At 08:59 AM 7/9/2003 -0500, you wrote:
>Driving a large mosfet directly from any micro is a bad idea.

I think that's an over-generalization. Driving a power logic-level
MOSFET from a micro output pin is okay, preferably with a series gate
resistor to limit the current, PROVIDED the switching frequency is low.
The slow rise and fall times waste a bit of power at each switching,
but also lower EMI. If you're switching a big solenoid or a relay, you
don't really need to switch in 30ns, a few microseconds is fine.

>The gate capacitance will take a while to charge, since the on resistance
>of the fets in the micro is significant (>10-100 ohms)
>
>Use a driver like the Micrel MIC4429.
>I'm using this between an AVR and a TO-220 mosfet to switch power at 500kHz.
>The output rise and fall times are impressive, and the FET is staying nice
>and cold.

At 500kHz you sure *NEED* a nice driver like that. Note that Microchip also
has such drivers in their lineup- they can supply AMPS of current to the
gate. Eg. the TC4429 (6A drive).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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