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DRV8701: DRV8701

Larry Brick
Prodigy 250 points
Part Number: DRV8701

I am using a DRV8701 as a load reversing relay.  In all aspects the circuit seems to work fine.  I can reverse direction of a motor or a load at 2.5A-3.0A.  If I short the output and then enable the circuit, the fault LED comes on and it appears that the circuit is in hiccup mode as I would expect.  However if my load is enabled (and everything is running normally), then I short the load, I destroy one of my MOSFET's.  It seems that the protection circuit which triggers the Fault LED only functions at startup and not when the output is engaged then shorted.  My IDRIVE resistor value is 511K, my reference voltage is 3.3V and My Rsense resistor is 25mohm.  My MOSFETS are STL50DN6F7 (2 each, duals) configured so that only one half of each of the duals is on at any one time.  Your help is appreciated.  Thank you.

  • 0
    TI__Mastermind 37683 points

    Hi Larry,

    Thank you for posting to motor drivers forum.

    • What is the operating voltage VM?
    • How are you performing the short while the output is enable? If possible can you send a detailed procedure or diagram to help me understand?
    • Did you observe the damage to the MOSFET in more that one DRV8701 unit? Or did this damage only occur in one unit?
    • Did you capture any waveforms that you can share with me?
  • 0 in reply to Pablo Armet
    Prodigy 250 points

    VM voltage is 24VDC.  The load was a resistor and a jumper wire was clipped directly across the resistor to cause the short.  I am only testing the one prototype at this time.  The MOSFET failed shorted.  No waveforms were captured.

  • 0 in reply to Larry Brick
    TI__Mastermind 37683 points

    Hi Larry,

    Thank you for the information.

    After the initial experiment, did you replace either the MOSFET or the driver from the prototype board and retry the short test? I am just curious whether the damage can be replicated. If this is the case, then we can eliminate the possibility of an event like accidental ESD or short somewhere else on the circuit causing the failure.

    Based on the information It is hard to determine the root cause of the failure. The device should be able to protect itself by disabling the outputs when an OCP event occurs such as when the outputs are shorted. This OCP protection feature should work whether a load is driven or not. I suspect a large and fast enough transient spike occurred during the short that was too fast for the driver to trigger the OCP fault. For this device, the OCP deglitch time is 4.5µs. Then the device will retry after 3ms but will trigger OCP fault again if the fault persists.

    Did you notice the damage as soon as the short happened?

  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hi Larry,

    Do you have any updates for me? Were you able to figure out the cause of the problem?

  • 0 in reply to Pablo Armet
    Prodigy 250 points

    Hello Pablo.  I have not been able to determine the problem.  Because I am short on time, I am looking at an alternate design at this time.

  • 0 in reply to Larry Brick
    TI__Mastermind 37683 points

    Larry,

    I will close this thread for now then. Feel free to reply back to this thread or create a new post if you need further assistance.