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DRV10866 Starting position of FG output

masahiko shimizu
Guru 11235 points
Other Parts Discussed in Thread: DRV10866

Hi,

My customer is using DRV10866.
He has a issue about Starting position of FG output.
He uses FG signal to confirm position motor.
and he say that "DRV10866 has 3 point of starting(occurring) position of FG signal".

Could you let me know mechanism of FG frequency generator in DRV10866, please?
Can customer use FG signal as position detector?

Best regards,
Shimizu

  • 0
    TI__Guru** 114905 points
    Hi Shimizu-san,

    Our experts have been notified and should reply soon.
  • 0 in reply to Rick Duncan
    Guru 11235 points

    Hi

    I add information and question.

    Please see the attached file.

    There is 3 type of FG signal rise.

    I think FG is generated by bemf.

    I think "detected Pin" is selected from in U,V,M from this waveform,

    and  It's different each time.

    Is this correct?　

    Thanks

    Shimizu

    DRV10866_FG_detect0925.xlsx

  • 0 in reply to masahiko shimizu
    TI__Expert 3010 points

    Hi Shimizu-san,

    That's correct, FG is aligned to commutation states of one of the three phases U-V-W. During low speed and startup it is held high until enough back emf is generated by motor

    Regards

    Krushal

  • 0 in reply to Krushal
    Guru 11235 points
    Hi Krushal-san,

    Thank you for your support.
    Please let a little more questions.

    Customer had many experiment.
    Customer tried input PWM operation as "L -> PWM ". and then, Selected phase for detection BEMF is fixed a certain one phase.

    So, We have the following questions.
    1.How is the one of three phases selected?
    　->Please tell me the chosen standard.
    2.When input PWM operates as "H(100%duty) -> PWM ", Are we able to specify the selected phase for detection BEMF?
    3.At customer experiment, Selected phase for detection BEMF was fixed a certain one phase.
    Is this accidental or Inevitable?

    Thanks
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Expert 3010 points

    Hi Shimizu-san,

    There is no fixed mechanism for selecting motor phase to align FG signal. It depends on starting position of motor. DRV10866 has blind start, so regardless of starting position it starts commuting. DRV109866 monitors zero crossing of all phases U-V-W and whenever speed of motor crosses minimum speed threshold, it activates FG signal. FG signal will be aligned to the first phase it detects minimum speed 

    Alignment of FG signal to particular phase is also not dependent on PWM signal. 

    Regards,

    Krushal 

  • 0 in reply to Krushal
    Guru 11235 points

    Hi Krushal-san,

    Thank you for your support.
    I add 2 question.

    1. You commented "FG signal will be aligned to the first phase it detects minimum speed" at previous post.
        How fast is "minimum speed"?

    2. By the becoming input PWM to low level(up to 500us), Is "BEMF detection phase" reset?

    ->At "7.4.1 Start-up" of datasheet, there is "At start-up with motor at standstill, commutation logic starts to drive the motor in open-loop with U-phase high, Vphase low, and the W-phase shut off"
    I think that "input low(up to 500us) at being over minimum speed" causes IC standby(BEMF detection phase reset) and fixed phase.

    Thanks
    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Expert 3010 points

    Hi Shimizu-san,

    Answer to

    1st question : Minimum speed is 18 Hz

    2nd question: needs more clarification. Can you elaborate more on what is customer is trying to achieve here

    Regards,

    Krushal

  • 0 in reply to Krushal
    Guru 11235 points

    Hi Krushal-san,

    Thank you for your support.

    About 2nd question,

    Customer would like to fix BEMF detect phase.
    Customer and I experimented to fix BEMF detect phase.

    At this experiment, we knew that BEMF detection phase is fixed by making input PWM low level at the moment in the middle of a certain or more motor operation speed.
    　
    We think the following.
    - Standby mode resets selection of detection phase
    - At being out standby mode by PWM low input under 500us, BEMF detection is run again.
    - BEMF detection starts from state1.
    - At state 1, Off pin is W phase. and then, BEMF detection phase becomes W phase.
    *Of cause, this is need on the following event
    - motor speed is over 18Hz
    - BEMF occurs certainly at W phase.

    Is detected phase reset by standby mode? 　　　　

    Thanks,
    Shimizu

  • 0 in reply to masahiko shimizu
    Guru 11235 points
    Hi Krushal-san,

    How is the progress?

    Thanks,
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Expert 3010 points

    Hi Shimizu-san,

    Sorry for delayed response 

    Alignment for FG signal to particular phase will reset when motor comes out of stand by mode. Every time motor is restarted after stand by mode, starting position of motor can change and BEMF detection changes. As per electrical spec on page 5 of datasheet, DRV109866 will enter standby when pulse on PWM pin is low for more than 500 uS

    Regards,

    Krushal