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0:49 · With sound

Sense position

Low side, high side or in line: where should a motor drive sense current?

Read Note 19

Transcript

Three places to sense motor current.

Which one is best?

High side catches a phase shorted to ground.

But its current sense amp sits at 48 V.

And it only sees current while the top FET is on.

The amp needs time to settle after every switch.

With moteus-c1's amp at 30 kHz, that's 3 µs of each cycle.

So no phase can sit at 0 V, and the motor gets at most 44 V.

In line sees the current all the time, so there's no voltage cap.

But its current sense amp jumps 48 V every switch.

Low side is the cheapest. Its current sense amp sits at ground.

But it only sees current while the bottom FET is on.

So no phase can sit at 48 V, and the motor gets at most 44 V too.