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DRV8873H-Q1EVM: Overcurrent protection issue

Cherry Zhou
Mastermind 22235 points
Part Number: DRV8873H-Q1EVM
Other Parts Discussed in Thread: DRV8873

Hi team,

Here's some questions form the customer may need your help:

In hardware mode:

1. What is the minimum PWM duty cycle for the pwm control of 19KHZ to work properly? (Consider the effect of input and output delay)

2. The IPROPI pin resistance does not set the output maximum current, but simply provides a voltage variation of current? It's different from drv8873.

3. Enable the ITRIP feature via the nITRIP pin, maximum current setting of 6.5 A, 6.5 A has started protection, will 10 A overcurrent protection not be achieved? The OCP no longer works.

4. After OCP overcurrent protection, the output is turned off. Can I automatically restart? The motor starts with an inrush current of 12 A, the overcurrent protection shutdown output on start-up, will it fail to start?

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Mastermind 37683 points

    Hi Cherry,

    Cherry Zhou said:
    1. What is the minimum PWM duty cycle for the pwm control of 19KHZ to work properly? (Consider the effect of input and output delay)

    minimum and maximum duty cycle will be dependent on the dead time and slew rate. Assuming slew rate is 53.2V/µs at 13.5V (rise/fall time = 260ns). Dead time is equal to 500ns. The absolute minimum OFF pulse time is equal to Dead time + rise time + fall time = 260ns+500ns+500ns=1.26µs. You can estimate the minimum duty cycle at 19kHz  with this information.

    Cherry Zhou said:
    2. The IPROPI pin resistance does not set the output maximum current, but simply provides a voltage variation of current? It's different from drv8873.

    Correct. The IPROPI resistor only adjust the current range than can be monitored. The current regulation is set to 6.5A for the -H variant.

    Cherry Zhou said:
    3. Enable the ITRIP feature via the nITRIP pin, maximum current setting of 6.5 A, 6.5 A has started protection, will 10 A overcurrent protection not be achieved? The OCP no longer works.

    The device will try to regulate to 6.5A but in the case of a hard short (VM to GND for example), the driver won't be able to regulate this large current and so OCP will protect the device if current goes above 10-A.

    Cherry Zhou said:
    4. After OCP overcurrent protection, the output is turned off. Can I automatically restart? The motor starts with an inrush current of 12 A, the overcurrent protection shutdown output on start-up, will it fail to start?

    NO. the outputs will remain off until device is reset by toggling nSLEEP ON and OFF. What you can do here is to enable the current regulation which will regulate the inrush current to 6.5A.