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From: Didi on 10 May 2010 12:53
Not so long ago I put them in a design (the other Microchip part which
has
made it into my designs is an I2C EEPROM).
Worked as expected while driving tiny MOSFETs (two in an SO-8).

But when it came to an IRF540 - plain old IRF540 - they failed
miserably.
I first looked at them driving the IRF "empty", i.e. the drain
hanging, source
practically grounded (well, via 0.1 Ohm or so). Never got past this
with this
driver.

The edges got really bad - 500 nS if not worse, way beyond spec. I
checked
what happened with a series 10 Ohm resistor, nothing worth noting. OK,
at
the driver output the initial perhaps 1/5th or 1/4th of the voltage
excursion
got better.

Before I began trying things out etc. I replaced the TC4426 with a
good old
MC33151. Worked same as it has worked last 20+ years for me, well
under
100 nS (was something about 50-60).

I did not pursue it further, there was no point stopping at it. Got it
working
with the 33151, which was designed in times when apparently someone
would have noticed if a design did not work :-).

But a few days later I am still curious what was that. Looked as if
some
foldback current limiting - wanted by the designer or not - took
effect, perhaps
I could have eliminated it with a larger current limiting resistor so
things would
get usable (much worse than with the 33151, obviously, it would have
taken
perhaps 50+ Ohm).

Any thoughts?

Dimiter

------------------------------------------------------
Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------
http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/

From: Joerg on 10 May 2010 13:44
Didi wrote:
> Not so long ago I put them in a design (the other Microchip part which
> has
> made it into my designs is an I2C EEPROM).
> Worked as expected while driving tiny MOSFETs (two in an SO-8).
>
> But when it came to an IRF540 - plain old IRF540 - they failed
> miserably.
> I first looked at them driving the IRF "empty", i.e. the drain
> hanging, source
> practically grounded (well, via 0.1 Ohm or so). Never got past this
> with this
> driver.
>
> The edges got really bad - 500 nS if not worse, way beyond spec. I
> checked
> what happened with a series 10 Ohm resistor, nothing worth noting. OK,
> at
> the driver output the initial perhaps 1/5th or 1/4th of the voltage
> excursion
> got better.
>
> Before I began trying things out etc. I replaced the TC4426 with a
> good old
> MC33151. Worked same as it has worked last 20+ years for me, well
> under
> 100 nS (was something about 50-60).
>
> I did not pursue it further, there was no point stopping at it. Got it
> working
> with the 33151, which was designed in times when apparently someone
> would have noticed if a design did not work :-).
>
> But a few days later I am still curious what was that. Looked as if
> some
> foldback current limiting - wanted by the designer or not - took
> effect, perhaps
> I could have eliminated it with a larger current limiting resistor so
> things would
> get usable (much worse than with the 33151, obviously, it would have
> taken
> perhaps 50+ Ohm).
>
> Any thoughts?
>

IIRC most variants of the IRF540 are around 1700pF on the gate and the
TC4426 is really more a 1nF driver. Still, it should have done it in
under 100nsec. Sure that you didn't get bad chips or counterfeit ones?

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Didi on 10 May 2010 14:09
On May 10, 8:44 pm, Joerg <inva...(a)invalid.invalid> wrote:
> Didi wrote:
> > Not so long ago I put them in a design (the other Microchip part which
> > has
> > made it into my designs is an I2C EEPROM).
> > Worked as expected while driving tiny MOSFETs (two in an SO-8).
>
> > But when it came to an IRF540 - plain old IRF540 - they failed
> > miserably.
> > I first looked at them driving the IRF "empty", i.e. the drain
> > hanging, source
> > practically grounded (well, via 0.1 Ohm or so). Never got past this
> > with this
> > driver.
>
> > The edges got really bad - 500 nS if not worse, way beyond spec. I
> > checked
> > what happened with a series 10 Ohm resistor, nothing worth noting. OK,
> > at
> > the driver output the initial perhaps 1/5th or 1/4th of the voltage
> > excursion
> > got better.
>
> > Before I began trying things out etc. I replaced the TC4426 with a
> > good old
> > MC33151. Worked same as it has worked last 20+ years for me, well
> > under
> > 100 nS (was something about 50-60).
>
> > I did not pursue it further, there was no point stopping at it. Got it
> > working
> > with the 33151, which was designed in times when apparently someone
> > would have noticed if a design did not work :-).
>
> > But a few days later I am still curious what was that. Looked as if
> > some
> > foldback current limiting - wanted by the designer or not - took
> > effect, perhaps
> > I could have eliminated it with a larger current limiting resistor so
> > things would
> > get usable (much worse than with the 33151, obviously, it would have
> > taken
> > perhaps 50+ Ohm).
>
> > Any thoughts?
>
> IIRC most variants of the IRF540 are around 1700pF on the gate and the
> TC4426 is really more a 1nF driver. Still, it should have done it in
> under 100nsec. Sure that you didn't get bad chips or counterfeit ones?
>
> ....

Well, can't be sure of course. Got just 25 from Digikey for
the prototype.

Dimiter

------------------------------------------------------
Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------
http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/

From: Joerg on 10 May 2010 14:41
Didi wrote:
> On May 10, 8:44 pm, Joerg <inva...(a)invalid.invalid> wrote:
>> Didi wrote:
>>> Not so long ago I put them in a design (the other Microchip part which
>>> has
>>> made it into my designs is an I2C EEPROM).
>>> Worked as expected while driving tiny MOSFETs (two in an SO-8).
>>> But when it came to an IRF540 - plain old IRF540 - they failed
>>> miserably.
>>> I first looked at them driving the IRF "empty", i.e. the drain
>>> hanging, source
>>> practically grounded (well, via 0.1 Ohm or so). Never got past this
>>> with this
>>> driver.
>>> The edges got really bad - 500 nS if not worse, way beyond spec. I
>>> checked
>>> what happened with a series 10 Ohm resistor, nothing worth noting. OK,
>>> at
>>> the driver output the initial perhaps 1/5th or 1/4th of the voltage
>>> excursion
>>> got better.
>>> Before I began trying things out etc. I replaced the TC4426 with a
>>> good old
>>> MC33151. Worked same as it has worked last 20+ years for me, well
>>> under
>>> 100 nS (was something about 50-60).
>>> I did not pursue it further, there was no point stopping at it. Got it
>>> working
>>> with the 33151, which was designed in times when apparently someone
>>> would have noticed if a design did not work :-).
>>> But a few days later I am still curious what was that. Looked as if
>>> some
>>> foldback current limiting - wanted by the designer or not - took
>>> effect, perhaps
>>> I could have eliminated it with a larger current limiting resistor so
>>> things would
>>> get usable (much worse than with the 33151, obviously, it would have
>>> taken
>>> perhaps 50+ Ohm).
>>> Any thoughts?
>> IIRC most variants of the IRF540 are around 1700pF on the gate and the
>> TC4426 is really more a 1nF driver. Still, it should have done it in
>> under 100nsec. Sure that you didn't get bad chips or counterfeit ones?
>>
>> ....
>
> Well, can't be sure of course. Got just 25 from Digikey for
> the prototype.
>

Maybe they saw the word "Transgalactic" in the order and thought, oh,
better not send the real stuff :-)

But Digikey is usually a reliable source. Yet they could end up with a
bad lot from the mfg. I'd test these things for Rdson, something ain't
right there. No chance that some fat inductive spike or ESD gets in?

And ask Jerry the cat whether he has a good alibi for the times the
circuit was left unattended ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Jan Panteltje on 10 May 2010 15:34
On a sunny day (Mon, 10 May 2010 09:53:57 -0700 (PDT)) it happened Didi
<dp(a)tgi-sci.com> wrote in
<33785897-ee61-4e81-ae30-cf767ff3b81b(a)g21g2000yqk.googlegroups.com>:

>Not so long ago I put them in a design (the other Microchip part which
>has
>made it into my designs is an I2C EEPROM).
>Worked as expected while driving tiny MOSFETs (two in an SO-8).
>
>But when it came to an IRF540 - plain old IRF540 - they failed
>miserably.
>I first looked at them driving the IRF "empty", i.e. the drain
>hanging, source
>practically grounded (well, via 0.1 Ohm or so). Never got past this
>with this
>driver.
>
>The edges got really bad - 500 nS if not worse, way beyond spec. I
>checked
>what happened with a series 10 Ohm resistor, nothing worth noting. OK,
>at
>the driver output the initial perhaps 1/5th or 1/4th of the voltage
>excursion
>got better.
>
>Before I began trying things out etc. I replaced the TC4426 with a
>good old
>MC33151. Worked same as it has worked last 20+ years for me, well
>under
>100 nS (was something about 50-60).
>
>I did not pursue it further, there was no point stopping at it. Got it
>working
>with the 33151, which was designed in times when apparently someone
>would have noticed if a design did not work :-).
>
>But a few days later I am still curious what was that. Looked as if
>some
>foldback current limiting - wanted by the designer or not - took
>effect, perhaps
>I could have eliminated it with a larger current limiting resistor so
>things would
>get usable (much worse than with the 33151, obviously, it would have
>taken
>perhaps 50+ Ohm).
>
>Any thoughts?

Yep, stay clear of Microfip.
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