

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Channel 3 is the motor current feedback conditioned signal (at the op amp output)

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Channel 1 is the voltage on the shunt resistor

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Motor phase current is not reported but can be considered equal to the envelop of the

channel 3 waveform.

Figure 6 shows a particular of Figure 5 in a portion of the PWM period. It's possible to see

that voltage oscillations on the shunt resistor are bigger compared to the conditioned signal

and that the conditioned signal goes to its steady-state 1 µs later than the low-side turn-on

in the range of 100 W; a 2 µs range is, on the other hand, achievable if power is more in the

range of 1HP or higher.

Figure 5.

Typical waveform in the motor current electrical period timeframe