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DRV8328: compatible Mosfet device with gate driver DRV8328

Giorgio Valente
Prodigy 180 points
Part Number: DRV8328

Hello

I'm designing a BLDC drive unit following the design material of the TI dev board DRV8328AEVM. I've already bought the gate driver DRV8328 and ideally I would have bought the same Mosfet devices of the TI dev board (CSD18536KTTT) but it's out of stock and unfortunately I couldn't find an available device from TI. However, I think I've found a suitable device from onsemi. The ratings are similar to the CSD18536KTTT but some parameters are different. For the CSD18536KTTT, the gate-source threshold voltage, gate charge and gate-drain charge are 2.2V, 108nC and 14nC respectively while for the onsemi device the values are 4V, 45nC and 7nC. So basically the device I'm choosing has got higher gate-source threshold voltage (4V instead of 2.2V) but lower gate charge (45nC instead of 108nC). Do you think it can still be controlled with the gate driver DRV8328? What external gate resistance value should I choose? I know that the selection of external gate resistance is an iterative process but based on the Mosfet and gate driver devices chosen is it possible to select a good staring value?

thanks

Giorgio

  • +1
    TI__Mastermind 18916 points

    Hi Giorgio, 

    I think there might be a MOSFET gate-drive calculator tool somewhere on a product page, but will have to consult my team members for an answer on its location. 

    I think for an initial answer, below info should help:

    • App note: https://www.ti.com/lit/an/slva714d/slva714d.pdf
    • Typically we think of gate-drive currents in the matter of impact on MOSFET VDS slew rate
      • it's important not to turn on the MOSFETs channel too quickly, otherwise you get overshoot/undershoot voltage transients that cause ringing and damage to the MOSFETs. 
      • Therefore if we use the equation: t_Slew = Qgd / I_Source, we can aim for a reasonable Slew time (more than 100nanoseconds) 
      • and the I_Source can be evaluated based on the combination of gate drive voltage supply and fixed internal pull-up/pull-down resistances and external series gate resistances (Isource = V/R, where R is the total resistance) 
    • Experimental evaluation will still be useful, since there are many things like PCB layout parasitics that could impact the Slew rates 

    MOSFET slew rate and turn-on profile: 

    internal resistances and source/sink current limits: 

    Slew rate control: 

    Best Regards, 
    Andrew 

  • +1
    TI__Mastermind 18916 points

    Hi Giorgio, 

    Just wanting to follow up here and see if my earlier answer helped resolve your question - 

    • to re-iterate, the app note contents should give a lot of good guidance on selecting the components based on slew rate calculations 

    I followed up w/ a colleague and aligned that we don't currently have a calculator tool available for this, but will keep that in mind for future evaluations.

    Best Regards, 
    Andrew 

  • 0
    TI__Mastermind 18916 points

    Hi Giorgio, 

    Just following up here - please let us know if my earlier answer resolved your question & mark the thread as such if that's the case.

    Thanks! 

    Best Regards, 
    Andrew