zapping gates

[Stanislaw Flatto]

I thought the numbers were interesting, and thought others might have
data on other parts. I didn't expect to get ragged over methodology,
especially from a bunch of people who sound like armchair engineers.

I like your musical expertise.
OK. How about "armchair" in "Fouga Magister" (no parashute, "We don't
need it at 6 meters above water" - the test pilot declaration) with the
Honeywell UV recorder on my knees, to do some "armchair" testing at
600km/h.

John

Stanislaw
Slack user from Ulladulla.

 

[Fred Bartoli]

Not offensive, just very, very silly. I mean, I told everybody exactly
what I did, like turning the pot on the power supply and reading the
meter, and then people ask me stuff like what kind of supply I used,
and how many volts/ns were applied.

Hey, they forgot to ask what was the total RMS noise and its PSD, if it
changed with the applied voltage, what was the leads inductance, the
coupling factor between the D-S and G-S loops and also how many neutrinos
crossed the die during the experiment.

That's the way I'd define the experiment conditions, plus some others I sure
forget.
Not very serious testing engineers, aren't they?

 

[John Larkin]

Without going back and re-reading the beginning of the thread, it
sounded more like he had a small number of unexplained failures on an
existing product and trying to rule out or rule in gate overvoltage as
a possible cause.

Yup, that's about what's going on. The gadgets never fail here, in
test/burnin, but sometimes they fail in the field. We're performing
all sorts of abuse here, but no failures so far... low-rate failures
are hard to pin down.

During the investigation, we have found two bugs in the customer's
system that drives our box but, alas, I can't honestly blame the
failures on them.

I like to test parts to failure and remember the numbers, like my 0603
resistor that failed at 1600 volts.


John

 

[John Larkin]

Hmmm.... you appear to have a locked creativity problem.

Look for other avenues. (I have no suggestions.... other than a hairy single
seater flying thing)

Ah, the John Denver solution.

John

 

[dalai lamah]

Un bel giorno John Larkin digitò:

IR IRFPS37N50A n-channel 115 volts

Since this thread has gone a little polemic, please don't misunderstand me
when I ask you (with all the good intentions): what were you trying to
prove? If datasheet says Vgsmax is 30 V, I think it's safe to stay under
30V, no matter how conservative are the absolute ratings. What good will
make (in general and in your specific case) to know that a single model
withstood 115 V?

 

[John Larkin]

For those who are interested in this topic, it may be of value to read this
document:

http://www.irf.com/technical-info/appnotes/an-986.pdf

In particular section III. "Experimental verification" under the
observations 1. and 3. will be of interest. Basically they claim standard
gate MOSFETs typically are destroyed around 70-80V, with logic level devices
around 45V-50V. Additionally, if gate avalanche currents are limited to a
very small level (IE: <100uA) the gates don't seem to be immediately
destroyed. I've seen this basic data also claimed in at least one other
document from International Rectifier, but unfortunately I can't remember
exactly what document that was in.

John's IRFPS37N50A 115V figure is entirely believable and probably not at
all unusual for MOSFETs with datasheet absolute maximum gate ratings of
+/-30V. For absolute maximum rated +/-20V devices, I would expect 80V
breakdown to be more typical.

Manufacturers benefit in more than one way by producing datasheets with very
conservative maximum gate voltage ratings. In particular, devices will
still be more reliable at lower gate voltage (especially over the long run),
and it will help to improve product yield. For example, if during the
manufacturing process a tiny fleck of dust were to land on a MOSFET while
the gate oxide is being grown, it would no doubt introduce a gate oxide
imperfection that would reduce the gate breakdown voltage (though not
necessarily enough to make the device useless). For example, suppose the
imperfection reduces the breakdown voltage from 80V down to 40V. The device
can still be sold if the datasheet specifies 20V abs. max voltage, but it
could not be sold if the datasheet specified 60V absolute max.

Additionally, there is essentially no benefit (in terms of on resistance or
maximum current handling ability) for driving MOSFET gates beyond 20V, or
even 15V for that matter, for typical MOSFETs (there are some that still
benefit a little, but most don't). For the most part the on resistance and
maximum current capability with Vgs at 10V is essentially very nearly as
good as it will get regardless of how high a voltage you apply.

Interesting; thanks for the link. It's a pretty wordy paper, but the
conclusion...

VI. Conclusions
The use of a capacitive discharge into the gate to identify ESD
sensitivity of a MOS-gated transistor does not seem to
provide any additional information beyond what can be obtained more
accurately from a curve tracer and simple
calculations.
It is recommended that, for MOS-gated power transistors, the ESD test
circuits shown in Figure 2 be replaced by a
simple dielectric strength test performed with a curve tracer,
completed by simple calculations, as per Figure 3.


implies that rate effects aren't important.

