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DRV8833 PWM Output Problem

Former Member
Former Member
Other Parts Discussed in Thread: DRV8833EVM, DRV8833

I am using the DRV8833EVM to drive two small DC motors from a LaunchPad. I provide a digital (HIGH or LOW) to xIN1 and a PWM value to xIN2 but the output to the motors seems to be responding incorrectly.

I used a logic analyzer to look at the lines during operation(connected at the DRV8833EVM) and the xINx lines appear to be behaving correctly. Although the datasheets says if you drive xIN1 HIGH that xOUT1 should also be driven HIGH. From what I can tell xOUT1 is being driven by the inverse of xIN1 (example during a high pulse the output is driven low and during a low pulse the output is high).

This behaviour is the opposite of what I am expecting and I am not sure why. Can anyone help clear this up?

  • 0
    TI__Mastermind 21305 points

    Hi Joshua,

    What you are seeing is related to how the Motor Drive does decay modes. When you stop driving the motor, current still flows since it is an inductor. The decay modes determine where the current is directed. You can check out page 8 of the datasheet for the truth tables.

    State 0/0 is Fast Decay. Both outputs are High Z.

    State 1/1 is Slow Decay. Both outputs are Low.

    Let me know if I misunderstood your questions or have additional ones.

  • 0 in reply to Nicholas Oborny
    TI__Mastermind 21305 points

    I am looking through your scope shot and see what you are saying. Is this the inverse you are seeing? Can you verify that your probes aren't mislabed/flipped, just trying to rule out simple things.

    BIN1    BIN2    BOUT1    BOUT2

    1          1         0             0

    1          0         0             1

  • Former Member
    0 Former Member in reply to Nicholas Oborny

    Hi Nick,

    Thank you for the quick response! But, that doesn't quite answer my question. And the table of inverses seems correct in some cases but not in all. Let me try to explain what I am seeing.

    Problem 1: When the DRV8833 is provided a short high pulse the output is driven low during the same time period. This means when I send it a short PWM wave expecting the motor to spin slowly the output is actually driving the motor almost full on. (You can see this is the first scope) Unfortunately, I thought the waves were flipped to, but the probes are correct I can retake them if you would like to see? (AIN1 and BIN1 are direction pins both being driven HIGH or LOW to drive both motors FWD or REV)

    Problem 2: In the second scope shot I am driving AIN1 and BIN1 with a direction (HIGH or LOW for FWD or REV) to drive to motors in opposite directions at the same speed with the same PWM. You will notice that the PWM pulse looks identical but the outputs are inverse meaning one motor is driven at full speed and progresses to zero speed while the second motor starts at zero speed and progress to full speed as the PWM pulse increases.

  • Former Member
    0 Former Member in reply to Former Member

    Ok so I did a final triple check of the signals. There was one mislabel which is BOUT1 is actually BOUT2 and BOUT2 is actually BOUT1. Got the two mixed up.