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DRV8832: Energy back into VCC bus if the motor is stallen.

Minqiu Xie
Mastermind 21565 points
Part Number: DRV8832

Hi team:

I have a question about the situation when motor is stallen suddenly.

Is there any risk that the energy will back to VCC bus, and charge the capacitor?

And I'm confused about the current limit and OCP function. What will the IC operate once the current reach the limit value and OCP value? 

  • 0
    TI__Guru** 114905 points

    Hi Minqiu,

    Is there any risk that the energy will back to VCC bus, and charge the capacitor?

    There are several conditions that can cause energy to flow back into the VCC bus and charge the capacitor. This is not a risk assuming the VCC bus remains below the absolute maximum ratings of the devices attached to the bus.

    And I'm confused about the current limit and OCP function. What will the IC operate once the current reach the limit value and OCP value? 


    The current limit is used to limit the current during startup and identify a stall condition. The current limit is lower than the overcurrent limit, and is set by using a resistor connected from ISENSE to GND.

    The overcurrent protection protects the device in the case the current is much higher and flows through other paths. Two examples are if an output is accidentally shorted to GND, or if the ISENSE resistor is connected to GND.  In both of these cases current above the overcurrent limit can flow through the FETs.

  • 0 in reply to Rick Duncan
    TI__Mastermind 21565 points

    Hi Rick:

    Thanks for your kind answer. But I'm still confused.

     

    Rick Duncan said:
    There are several conditions that can cause energy to flow back into the VCC bus and charge the capacitor. This is not a risk assuming the VCC bus remains below the absolute maximum ratings of the devices attached to the bus.
    But it's posible to charge the Cout higher than absolute maximum rating, right? And the fore circuit may have lower limit, it's dangerous for the system. May you show some detail case and explain how it happen? 

    Rick Duncan said:
    The current limit is used to limit the current during startup and identify a stall condition. The current limit is lower than the overcurrent limit, and is set by using a resistor connected from ISENSE to GND.

    Once the current reach the current limit, how does the circuit act? Will it turn off the FETs immediately? Or just decrease the duty cycle? 

     

    Rick Duncan said:
    The overcurrent protection protects the device in the case the current is much higher and flows through other paths. Two examples are if an output is accidentally shorted to GND, or if the ISENSE resistor is connected to GND.  In both of these cases current above the overcurrent limit can flow through the FETs.

    Similar question. Will all FETs turn off or it should wait for some time to act? 3us or 275ms?

    If it's convenience, I would like to consult you with email.

  • 0 in reply to Minqiu Xie
    TI__Guru** 114905 points

    Hi Minqiu,

    Rick Duncan
    There are several conditions that can cause energy to flow back into the VCC bus and charge the capacitor. This is not a risk assuming the VCC bus remains below the absolute maximum ratings of the devices attached to the bus.

    But it's posible to charge the Cout higher than absolute maximum rating, right? And the fore circuit may have lower limit, it's dangerous for the system. May you show some detail case and explain how it happen? 

    >>> It is possible to charge the COUT if COUT is too small to accept the motor current. As the current decays in the motor, the current flows into the VCC capacitor. Please refer to section 9.1 of the datasheet.

    Rick Duncan
    The current limit is used to limit the current during startup and identify a stall condition. The current limit is lower than the overcurrent limit, and is set by using a resistor connected from ISENSE to GND.

    Once the current reach the current limit, how does the circuit act? Will it turn off the FETs immediately? Or just decrease the duty cycle? 

     

    >>>  When the current limit is reached (VIsense = ~200mV), the outputs enter a decay mode to limit the current. We will have to confirm with decay mode (Coast or Brake).
    The duty cycle is not decreased.
    Rick Duncan
    The overcurrent protection protects the device in the case the current is much higher and flows through other paths. Two examples are if an output is accidentally shorted to GND, or if the ISENSE resistor is connected to GND.  In both of these cases current above the overcurrent limit can flow through the FETs.

    Similar question. Will all FETs turn off or it should wait for some time to act? 3us or 275ms?

    >>> In an overcurrent condition, the FETS are disabled within 2us (typical).Once disabled due to an overcurrent event, the device remains disabled until VCC is cycled.

    If it's convenience, I would like to consult you with email.