Chris:
Thanks for the information.
Am I correct assuming that the voltage build up on the source reflecting
back to the gate is via the gate-source capacitance? If so, where would I be
using the ammobeads? Would a fast Schottky diode across the drain and source
be a better option?
Alan Pearce had a suggestion about the Intersil HIP4086 bridge driver. Is
this inherently superior to the IRF21362 part? Or am I better off getting a
FET with a higher gate threshold voltage and skirt the gate voltage spike
issue?
Thanks again for the help
Madhu



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Chris Eddy
Sent: Monday, September 17, 2001 3:43 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: IR21362 & IRF540N


You might find that if there is some inductance in the source of the low
side transistors, that there will be a voltage buildup on the source.
This is reflected back into the gate of the fet. There is a product by
Toshiba called Ammobeads. They will carve off the fast edges of the
false pulses to allow you to remove these spikes.  It depends on
topology and application, but they have helped me in the past. I suggest
going to Toshiba's site and doing a word search.

Chris~

Madhu Annapragada wrote:
>
> ..are as close to the 21362 pins as possible. I see very little noise on
my
> PWM output waveforms except for this nasty 50ns long 7V spike just before
> the top FEt turns off. I can get my motors spinning and my load moving
fine.
> I am just worried about the long term reliability with the FETs running
hot
> and EMI from shoot through currents. Any ideas? I appreciate your time and
I
> can send you the scope trace if you have the time to look at it.

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