There's no date on the paper, but they do refer to a "memoscope."

John

 

[Jim Thompson]

On Mon, 15 May 2006 10:51:38 -0700, John Larkin

[snip]

VI. Conclusions
The use of a capacitive discharge into the gate to identify ESD
sensitivity of a MOS-gated transistor does not seem to
provide any additional information beyond what can be obtained more
accurately from a curve tracer and simple
calculations.
It is recommended that, for MOS-gated power transistors, the ESD test
circuits shown in Figure 2 be replaced by a
simple dielectric strength test performed with a curve tracer,
completed by simple calculations, as per Figure 3.


implies that rate effects aren't important.

There's no date on the paper, but they do refer to a "memoscope."

John

Except that the actual failure mechanism is most likely metal
migration through "pin holes" in the oxide. "Rate" will cause hot
spots and thus affect the failure mechanism.

...Jim Thompson

 

[Genome]

Ah, the John Denver solution.

John

That's a bit above my head.

Wasn't he the bloke who played guitar, sang irritating songs with shit
lyrics and wore glasses? Not Roy Orbisson..... the other one.

How did these people manage to define the intelligence of the American
Nation?

Anyway $900,000 can't be too far from a second hand single military type jet
thingy. Get one with two to give the wife a bit of pleasure and put the
shits up the employees....

Is John Denver dead? Should I assume he buried his plane with himself in it?
Can I assume that you will not make the same mistakes?

DNA

 

[John Larkin]

That's a bit above my head.

Wasn't he the bloke who played guitar, sang irritating songs with shit
lyrics and wore glasses? Not Roy Orbisson..... the other one.

Roy ain't that bad. JD did "Rocky Mountain High" and "Country Road"
and some really repulsive love songs. He was weirder than Roy, in his
own way.

How did these people manage to define the intelligence of the American
Nation?

I once was deeply in love with a wonderful, beautiful woman until I
discovered that she had the complete collection of Barry Manilow
records.

Is John Denver dead? Should I assume he buried his plane with himself in it?
Can I assume that you will not make the same mistakes?

He took an ultralight out over the ocean, in southern California, and
apparently forgot to do the pre-flight checks, especially as regards
gas. I think flying a small plane is about as exciting as driving a
truck, although I might like to try sailplane aerobatics some day. If
I go violently, I'd prefer to ski off a cliff.

There was a teevee show on last week, about an Airbus 330 that ran out
of gas over the Atlantic, lost all power, turned around, glided for 20
minutes, and managed to land on a military airstrip in the Azores.
Impressive. I thought these things glided about as well as cinder
blocks.


John

 

[Jim Thompson]

On Mon, 15 May 2006 14:12:07 -0700, John Larkin

[snip]

There was a teevee show on last week, about an Airbus 330 that ran out
of gas over the Atlantic, lost all power, turned around, glided for 20
minutes, and managed to land on a military airstrip in the Azores.
Impressive. I thought these things glided about as well as cinder
blocks.


John

IIRC late '50's, early '60's. Some air transport company plane, 707,
ran out of fuel and sat down on Ohio State Route 7 (parallels the Ohio
River). Did just fine until they came to an overpass ;-) Stripped
the wings right off. Fortunately no fuel.

...Jim Thompson

 

[Joerg]

Hello John,

There was a teevee show on last week, about an Airbus 330 that ran out
of gas over the Atlantic, lost all power, turned around, glided for 20
minutes, and managed to land on a military airstrip in the Azores.
Impressive. I thought these things glided about as well as cinder
blocks.

The big iron isn't as bad as their size makes them appear to be. Once I
was on a 767 flight and about an hour shy of the Belgian coast an engine
quit. This meant there was only one engine left which luckily kept
humming. The pilots were able to bring it into Frankfurt/Germany on a
long stretch (but all the airspace was cleared and there were dozens of
fire trucks waiting...). The plane was yawing pretty badly but we made
it. Must have been a white-knuckle event for the pilots since they
really had to nail that landing well.

Regards, Joerg

 

[Richard Henry]

Hello John,


The big iron isn't as bad as their size makes them appear to be. Once I
was on a 767 flight and about an hour shy of the Belgian coast an engine
quit. This meant there was only one engine left which luckily kept
humming. The pilots were able to bring it into Frankfurt/Germany on a
long stretch (but all the airspace was cleared and there were dozens of
fire trucks waiting...). The plane was yawing pretty badly but we made
it. Must have been a white-knuckle event for the pilots since they
really had to nail that landing well.

