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DRV10974: Comparing sensorless BLDC startup for DRV11873 and DRV10974

Matt Darval
Prodigy 30 points
Part Number: DRV10974
Other Parts Discussed in Thread: DRV10975, , DRV11873

I'm looking into sensorless, brushless DC motor drivers with integrated drive FETs. I've been testing with the eval boards for the DRV11873, DRV10974, and DRV10975, trying to drive 3 similar motors.

The DRV11873 has the least options for tuning, but it works great for all 3 motors. Motor startup is fast and consistent. The DRV11873 uses trapezoidal drive as opposed to sinusoidal drive like the other two drivers. 

For the DRV10974, there are several resistor options for tuning. I've gone through the tuning procedure document and also a lot of trial and error. Even after that, none of the 3 motors will consistently start up. About 1 in 30 times the motors will fail to transition from the open loop to closed loop control on startup. The DRV11873 doesn't have the same, slow (1 to 2 seconds) startup ramping that the DRV10974 does. 

 

Besides sinusoidal drive, I'm wondering what the differences are that might be giving us trouble. Why do the DRV10974 and DRV10975 need to be fine tuned for a specific motor, vs. the DRV11873 which seems to just work fine without tuning. What advantages are there with the DRV10974 vs. the DRV11873? How much more efficient can we expect sinusoidal drive to be for a ~4W motor?

  • 0
    TI__Mastermind 18900 points
    Hey Matt,

    An expert has been notified and should be able to answer sometime Monday if.

    Generally speaking, it sounds like you have two questions: There's some tuning problems with the DRV10974/975 that I don't experience with the DRV11873, why is that? And what are the differences or pro's and con's between the two families.

    Can you share some information about the motor parameters and the system in the meantime? This includes Phase to Phase resistance, Phase to Phase Inductance, Kt in mV/Hz, and VCC of your system.

    Thanks,

    -Cole
  • 0 in reply to Cole Macias
    Prodigy 30 points

    Thanks Cole, good summary of the 2 questions:

    1) I'm struggling to tune with the DRV10974 and get reliable startup for all 3 motors, but the DRV11873 just works. Why is that?

    2) For our application, what are the reasons for using the DRV10974 over the DRV11873?

    Here's more information about the application.

    All 3 motors:

    • 12V motor voltage
    • 2000 to 3000 RPM speed range
    • 4W to 6W (333mA to 500mA) max electrical input power (at max motor mechanical load)
    • 9 slots and 12 poles (6 pole pairs), 3 to 1 ratio electrical to mechanical period  

    Motor 1:

    • 12.96 ohms phase to phase resistance (6.48 ohms per phase)
    • 4.47 mH phase to phase inductance (2.24 mH per phase)
    • Kt phase to phase = 47 mV/Hz (where1 Hz is the electrical period)
    • Best tuning values I've found: Rcs=38.3k (800mA), Radv = 71.5k (500us), Rrmp = 17.8k

    Motor 2:

    • 11.5 ohms phase to phase resistance (5.75 ohms per phase)
    • 2.63 mH phase to phase inductance (1.32 mH per phase)
    • Kt phase to phase = 29 mV/Hz (where1 Hz is the electrical period)
    • Best tuning values I've found: Rcs=25.5k (600mA), Radv = 49.9k (300us), Rrmp = 17.8k

    Motor 3:

    • 7.7 ohms phase to phase resistance (3.85 ohms per phase)
    • 1.93 mH phase to phase inductance (0.97 mH per phase)
    • Kt phase to phase = 38 mV/Hz (where1 Hz is the electrical period)
    • Best tuning values I've found: Rcs=25.5k (600mA), Radv = 71.5k (500us), Rrmp = 17.8k
  • 0 in reply to Matt Darval
    TI__Expert 6065 points

    Hey Matt,

    Q1) "I'm struggling to tune with the DRV10974 and get reliable startup for all 3 motors, but the DRV11873 just works. Why is that?"

    A1) DRV11873 is particularly tuned at a certain setting for fan motor drive applications. DRV10974 is for general motors, and needs to be tuned. The DRV10974 might not be working because of:

    a) The DRV11873's trapezoidal commutation scheme might work for your particular motors more reliably than DRV10974. 

    b) improper tuning, either by the user, or by the device when it's self tuning the Kt.

    Q2) For our application, what are the reasons for using the DRV10974 over the DRV11873?

    A2) To get a quick overview of DRV11873 vs DRV10974, please look at the comparison below from ti's product comparison tool. You can see for example from the table that you would use DRV10974 over DRV11873 if you wanted to control speed with an analog voltage instead of pwm.

    Note: If/when evaluating the DRV10975, which provides the most flexibility in tuning, I would recommend starting with this template conservative settings, and change the kt and resistance parameters in the settings for your specific motor.

    e2eTemplateSettings.csv