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DRV8305: RMS Drive Current

Christopher Liu
Prodigy 20 points
Part Number: DRV8305
Other Parts Discussed in Thread: DRV832X

Hi,

I was wondering what limits the RMS Drive current of the gate driver to 30mA? The datasheet mentions that the charge pump limits this, but is it a thermal issue on the charge pump or possibly a time constant related issue? Is there any way that I could increase this value with better cooling or drive the device at a higher voltage? The switches I'm using need ~80 nC and I'd like to switch at 128kHz which puts me at 60mA RMS using the formula on page 46 of the datasheet. Any help would be much appreciated.

Thanks,

Chris

  • 0
    TI__Expert 4650 points

    Hi Christopher,

    The equation shown on page 46 is assuming that all 6 MOSFETs could be switching, like in an application using Field Oriented Control to spin a BLDC.  This would be the worst-case stress on the Charge Pump.


    For something like simple 6-step trapezoidal control, the stress on the charge pump will be less and can be calculated using either 2 or 4 for the number of MOSFETs switching simultaneously.  This will give you an RMS current somewhere in the area of 20 - 40 mA instead of the 60 mA you previously calculated.  Also keep in mind that this is a first-order approximation of your RMS currents, so the actual value measured in your system will vary.

  • 0 in reply to Phil Beard
    Prodigy 20 points
    Hi Phil,

    I see, I was planning on starting with 6-step trapezoidal control, but I would like the option to move to FOC to spin the BLDC. I noticed on the DRV832X datasheet that the Ivcp is dependent on the supply voltage. If I were to increase the supply voltage and actively cool the device would I be able to perform past the rated current?

    Alternatively, is there any other device you could recommend that can handle a larger RMS drive current?

    Thank you very much,
    Chris