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DRV8801: The working principle of DRV8801 motor driver

Samil CETINKAYA
Prodigy 10 points
Part Number: DRV8801
Other Parts Discussed in Thread: DRV8800

Greetings everyone,

I am trying to use DRV8801 motor driver for my project. As I understand, the driver can be used in 2 different modes. One with setting the phase input as pwm and one with directly giving the inputs of driver namely phase enable mode1 mode2. My question is how the speed of the motor is adjusted in the second setting that does not have any pwm signal. Is it automatically set to a speed or are there any adjustments to set the speed of the rotor. Another question is about the rotation way of the rotor. It says that the rotor turns in clock wise direction in forward mode and counter clock wise in reverse but I could not understand the view. I mean that should I look the rotor shaft from behind or the other side?  Thanks in advance

Best Regards

Samil

  • +1
    TI__Mastermind 22790 points

    Hey Samil,

    I think the confusion comes from the datasheet being a single datasheet for DRV8800 and DRV8801.  The DRV8801 only really has one control mode as you describe with PWM on the ENABLE pin.  The tables show it as 0 or 1, but you should PWM the ENABLE pin to control the speed and keep PHASE as 0 or 1.  

    As you probably know, you can also change the motor supply voltage to change how fast the motor spins for a given PWM value as described in 9.2.2.1 Motor Voltage

    The MODE pins change the decay mode, you can read more about decay modes here:  https://www.ti.com/lit/an/slva321a/slva321a.pdf#page=1

    For your second question, the direction the motor spins will depend on which motor wire is connected to OUT+ and OUT- on the motor driver.  If you swap the leads, it will spin the opposite direction.  If your motor has the + and - sides labelled and you put the + into OUT+ and - into OUT-, the motor should spin clockwise as viewed from the load side, looking at the motor.  So look from the front, not from behind.  

    Regards,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 10 points

    Hey Jacob, 

    Your explanation cleared my confusion. Thank you very much :). 

    Best Regards.

    Samil

  • 0 in reply to Jacob Thompson
    Prodigy 10 points

    Hello Jacob,


    My final question is you stated that ENABLE pin should be on PWM but in the data sheet it states “Another technique is to use a speed/direction control scheme where ENABLE is connected to a GPIO output and the PHASE is pulse-width modulated. In this case, both direction and speed are controlled with a single signal. ENABLE is only used to disable the motor and stop all current flow.” on page 19. Am I misjudging the statement ? Thanks in advance

    Best Regards. 
    Samil

  • +1 in reply to Samil CETINKAYA
    TI__Mastermind 22790 points

    Hey Samil,

    Ahh I see, my bad.  That is correct, and this works by changing the PWM duty cycle where 50% is stopped.  Above 50% duty cycle it would spin one direction, and below 50% it would spin the other direction as described in 9.2.3.2 Pulse-Width Modulating PHASE.  This is because the signal will be HIGH (forward) more than it is LOW (reverse), so the motor will go forward.  

    Personally I find that control method confusing to program because you have to think of 0% as full speed one direction and 100% full speed the other direction, and still are using two GPIOs (a PWM and a digital ON/OFF for the enable), same as the other control method.  This would save you a pin if you always had the motor driver enabled when the driver was on and could just tie the enable pin to 3.3V with a pull up resistor.  

    Regards,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 10 points

    Hey Jacob, 

    Thanks for your time and efforts. Everything is clear right now.  Wish you the best. 

    Best Regards

    Samil