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DRV8350: Research before PCB DRV8350 Vs DRV8353

Nick Marsh50
Prodigy 130 points
Part Number: DRV8350
Other Parts Discussed in Thread: DRV8353

With a varying load, and without Hall effects,
What waveforms do we see on the backEMF function ?
Can someone point me to the correct graph ?

no Load, vs Half Load vs Full Load vs Overload..

The current sense Amplifiers, only give the winding resistance..
Is there any indication of the actual rotation positioning in the output of the sense amplifiers ?

  • 0
    TI__Guru 61280 points
    Nick,

    This is highly dependent on your motor choice, load, how much the load varies, etc. You will need to measure it experimentally.

    The current sense amplifiers are designed to measure the current through each phase of the motor. This is used for fault detection and user feedback, not for speed or position feedback.

    For output sensing of speed/position you will need an encoder or hall sensor coupled to the motor output.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 130 points

    of course I am looking to make a generic BLDC motor drive so there is no specific Motor

    I am looking toward a sensorless solution.

    Using the Current Sense amplifiers are on board the DRV8353.

    Please advise,

    I thought that if we had a constant load ( my starting point) we would not need the encoders.

    we would simply ramp up the PWM to the appropriate speed.

    I thought that you would be able to see a load change in the BackEMF. or excessive currents from the A/Ds Current Sense.

    I figured we could time delay the A/D reading to where we expect the peak to be. not sure how to check if its leading or lagging... maybe 8 samples in a row, find the peak drifting

    @3000RPM  with 6 poles 18000/60,  300 poles per second, 8 samples at TopDeadCenter, say 20degrees, 360/20 = 18% of arc

    @300hz 18% is 360/360 x 1/300 = 3.3mS   18% is 166uS  doing 8 samples is 20uS per sample... is 48Khz sampling achievable with low CPU overhead using DMA and interrupt control

    I guess its a lot easier to use the encoders...