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Original question:

DRV8871: Input Transient Voltage Protection

DRV8871: Transient Voltage Protection at Output Pins

Nicholas Reilly
Prodigy 60 points
Part Number: DRV8871

Hello,

I am using the DRV8871 in an aerospace application, where the motor drive output pins (out+ and out-) may be subjected to a lightning threat.  We are trying to select an appropriate TVS diode to use as protection on these lines.  

The question I have is: What transient voltage levels can these pins survive for a short duration (anywhere from 5us to 100us) without risking damage to the device?  We will be using a supply of VM = 28V.  

Thank you,

Nick

  • 0
    TI__Guru** 114905 points

    Hi Nick,

    Please note the absolute maximum ratings of the device.

    The pins can survive up to the absolute maximum current of 3.5A and voltage of VM + 0.7V and -0.7V .

    If the current through the body diodes is less than 3.5A and the voltage remains below the VM and node pin abs max, there should be no issue.

  • 0 in reply to Rick Duncan
    Prodigy 60 points

    Hi Rick,

    In order to limit the current through the body diodes during a transient lightning event, we plan to use external schottky diodes to steer the current around the DRV8871 and back into the supply, bypassing the internal body diodes. 

    We understand this will also steer any motor recirculation current through the external diodes instead of the body diodes due to the lower Vf of the schottky diodes.  Do you see any issues with this method?  We are wondering if it will have any impact on the internal protection features of the DRV8871, or if there will be any other impact to the operation of the driver as a result.

    Thank you,

    Nick

  • 0 in reply to Nicholas Reilly
    TI__Guru** 114905 points

    Hi Nick,

    As long as the absolute ratings are met during this event, there should be no impact. So steering the current through external diodes should not be an issue unless the VM voltage exceeds the abs max ratings.