Strange MOSFET driver behaviour - Microchip TC4426
in [Design]
|
Prev: Please, DO NOT forget the only thing that matters on this planet........................……..
Next: Adios, amigos...
From: Didi on 10 May 2010 15:49 On May 10, 9:41 pm, Joerg <inva...(a)invalid.invalid> wrote: > ..... > ... 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 :-) Hmm, indeed they may have thought they can't be bitten from the other end of the galaxy... :-) > 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? Oh no, nothing. There is a 1uF 1206 decoupling cap at the bottom side of the SO-8, via-d straight into the power/GND pins. And the driver drives just the gate capacitance, drain disconnected. The same drivers work within < 100nS driving gates of FDS6985 which have something like 500pF gate capacitance, so it is not just R/C. As if they have some active current limiting inside. I won't spend time investigating, after all the 33151 work and have been first team regulars for me for decades. I posted this hoping that someone had the answer readily available :-). > And ask Jerry the cat whether he has a good alibi for the times the > circuit was left unattended ... Poor Jerry died aged 14 a few years back, he was the smartest cat I ever knew. He tried to fix a door we had blocked with a rod against his slamming (got around it, located the problem and tried to remove it, can you believe this) when he was < 1 year old... so he might have not been innocent on that either, I would not underestimate him :-). I wish he were still around.... still miss him. ------------------------------------------------------ Dimiter Popoff Transgalactic Instruments http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276/ Original message: http://groups.google.com/group/sci.electronics.design/msg/f2fbf869d8d350e3?dmode=source
From: Didi on 10 May 2010 16:01 On May 10, 10:34 pm, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Mon, 10 May 2010 09:53:57 -0700 (PDT)) it happened Didi > <d...(a)tgi-sci.com> wrote in > <33785897-ee61-4e81-ae30-cf767ff3b...(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. Well, their I2C EEPROMs work OK so I thought I'd give them a chance. But there you go, I should have known better :-). Have yet to identify the mystery of their MCUs popularity, don't these have to work, ROFL. Dimiter
From: John Larkin on 10 May 2010 16:06 On Mon, 10 May 2010 09:53:57 -0700 (PDT), Didi <dp(a)tgi-sci.com> 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). We've used MAX4420s to drive NTP15N40s through gate drive transformers and they were so fast we had to add gate resistors to slow things down. We switched 400 volts in something like 10 ns, as I recall. John
From: Didi on 10 May 2010 16:32 On May 10, 11:06 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Mon, 10 May 2010 09:53:57 -0700 (PDT), Didi <d...(a)tgi-sci.com> 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). > > We've used MAX4420s to drive NTP15N40s through gate drive transformers > and they were so fast we had to add gate resistors to slow things > down. We switched 400 volts in something like 10 ns, as I recall. > > John Have never tried them, just had a look - look really fast, being single driver per SO-8 is apparently for a reason :-). But my losses are mostly in the inductors - which I will have to address if I am to offer this for battery operation. One flyback transformer is on an iron powder core and is absolutely marginal at max power (where it won't get, OK), efficiency is 60 to 70% at most. I know you have been through that, is there a lot to gain by using kool mu or MPP? Something like 10W max., I am doing it at about 500 kHz. Dimiter
From: Joerg on 10 May 2010 17:06
Didi wrote: > On May 10, 9:41 pm, Joerg <inva...(a)invalid.invalid> wrote: >> ..... [...] >> And ask Jerry the cat whether he has a good alibi for the times the >> circuit was left unattended ... > > Poor Jerry died aged 14 a few years back, he was the smartest cat > I ever knew. He tried to fix a door we had blocked with a rod against > his slamming (got around it, located the problem and tried to remove > it, can you believe this) when he was < 1 year old... so he might > have not been innocent on that either, I would not > underestimate him :-). I wish he were still around.... still miss > him. > Our Rottweiler is 13 and you can see the he's failing. I dread that day but we have to be there for them until the end. Contrary to scientific beliefs animals can do rational thinking and planning. Our Sheperd has done stuff when she was younger, for example stealing a freshly baked roll from underneath an aluminum foil wraper, _then_ putting the wrapper back on. The crumbs in her basket evidenced the mischief though, she didn't have enough time to clean that up. You could literally see that "Darn!" expression on her face. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |