Inquiring minds would like to see the driver circuit, if it be
possible (or not).
I'd guess it has active pullup of the output stage as well as the
previous active pull down.

I don't think you will get an immensely more useful justification for
drive resistors than you have already. I may be wrong.

Extremely rapid switching of the FET will increase dissipation
(article of faith :-) ).

Gate ringing is said to be promoted by direct drive (AOF).

RFI will increase with very fast high amplitude edges.

Next to fig 10 from the very useful IR "Application Note AN-937 Gate
Drive Characteristics and Requirements for HEXFET Power MOSFETs

              http://www.irf.com/technical-info/appnotes/an-937.pdf

says
________
In many applications, when the HEXFET is turned on,
current transfers from a freewheeling diode into the
HEXFET . If the switching speed is high and the stray
inductances in the diode path are small, this transfer can
occur in such a short time as to cause a reverse recovery
current in the diode high enough to short out the dc bus. For
this reason, it may be necessary to slow down the turn-on of
the HEXFET while leaving the turn-off as fast as practical.
Low impedance pulse shaping circuits can be used for this
purpose, like the ones in Figures 12 and 13
______________

Not much direct help but related and superb
TI "Practical consdierations in high performance MOSFET, IGBT, and MCT
gate drive circuits."

           http://www.ti.com/lit/ml/slup097/slup097.pdf

Note boot-snap cct here to slow down FET tirn off

          http://www.onsemi.com/pub_link/Collateral/ADP3110-D.PDF


 Russell


On 12 August 2011 23:00, Forrest Christian <forrestc@imach.com> wrote:
> Ok, I finally got a circuit I'm happy with to level shift the
> mosfets.... =A0Basically I'm finally able to slew the gate voltage on a P
> channel mosfet between about Vcc and Vcc-15 in about 250ns from a
> bipolar totem pole output stage. =A0Vcc is around 32V in this application=
..
>
> Now comes the hard part - possibly slowing this back down with a gate
> resistor.
>
> I'm trying to figure out how to determine what, if any gate resistor is
> needed.
>
> The mosfet I'm using is a FQI22P10. =A0 I understand that from a
> reliability standpoint a gate resistor can both help with overcurrents
> in the driver, and also resolve di/dt and dv/dt issues in the mosfet.
> And possibly something else I've missed.
>
> On the driver side, the driver transistors consist of a totem pole pair
> of MMBTA06/MMBTA56 which are rated at 500mA continuous with no peak
> rating in the datasheet. =A0 Gate charge of 50nC discharged in 250nS seem=
s
> to indicate that we're around 200mA... is this the right way to do this
> math?
>
> The other issue is the di/dt and dv/dt ratings for the mosfet... =A0I
> really don't even know how to approach this.
>
> Is there a good guide to this somewhere? =A0Or some rules of thumb? =A0I'=
m
> tempted just to throw a 10 ohm resistor in there since I can live with
> the little bit of switching time which is added, but of course really
> would like to have an engineered answer to this.
>
> Thanks.
>
> -forrest
>
>
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