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Unexpected DRV8332 shutdown

Johan Stenström
Intellectual 605 points
Other Parts Discussed in Thread: DRV8332, DRV8412

Hi,

We’re using DRV8332 drivers to drive several BLDC in our system. On one of the axes we experience strange driver behavior when trying to accelerate past a certain speed.

The first figure below shows the three phase current measurements along with the FAULTn signal (brown). The motor spins with 4900 rpm before the acceleration starts at around -0.3 s in the figure. As you can see the driver shuts the output down at 0 s, but without signaling any fault condition.

Since the motor continues to spin it will continue to commutate and seemingly resume drive. Because of high gain the controller will have increased the duty cycle so the driver soon shuts down again. But FAULTn is not asserted until around 0,25 s.

Another test run is seen in the figure below. It shows one phase current (red) zoomed in. It seems like the phase is shut down (at -20 ms) for 120 degrees during its Low Side ON state, still no fault condition (brown).

We use trapezoidal control according to the TI DRV8312EVM sensored example code (hard chop). The driver is set to Over Current Latching mode.

My question is, why does the driver shut down? And why doesn’t it signal any fault condition?

Best Regards,
Johan

  • 0
    TI__Mastermind 26065 points

    Hi Johan

    Could you also give the partly schematic for DRV8332? also it is not easy to find out the current level on your waveform, could you help to give something like 1V = ?A, also your mode setting and current limit settings?

    is your device get hot at the issue time?

    Thanks

    Wilson Zuo 

  • 0 in reply to Wilson Zuo
    Intellectual 605 points

    Hi Wilson,

    Thanks for your attention!

    The design follows the TI reference design: 1602.servo.pdf. The current plots are offset by -1,65 V and the relation should be 5,2A/1V.

    The driver is set to OC latching mode and the OC adjustment resistor is set to 30kOhm.

    The device doesn't get hot.

    Best Regards,
    Johan

  • 0 in reply to Wilson Zuo
    Intellectual 605 points

    Hi,

    We have determined that the shutdown was due to insufficient bootstrapping. The voltage was to low to open the high side switch at the commutation point where going from phase off to phase driving.

    We solved it by manually opening the low side switch a few cycles before opening the high side.

    I think the datasheet is lacking when it comes to describing the BST functionality and related shutdown! Also, I wonder if it could be driven externally like discussed in http://e2e.ti.com/support/applications/motor_drivers/f/38/t/273205.aspx for DRV8412? The referred application note seems to be missing.

    Best Regards,
    Johan

  • 0 in reply to Johan Stenström
    TI__Mastermind 21320 points

    Hi Johan,

    I do believe a similar setup could be used as discussed in that thread but would require experimentation. The app notes is still in progress unfortunately and not available yet.

    I will make a note to have the datasheet looked at.