Two-engine commercial planes that cannot function properly on one engine
should be banned.

 

[Fred]

message


How noisy was the knob? How steady was the guy turning the knob?

Approximately this noisy and that steady.

 

[Joerg]

Hello Richard,

Two-engine commercial planes that cannot function properly on one engine
should be banned.

The 767 certainly could function. But I guess they didn't know why the
first engine quit and were worried that the other one might as well.
Fuel contamination or whatever.

Regards, Joerg

 

[Stanislaw Flatto]

There's no date on the paper, but they do refer to a "memoscope."

John

This instrument preceded MOS-FET's few years I used a Tektronix and HP
ones in early '60.

 

[Tim Williams]

Two-engine commercial planes that cannot function properly on one engine
should be banned.

AFAIK, they are rated to fly with just one engine. Two are there for
reliability, not having to trim the rudder like hell, and of course higher
performance.

Tim

 

[Keith]

Roy ain't that bad. JD did "Rocky Mountain High" and "Country Road"
and some really repulsive love songs. He was weirder than Roy, in his
own way.


I once was deeply in love with a wonderful, beautiful woman until I
discovered that she had the complete collection of Barry Manilow
records.



He took an ultralight out over the ocean, in southern California, and
apparently forgot to do the pre-flight checks, especially as regards
gas.

Yes, but not an ultralight, a "home-built" Rutan Long-EZ[*]. JD
was known to be a dangerous pilot.

[*] http://en.wikipedia.org/wiki/Long-EZ

I think flying a small plane is about as exciting as driving a
truck, although I might like to try sailplane aerobatics some day. If
I go violently, I'd prefer to ski off a cliff.

There was a teevee show on last week, about an Airbus 330 that ran out
of gas over the Atlantic, lost all power, turned around, glided for 20
minutes, and managed to land on a military airstrip in the Azores.
Impressive. I thought these things glided about as well as cinder
blocks.

Commercial jets can do a 10:1 glide ratio, at least. If they're
30k ft (6 miles) up... The amazing thing is that they had power to
get the thing down.

 

[John Larkin]

Commercial jets can do a 10:1 glide ratio, at least. If they're
30k ft (6 miles) up... The amazing thing is that they had power to
get the thing down.

Yeah. The rate of descent must have been roughly 1000 fpm, as they
arrived at the island at about 10,000 feet. They circled a bit and
came in at 250 mph...no flaps! Good thing it's a 2-mile military
runway, one of the Shuttle backup strips. The gear caught fire but of
course there was no fuel to burn.

One of my customers, the Hamilton-Sundstrand div of United
Technologies, makes aircraft power systems. They make "the thing you
never want to see used", a little propeller-powered generator. When
all else is dead, as on the A330, the pilot pulls a lever, a hatch
opens, and this thing drops into the airstream.

It does surprise me the the same fuel supply is apparently used for
the main engines and for the APU.

John

 

[Pooh Bear]

Yeah. The rate of descent must have been roughly 1000 fpm, as they
arrived at the island at about 10,000 feet. They circled a bit and
came in at 250 mph...no flaps! Good thing it's a 2-mile military
runway, one of the Shuttle backup strips. The gear caught fire but of
course there was no fuel to burn.

One of my customers, the Hamilton-Sundstrand div of United
Technologies, makes aircraft power systems. They make "the thing you
never want to see used", a little propeller-powered generator. When
all else is dead, as on the A330, the pilot pulls a lever, a hatch
opens, and this thing drops into the airstream.

Canadian airlines have a history of gliding airliners ( the A330 in this case
was operated by Air Transat ). In 1983 an Air Canada Boeing 767 ran out of fuel
enroute and also managed to glide succesfully to a suitable runway.
http://en.wikipedia.org/wiki/Gimli_Glider

The two aircraft are apparently known unofficially to aircrew as the Gimli
Glider and the Azores Glider.

It does surprise me the the same fuel supply is apparently used for
the main engines and for the APU.

You'd hate to have some APU fuel left should the main engines flame out.

Graham

 

[Robert Latest]

On Tue, 16 May 2006 08:28:10 -0700,

Technologies, makes aircraft power systems. They make "the thing you
never want to see used", a little propeller-powered generator. When
all else is dead, as on the A330, the pilot pulls a lever, a hatch
opens, and this thing drops into the airstream.

Is that a standard thing on commercial aircraft?

robert