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Driver selection for BLDC application

David Wang60
Intellectual 980 points
Other Parts Discussed in Thread: INSTASPIN-BLDC, DRV8303, DRV8305

I have maxon flat motor EC90 (Part number: 244879) BLDC being used for a AUV application. It runs at 48V, with a nominal speed = 1610RPM, nominal torque = 533mNm, and nominal current = 2.27V. It is a sensored BLDC. Could you suggest solutions that would be appropriate for this type of motor and application?


I have been looking at the DRV8303 but I'm not quite sure what kind of controller is necessary for this. Is INSTASPIN-BLDC necessary? Ultimately, we need to control the speed of the motor based on our guidance/navigation control system.


THanks

-David

  • 0
    TI__Expert 4650 points
    Hi David,

    The DRV8303 would work for your motor. This driver does not require InstaSPIN and can be controlled using any microcontroller that can communicate over SPI and supply the required PWM inputs on the IN_X pins. Maximum logic voltage with this device is 7-V, so any controller that operates below this threshold will work.
  • 0 in reply to Phil Beard
    Intellectual 980 points

    As far as the PWN inputs, do I just need to supply it a continuous PWM at specific frequency with duty cycle that corresponds to how fast I need the motor to spin? I assume the DRV8303 takes in the continuous PWM, and has the control logic to determine the appropriate timing of the switching for 3-phase BLDC? Can all 6 PWM inputs be driven with one PWM output from a MCU, if we independently buffer the signal for each 6 inputs?

    Also, since the DRV8303 does have inputs for the sensors on the motor, what kind of effect would it have on the operation of the motor when sensorless?

    What would you recommend if we decide to use the sensors?

    Thanks

    -David

  • 0 in reply to David Wang60
    TI__Expert 4650 points
    Hi David,

    The DRV8303 does not have any internal commutation logic, meaning the external controller must interpret either the back-emf in each motor phase or use hall sensors to determine the proper IN_X PWM signals. The MCU must supply either 6 or 3 PWM signals depending on the operating mode of the device.

    The DRV8303 does not have inputs for sensors on the motor, let me know if you'd like me to clarify any pin functionalities with this device.

    If you decide to use hall sensors with this device you would just need to change the external MCU software. The DRV8303 just responds to the PWM signals on each IN_X Pin, so the rotor sensing method is independent to the driver.

    Page 23 of the DRV8303 datasheet shows how a sensorless solution could be implemented with this device.
  • 0 in reply to Phil Beard
    Intellectual 980 points
    ok I understand now, I was confused on the terminology between integrated and pre-driver. Some of the integrated drivers have the controllers (ie: DRV10x) versus some that don't but have FETs.

    Also, on some of the datasheets (ie: DRV8305) that says it has 1.25V and 1A peak gate drive currents. How exactly would the gates of the FETs experience that amount of peak current, especially if you limit it with a series resistor? If you don't have the series resistor, then I am assuming the peak current is probably some kind of transient effect when driving PWM signal?

    Thanks
    -David
  • 0 in reply to David Wang60
    TI__Expert 4650 points
    Hi David,

    If you were to add a series resistor this would limit the current available to the MOSFET gate. However, with the DRV8305 we offer a feature called IDRIVE that allows you to vary the source / sink current of the gate driver. For this device gate resistors are often not needed if the IDRIVE settings are acceptable for your application.

    Peak current is the maximum source or sink current applied to the MOSFET gate during turn on and turn off transitions. This will control how quickly the external MOSFETs can slew. We have an application note linked below if you're interested in reading more about this:

    www.ti.com/.../slva714a.pdf
  • 0 in reply to Phil Beard
    Intellectual 980 points
    great, thanks for the explanation.