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Hurry: DRV8412 (EVM) protection (current backflow, etc..)

fang circle
Prodigy 210 points
Other Parts Discussed in Thread: DRV8412, DRV8412DDWEVM

Hi there,

I'm going to use C2000 DSP (28335 ) PWM to drive DRV8412EVM directly. Both high voltage is around 3.3v, so no voltage level translation is needed, which would simplify hardware design, and is also good for performace.

But I am worring about high frequency PWM (may between 10KHz-100KHz, probably around 20-40KHz) may result in backflow current which further destroy the DSP (since signal wire is directly connected without any isolators). I can't find any suitable isolators for this purpose.

Can anybody tell me any risk if I do so? Detailed comments and advice are highly appreciated.

  • TI__Mastermind 21805 points

    Fang,

    On our EVMs, we generally do not include isolators between the DRV and MCU/DSP because backflow current is only a problem if the DRV device is operating outside of specifications. That is, the C2000 will be in danger if there are problems with the power supply or the DRV Vcc limits are exceeded. However, if the system needs to be high-reliability, then isolators may be necessary.

    What level of reliability are you looking for in your application? I may be able to point you towards some isolators if you need them.

    Thanks,

    Matt

  • in reply to Matt Hein
    Prodigy 210 points

    Matt,

    Sorry I don't get you very well.

    I checked DRV8412-C2-KIT_v131 schematic, it seems there is nothing but wire between DSP and DRV8412 for the pwm control signal, no isolators, no resistors, etc,. I am not sure whether F28335 controlcard is compatible with DRV8412-C2-KIT, however, on F28335 controlcard there is a resistor in almost each PWM channel.

    Also, there is no much information about MOSFET in the DRV8412 datasheet, and I don't know how to evaluate peak current & backflow current on the gate electrode for safeguard considerations.

    Do you mean it is safe if DRV8412 is operated within the specifications? And further for DRV8412DDWEVM, is it safe both to DRV device and C2000 if the input voltage (GVDD, PVDD, PWM, RESET, etc.) not beyond their recommended ranges specified in DRV8412(DRV8412EVM) datasheet? 

    One more question, I don't know how reliability level is divided, MTBF/MTRF, 5 9s/6 9s, system level/component level, or ... Anyway, about PWM control and power supply (GVDD, PVDD) on DRV device, can you recomend me for some high level isolators and for some medium level isolators?

    Thank you so much. Have a nice day:)

    Fang


  • in reply to fang circle
    Prodigy 90 points

    The inputs of DRV8412 are not connected directly to the gates of the output FET's. There are buffers/drivers in between. Probably several of them, check page 6 of the data sheet. So the inputs cannot "see" the load.

    Isolators may actually hurt the MTBF of your design. They are after all additional components that can fail.

     

  • in reply to Einar Sjaavik
    Prodigy 210 points

    It makes sense.

    Thanks