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DRV8353R: Increasing gate drive current

Chris Doughty
Intellectual 295 points
Part Number: DRV8353R
Other Parts Discussed in Thread: DRV8353

Hi.  I am using the DRV8353RH in a high-current motor-control application which requires multiple, paralleled FETs to keep the Rds power dissipation down.  Adding the FETs has increased the total gate charge and the math is telling me I need to increase my gate drive beyond what the IC is normally capable of.  On the low-side, I think I'm in good shape.  Insert a FET driver on the low-side gate lines, power the driver off of VGLS, ensuring the current doesn't exceed the 25mA available, and (conceptually) I'm good to go.  The high-side (HS) has me a bit confused, however.  Normally, I would expect the HS drive voltage to be referenced to the source of the upper-half N-FET.  In this way, we'd always have ~12V to put across Vgs for turn-on.  On the DRV8353 however, the charge pump/HS voltage is referenced to the HS FET drains.  I suppose this allows the use of only a single charge pump across 3 half-bridges, but I'm at a bit of a loss as how to wedge additional gate drive in here.  Any thoughts?

  • 0
    TI__Guru 65220 points
    Chris,

    I'm not sure why you need an intermediary gate driver between the DRV and FETS. Can you share your schematic?

    Our DRV should be able to drive many FETs in parallel and it has a huge amount of gate drive current.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Intellectual 295 points

    Thanks for getting back to me, Adam!  Well, the plan is to run a DC motor at a maximum of 300A.  I have 4 each of these Toshiba TPH2R608NH FETs paralleled in each leg and each one has a max input capacitance of 6nF.  I'm looking pretty good for conduction but the power dissipation from switching is pretty bad unless I really turn the FETs on quickly.  My calcs suggest about 9A to get to the minimum turn-on/off times that the part will support.  I'd be happy to be corrected and be able to run directly off the DRV8353, however!

  • 0 in reply to Chris Doughty
    TI__Guru 65220 points
    Chris,

    For Idrive calculation we mostly look at the Qgd. Since you have parallel FETs and gate resistors, max Idrive is recommended and gate resistors may need to be reduced if drive strength is not enough currently.

    What calculation leads you to 9A?

    The gate resistors you're using would help with balancing between the several paralleled gates but they could easily be reduced to speed up the gate turn on.

    We have many customers driving several parallel FETS with current of 300A or higher driven directly by the DRV without intermediate secondary gate drivers.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Intellectual 295 points
    I was calculating the rise time to push the full gate capacitance up to the full on-voltage. Probably overly conservative, eh? It looks a lot better, even with my balancing resistors. Thanks!
  • 0 in reply to Chris Doughty
    TI__Guru 65220 points
    Chris,

    Yes I would say this is over conservative. Rise time is majorly dominated by Qgd, not Qg. Qg is for full enhancement but once you overcome Qgd, you're most of the way there.

    Regards,

    -Adam