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DRV8332: Driver overheating - PWM rate too fast?

Robbie Valentine86
Expert 1550 points
Part Number: DRV8332
Other Parts Discussed in Thread: DRV8320, DRV8323

Hello,

I'm using the DRV8332 BLDC motor driver IC from TI to drive a motor providing a torque of 1Nm (newton meter) at 600 rpm.  The windings of the motor are 30uH each.  I have a logic device up and running with a PI loop that drives the driver at a pwm rate of 97kHz.  The current draw from the power supply for this system is 24V at about 3.1A here.  The system can only run for 1-2min. before the drivers overheat.  We have the best heatsinks we can use per our volume so I don't have any wiggle room there.  I've noticed that another discrete motor driver that uses FETs with an Rdson of 8 mohms runs much cooler and doesn't overheat even at heavier loads.  I also noticed that this motor driver board runs its pwm rate much lower - 15kHz as opposed to my 97kHz. 

My questions are:

1. Could I be running my PWM too fast?  Is there an upper limit?

1a. If there is a value that is too high how does this come about.  How does one calculate this?

2. Does it sounds like the problem is mostly based on the difference in Rdson between the two power stages?  TI's chip is 80 miliohms and the other discrete FETs that run cooler are 8 mohms.

  • 0
    TI__Guru 61330 points
    Robbie,

    We are working on more concise thermal model calculators that could help with this exact question but those are not ready yet.

    What we can say is that we know that heat increases with the PWM rate as naturally the internals of the device need to switch at the much faster rate as you increase the PWM frequency.

    95kHz is quite high for most of our customers/applications. Is there a reason to run that high?

    As for an upper limit, it's hard to say, usually customers operate from 8kHz to 20kHz.

    If you would like a comparable device that uses external FETs, I'd suggest the DRV8320 or DRV8323. The 8323 includes three current sense amplifiers which can measure the phase currents independently for more precise feedback and control. The 8320 has no CSA if this is not needed. There is also an R variant which includes a Buck converter which can step down your VBUS to voltages for other board components such as the MCU.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    TI__Guru 61330 points
    Robbie,

    I will be closing this thread due to inactivity. Please ask a related question using the orange button at the top of the screen if your issue is not resolved.

    Regards,

    -Adam