Teensy 4.0 Brushed Motor and Mosfet get hot

Personally I have used an ONsemi FDD3706 FET several times. No driver, just connected the Teensy pin directly to the gate.
If my calculations were right, the gate current was only 7mA with a rise and fall time of 500ns.
The FET never got hot [but I never operated it at 20kHz PWM frequency].

Paul
 
Did you read that from figure 2-22? I wouldn't draw that conclusion...

I'd definitely agree with that - a "typical" graph in a device with FET output drivers isn't worth much. The manufacturing spread
for thresholds in FETs is large (sometimes several volts), go by worst-case parameters only. the MIC4416 is quoted for 4.5V,
so that's guaranteed, but 3.7V all bets are off, whatever a typical graph may say, because they won't be testing that on the
quality control step in the production line.

There are many many FET drivers out there, and some will be fine with 3V supply, that's the sort of driver to pick.
 
I feared that, that's why I ordered an oscilloscope... for less then 50€ haha.
I hope I can see anything with it. I will then post a picture. Thank you Paul! I think now this goes into the right direction
 
If you can wait for a few days, I will do a test with an 8520 dronemotor on a Teensy 4.0 using the FFD3706 FET here as well.

Paul
 
MarkT I feel the same way! But I actually couldn't find a driver ... I was very desperate.

If the Mic4416 really does not provide enough output, then I build a push-pull circuit myself. Unless, of course, you know a good driver.

Then I ask myself why the mosfet got just as hot when I reduced the frequency to 1khz. I logically did that at first. Then I ended up here confused
 
Again in my defense: I didn't just bet on the MIC4416 because the figure in the data sheet looks as if it would deliver a sufficient output even below 4.5V. I also looked around for other drivers from the manufacturer that are officially designed for 3V. Then I compared the figures with those of the MIC4416. It turned out that some of the graphs were identical, which led me to the conclusion, that they might be using the same mosfets internally. And that's exactly what I bet on. And let's be honest, it would be rather unrealistic if at 4.5V you have 250mA output and at 4V you have suddenly nothing. Therefore, I have estimated that with a little luck (yes, I admit that) at 3.6V, even 50mA could be at the output, which is enough for my Mosfet to turn off and on hard.

In addition, for me a data sheet is strictly speaking nothing more than marketing. It's about selling a product. And sometimes the customer shouldn't even know that the basic model can secretly do the same thing as an expensive model.

Let's see what the measurements show in the next few days.
 
A driver that handles 4.5V to 18V has to use thicker gate oxide in its output devices than one rated for 3V upto 8V, for instance.
Thicker gate oxide means higher thresholds and plateaus, and more variation in both, but also will survive higher Vgs transients.

Datasheets are the basis of any legal dispute about an electronic component, so there are de-facto legal documents (I'm sure most/all
companies have disclaimers about accuracy of datasheets, but they can't just put provably incorrect claims in them and expect
no recourse if they don't fix errors / inaccuracies - that would be fraudulent as I understand it. But only guaranteed values / worst-case
parameters are actually a claim about the device, everything else could be viewed as marketing I suppose, but certainly most graphs
are "typical", which has no actual utility other than interest value - you certainly can't infer two products are the same if the graphs are the
same, they might just have been copy/pasted. You do sometimes see ensemble graphs from a sampling of product to give an
idea of spread, which is definitely much more useful, and sometimes you get min/max bounds graphs, again useful.

And the corollory holds - if you have components fail, but the manufacturer can establish you exceeded the absolute maximum
ratings, you are unlikely to have much luck getting money back.

So a lot of a datasheet has legal ramifications, which is why they usually are pretty reliable (so long as you read all the notes and
caveats, and purchase the actual product, not a counterfeit...)

These days of course you have to use what's actually in stock, I suspect this is going to have knock-on effects in future years when
we discover many products compromised on parts during the chip shortage...
 
Sorry, I think the phrase "nothing but marketing" was very exaggerated by me. But I hope you understand what I was trying to say.
 
I have a funny question. What would happen if I just connect two pins from the Teensy together Then they should be able to deliver more current for the gate? If I then lower the pwm frequency to let's say 10khz, then I slowly come into the range, where I could connect the Teensy directly to the MOSFET without a driver.
Would the PWM signal be synchronous at all? I have no idea...

I would also be interested in how quickly and whether the Teensy really breaks if I reduce the gate resistance even further. I know the Tennsy 4.0 has a maximum of 4mA constant per pin. But when controlling the Mosfet, the current only goes up until the gate is charged.
That is definitely not good solution, no question about it, but there are so many people who run their mosfets without gate resistance at all...

I'm looking forward to your opinions on this.
Either way, I'll try out how the Teensy behaves without gate resistance. One learns from mistakes. At least I do 😉
 
Interesting...the biggest setback is probably the analog bandwith of only 200kHz, which makes this scope of limited use [to say it nicely].

Paul
 
Yes, that was said very nicely ;) I already had some portable oscilloscopes. So far I've sent them all back because I couldn't even properly display a simple pwm signal. The biggest problem I had was mostly that the picture never really stood still. The curves wander back and forth. With the most expensive devices, I think you can wander back and forth in memory and focus on a certain area. We will see...
 
I have that one (6022BE) . Not worth the money, the PC Software is not usable. unusabel. Its just !"§$%&.
If anyone is interested in it, I can search if it is in any box....
@PaulS, if you want to test it, I can send it to you... (If I find it)

The Hantek DSO510x are pretty OK.
 
Funny I had the same thought. I looked fexactly for such a device at Amazon, which basically only has the measuring unit installed, but which has graphical displays on a normal computer. Unfortunately I only found one that was quite expensive on Amazon. Thanks for the link! I am sure you can see more with it.

Oh now Frank said it's not worth the money... 😅
 
Yes, tried that too. It is better, but not that better. One issue that is annoying is the slow USB and it's refresh rate (which is the same with both softwares) Then, the knobs and the "auto" settings are really bad.

@Wasserwiesel: Es lohnt sich ein bischen mehr auszugeben. Wirklich. Wär doch was zu Weihnachten
 
Only from the pictures, it really looks a lot better than the device I bought. But who knows...

Danke Frank, ich wünschte ich hätte ein besseres Gerät, aber für zweimal im Jahr mehrere hundert Euro auszugeben, dazu konnte ich mich noch nicht überreden. Mit graut es jetzt schon vor den Refreshraten von der Fischkiste. Naja dann gehts halt zurück.
Leider haben wir selbst in der Firma nur diese billigen tragbaren Geräte... Vielleicht besteht ja für nächstes Jahr Hoffnung, dass man sich über die Firma ein besseres bestellt. Stimmt schon, hätte ich eines hier, würden wir diese ganzen Gespräche hier nicht führen.
 
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