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DRV8870: Inquiry about operation when ISEN pin is connected to GND

JH Shin
Mastermind 7145 points
Part Number: DRV8870

Hello,

My customer has some questions regarding the operation when the ISEN pin is connected to GND.

They understand that the current limiting feature of the DRV8870 feature is not used if the ISEN pin is connected to GND.

Q1) When ISEN is connected to GND, does it only trip 3.6A for a few hundred milliseconds?

Q2) When ISEN is connected to GND, is the Itrip value set to 3.6A?

    Q2-1) If it is correct that the Itrip value is set to 3.6A, does this mean that the motor driver will not be damaged even if the motor continuously uses 3.6A?

Q3) If there is no current limitation when ISEN is connected to GND, will the motor driver be damaged if the motor draws a current of more than 3.6A?

Q4) What is the difference between Overcurrent protection trip level (3.7V~6.4V) and Itrip?

Thank you.

JH

  • 0
    TI__Expert 5980 points

    Hi JH,

    When ITRIP is reached, the slow decay mode is enabled for the tOFF time.

    If the current exceeds the overcurrent protection threshold for the overcurrent deglitch time (tOCP) all FETS will be disabled for over the tRETRY time.

    Yes, if the ISEN pin is connected to ground, the peak current will reach 3.6 A for a few hundred milliseconds before OCP or TSD is reached.

    Best,

    David

  • 0 in reply to David Medis
    Mastermind 7145 points

    Hi David,

    Thanks for your reply.

    The customer wants more clarification on your answer below.

    7.4.1 PWM With Current Regulation

    In the case above, even if a high current is continuously drawn from the motor, the trip is repeated at 2.2A, so the motor current can be controlled at 2.2A.

    7.4.2 PWM Without Current Regulation

    In the case above, it is understood that even if the motor continuously draws high current, 3.6A is supplied for hundreds of mS, and then repeated after about 3ms (tRETRY) after the H-bridge is disabled and turned off by OCP or TSD.

    Is there no effect on the IC even if OCP and TSD are continuously repeated when a high current is continuously drawn using 'PWM Without Current Regulation'?

    Thanks,

    JH

  • +1 in reply to JH Shin
    TI__Expert 5980 points

    Hi JH,

    Yes, in the first case (PWM with current regulation) the motor current will be regulated and trip at 2.2 A.

    The second case (PWM without current regulation) the motor current will not be regulated and trip at 3.6 A.  For any current that exceeds 3.6 A (in any case) for a few hundred mS will trigger OCP or TSD. This will protect the device for short periods of time from any spikes in current from inrush or the motor supply. 

    It is not recommended to "continuously" trigger OCP or TSD for extended periods of time. Operating outside of the recommended range could affect device reliability. 

    Best,

    David