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Original question:

DRV8874-Q1: Current overcurrent protection issue

DRV8874-Q1: DRV8874-Q1

Lance Kasari
Prodigy 10 points
Part Number: DRV8874-Q1
Other Parts Discussed in Thread: DRV8874, DRV8243-Q1, , DRV8873-Q1

I'm having a problem using the DRV8874 with a 775 DC Brushed motor, which recommends a startup current of 10A.

Setup: PMODE grounded (PH/EN mode), IMODE Grounded (Fixed off time, Auto retry), IPROPI = Shorted to ground (Current regulation disabled).

Two questions.

First off, it appears that low PWM frequencies of 1kHz or below cause the driver to go into over current protection and won't let the motor spin up. Likewise, setting EN from low to High without any acceleration does not allow the motor to spin up. The only way I can get the motor to spin up is by starting off with EN low, then setting the PWM to 0% with a frequency of 12kHz or greater and ramping up the PWM percentage to 100% over a few seconds. Is there something I'm doing wrong with my setup? Should the DRV8874 be able to start up the motor from zero by just switching EN to high?  I have Ipropi grounded and VRef set to 3V in order to disable any current regulation, but I think the over current is where the problem is. 

Second, the controller my client is using does not allow for a PWM frequency of over 1kHz. Can the DRV8874 work with a low frequency PWM? Should I be looking at a different driver?

Thanks,

Lance

  • 0
    TI__Mastermind 24855 points

    Hi Lance,

    I noticed that customer's driving condition is 10A(with a few second?) to ramp up. DRV8874-Q1 is not good device for this load profile. I recommend to move to DRV8243-Q1.

    DRV8874-Q1 OCP is 6A min. DRV8243-Q1 is OCP min 12A.

    PWM lower frequency(1KHz) is OK for both DRV8874-Q1 and DRV8243-Q1. DRV8243/44/45-Q1 is new generation line up. 

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    Prodigy 10 points

    Thank you for your reply. The motor normal runs at less than 2A at full speed. It is only during start up that it pulls higher current. I will take a look at the DRV8243, but are you saying that even for a short time at startup, the DRV8874 won't handle anything over 6A?  I only need to get the motor up to full speed without the OCP kicking in. Thanks.

  • 0 in reply to Lance Kasari
    Prodigy 10 points

    It looks to me that the problem with low frequency PWM, such as 500Hz, is that the current draw for this motor is high enough during the 1mS pulse to engage the OCP circuits, thereby not allowing the motor to spin up. At higher frequency PWM, the current doesn't go high enough or fast enough to engage the OCP. Does this sound plausible? How fast is the OCP circuit? I found that I needed to run the PWM at 10Khz or higher to get the motor to run.

  • 0 in reply to Lance Kasari
    TI__Mastermind 24855 points

    Hi Lance,

    DRV8874-Q1 OCP min is 6A. So DRV8874-Q1 cannot handle more than 6A even short duration.

    Deglitch time 3us.

    With lower PWM frequency, peak current my be higher. Anyway, motor current is more than 6A, DRV8873-Q1 is not good one.

    Another option is to use current regulation/ITRIP to reduce peak current. 

    regards

    Shinya Morita