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DRV8841: Decay mode

Part Number: DRV8841


I have a few questions about the DRV8841 and hoping you can help or point me in the right direction. I've implemented the DRV8841 in my design but with current regulation disabled, meaning the current sense inputs and current scaling control pins have been grounded. The chip features a decay pin that selects a decay mode, either fast or slow, to be used when changing direction or braking. 

Even though I've disabled current regulation, does the chip still perform some form of decay mode? If left open, the datasheet indicates that it performs mixed decay.

I don't think this is the case but just wanted to clarify and if not, do you know what the control scheme is during braking? I'm not able to see the gate pins of the FETs so it's not clear what's happening internally.

  • Hi Gregory,

    Due to the inductive nature of the motor, the current through the motor will continue in the same direction if the H-Bridge is disabled or when a motor changes directions. In order to protect the FETs, body diodes are used to decay the current to avoid shoot through during these periods. 

    The decay mode is a current recirculation technique on how quickly the current decays to zero. In the pictures below you can see the fast and slow decay mode paths. 

    The current will need to decay with some current recirculation mode.

    During braking the slow decay mode is used. 

    Please see the the following app note for more information on current recirculation and decay modes: 

     https://www.ti.com/lit/an/slva321a/slva321a.pdf

    Best,

    David