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DRV8312 commutation scheme

Johan Stenström
Intellectual 605 points
Other Parts Discussed in Thread: DRV8312, CONTROLSUITE

Hi, 

I have a question about Figure 11 in the DRV8312 datasheet. How come in eg. S1 at 75 percent it alternates between driving A to B and B to A? I'VE also noticed that the same scheme isn't utilized in the BLDC Sensored project (DRV8312-C2-KIT). Why not? 

Best Regards, Johan 

  • 0
    TI__Guru** 119510 points

    Fig 11 is correct.

    Is your question on the 2nd column of S1?  PWM_A, B, and C are the high-side transistors, and the low-side are automatically getting the low-side IF THE phase is active.

    C is not-active (note that RESET is low), so all current must flow between A and B.

    So when A is HIGH, B must be low (and at the same time the A_lowside is LOW and B_lowside is HIGHT), and when B is HIGH, A must be low (not accounting for switching dead-time).

     

     

  • 0 in reply to ChrisClearman
    Intellectual 605 points

    Yes, it's the 2nd column of S1 that my question regards.

    Maybe there's something I'm missing but wouldn't driving from B to A at 25% counteract the motion you want to achieve? The code in f2803xbldcpwm_BLDC.h instead switches the RESET signal which would lead to at 25% of the time in S1 only B_lowside is open and no phase is driven. Could you please explain the differences between the two schemes?

  • 0 in reply to Johan Stenström
    TI__Guru** 119510 points

    this is the diference between a hard chop and a soft chop technique, as discussed on page 6 in the guide

    C:\ti\controlSUITE\development_kits\DRV8312-C2-KIT_v128\BLDC_Sensorless\~Docs\Sensorless Trapezoidal Control of BLDC Motors.pdf