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DRV8701: DRV8701 Freewheel Diodes required?

John Easton
Prodigy 200 points
Part Number: DRV8701
Other Parts Discussed in Thread: TIDA-00620, DRV8871, DRV8870, DRV8872

Hello,

I am working on a Brushed motor driver based on a DRV8701with CSD18540Q5BT mosfets to Drive a 24V 50W BDC Gearmotor. For reference I have purchased a DRV8701-EVM eval board, and I am referring to TIDA-00620, DRV8701 & DRV8701-EVM datasheet.

This is my first attempt at designing a motor driver from scratch, I have always used L6203 designs in the past.  I am pretty happy with the overall design, but I have a couple of questions regarding protecting the mosfets during sudden braking/direction change etc. Using the L6203, I would place a RC snubber across the motor output, and a TVS, which limited spikes across the VM rail to a minimal value.

I have noticed that there are no external freewheeling diodes across the mosfets in any of the designs. Is this because the internal mosfet diode is considered to be sufficient?  Should I allow space on my pcb for external diodes? Also, is there any other protection I should allow for on the Mosfet bridge output to protect against sudden motor stop or direction change?

Kind Regards

John

  • 0
    TI__Guru** 114905 points
    Hi John,

    The internal mosfet diode typically can handle the current when freewheeling.

    For concerns about voltage spikes, adding space for additional circuitry is usually a good idea if the space is available.

    FYI -- At 50W, the DRV8870, DRV8871, or DRV8872 may also work.
  • 0 in reply to Rick Duncan
    Prodigy 200 points

    Thank you for your reply Rick, much appreciated.

    Do you have any recommendations for smoothing/clamping spikes on the H-Bridge output? Is a RC Snubber and or Transzorb a suitable solution? I looked through the TI database, but didn't really find a solution.

    Kind Regards

    John

  • 0 in reply to John Easton
    TI__Guru** 114905 points

    Hi John,

    A RC snubber and/or Transzorb are suitable.

    Providing a solution to voltage spikes is difficult because the applications vary significantly.

    It is important to evaluate the maximum voltages of the system under extreme conditions to confirm the absolute maximum voltages are not violated.