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DRV8833: When the motor is blocked, nfault has no low-level output

Annie Liu
Genius 10295 points
Part Number: DRV8833

Hi Team,

The customer used DRV8833. He designed it according to specifications, and he used two H bridges in parallel design. Power-on test, it can rotate normally. He locked the motor and found that the nFault pin did not output low level. According to the formula Ichop=0.2/Risense, his resistance design is 0.2R, that is, 0.2/0.2=1A, and the measured stall current of the motor is 1.3A. 

According to the logic table of the specification, the nFault pin should have a low level output. There is no output from the test now. Customer would like to know what happened?

Thanks,

Annie

  • 0
    TI__Mastermind 37683 points

    Hi Annie,

    I think the customer might be confusing current regulation with over-current protection (OCP). The nFAULT pin is not pulled low when the device enters current regulation during start-up or stall unless the output current is above the minimum OCP threshold of 2A which in this case is not. OCP does not use the current sensing circuitry used for PWM control so it functions independently to the Risense resistors.

    You can point the customer to this FAQ to learn more about the differences between current regulation  and OCP.

    Is the customer wanting to disable the driver when the motor stalls? If so, I suggest reading section 3 of this appnote to look at an example of an external stall detection circuitry.