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DRV8870: overcurrent value when fast current decay

Amber Si
Intellectual 2145 points
Part Number: DRV8870

Hi team,

When I use DRV8870 in coast mode(fast decay freewheel), there is peak current>6A, even 8A, duration time is < 2uS as below, but not trigger OCP. so I want to what is the current limit of the body diode in this mode?

Regards,

Amber

  • 0
    TI__Mastermind 19490 points

    Hi Amber,

    The freewheeling diodes are designed to handle large amounts of current during the dead time to avoid shoot through in coast mode. This dead time is typically 220 ns. 

    Please see the following app note for further understanding on Current Recirculation and Decay Modes.

    As long as the device is operated within the recommended operating parameters, the current limit of the body diode should be of no concern. 

    Was there a specific design limitation due to the diode current, or was this a general inquiry? 

    Best,

    David

  • 0 in reply to David Medis
    TI__Intellectual 2145 points

    Hi David,

    Thanks for your reply, so Does it mean  peak current of body diode>6A, even 8A in fast decay is tolerated? it will not have bad effect?

    Regards,

    Amber

  • 0 in reply to Amber Si
    TI__Mastermind 19490 points

    Hi Amber,

    Taking another look at the original scope image I was wondering what is the running motor current? The current can't change direction instantaneously and there is no reason the current in Coast Mode should be higher than the motor current. I would suggest recalibrating the current probe and seeing if the same measurements are made.

    If there is no specific reason to use Coast Mode I would suggest using brake mode to maintain motor torque. 

    The body diodes are rated the same as the FETs and therefore can handle the current the FET can handle. The FETs can handle a maximum of 6.4 A before OCP occurs and therefore the diodes will be rated the same. 

    Best,

    David