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DRV8301-EVM-HC Motor Startup Issue

Jeffery Pfarr
Genius 14317 points
Other Parts Discussed in Thread: DRV8301

Customer asks:

We are using the DRV8301-HC-EVM with Hercules RM46CNCD for initial motor control development work. Recently, my software guy Mike, ran into an issue with failing to spinning the BLDC using Hall Sensor feedback.

I took a look at the HW and see that he is commanding the PWM inputs to the DRV8301 properly, but the high side output drivers do not pass the charge pump voltage when on.  The charge pump is pumping and the GVDD rail is at 10V.  If we give the rotor a twist, the motor starts to spin and DRV8301 outputs are all as expected.

Based on this empirical data, I had Mike sequence the PWM inputs through a commutation cycle regardless of the hall sensor feedback, and viola, the motor starts every time.

I see nothing in the DRV8301 datasheet that suggests the high side drivers will not turn on until PWM sequencing starts. The low side drivers turn on... so it does not appear that the part is in a fault state.

Any idea what causes this behavior, and if it is expected?  For now, we will continue to kick-start the commutation... but I would like to understand why this is required.

  • 0
    TI__Mastermind 26065 points

    Hi Jeffery

    DRV8301 have both bootstrap and trickle boost for high side gates. Bootstap works with PWM and acts as the main predriver and trickle boost only for 100% PWM maintaining. trickle boost can only handle very small current, so you need PWM switching at first and charging the gate to full, then, trickle boost can maintain the ON state for high side FETs.

    From your description, it is recommended that doing the PWM at startup first. Small duty PWM startup is a very common practise for the BLDC not only for bootstrap but also to limit the startup current.

    Also could you show the schematic of DRV8301? because please make sure that you don't have the resistors between Gate and Source where the leak current will damp the function of trickle boost.

    Thanks

    Wilson Zuo

    Motor Applicaiton Team

     

  • 0 in reply to Wilson Zuo
    TI__Expert 8885 points

    Jeffery,

    Are you making sure that 3-phase connection sequence between Driver outputs and Motor inputs are correct based on your commutation logic for Hall-sensor input?

    I have seen many times that even with wrong connection motor does start-up after initial push as you mentioned but definitely this is not the efficient rotation.

    Out of six possible connections between driver output and motor, only one is right. I would suggest you to look into this aspect and validate it to make sure that there is some other reason for start-up issue. I have recently published blog on similar topic; you refer to below link for more detail.

    http://e2e.ti.com/blogs_/b/motordrivecontrol/archive/2013/12/20/generate-your-own-commutation-table-part-2.aspx

    Best Regards

    Milan