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DRV8874: Motor working in different Pmode

Danny Jiang
Prodigy 10 points
Part Number: DRV8874

Tool/software:

1. When set Pmode = high，IN1=HIGH, IN2= PWM, so it works between forward and brake.

2. When set Pmode = low，PH =HIGH, EN = PWM, so it also works between forward and brake.

The 1&2 forward PWM duty is same. But the motor rotates more faster in 2 like lack of brake. why?

As my understanding, the motor works effect is should be almost same. 

We want to use Pmode low mode, but hope the motor can work slowly.

  • 0
    TI__Genius 11891 points

    Hi,

    Thanks for your question.

    My team mate will review the question and get back to you.

    Thanks,

    Ibinu

  • 0
    TI__Mastermind 19790 points

    Hi Danny,

    As you stated above, I believe that the motor should be spinning at the same speed no matter the mode selected, as long as the control sequence is the same. 

    Which current chopping mode is used (cycle-by-cycle or fixed off-time), and is it the same in both tests?

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 10 points

    Hi David,

    Thanks for your reply.

    The current chopping mode is same, 20k resistor connected between IMODE and GND. And I think the working current is much smaller than Itrip.

    And there is another working mode(as below)

    3. Set Pmode = high，IN2=LOW, IN1= PWM, so it works between forward and COAST.

    It seems like the 2&3 much similar, both rotates faster than 1. So I'm confused.

  • 0 in reply to Danny Jiang
    TI__Mastermind 19790 points

    Hi Danny,

    The difference between the control modes should not change the speed of the motor. I would probe the inputs and output to see the signals going into the device while observing the output behavior. If possible, can you take some scope shots of inputs and output with and without a load. As long as the signals are the same going into the device there should be no change in the output behavior. 

    Best,

    David