Is anyone familiar with the IR2304 MOSFET driver?

[Tom.G]

Be aware that the left two IC sockets are oriented wrong. The orientation notch is pointing downward in the photo putting pin one at the lower-right, but they are wired as if pin one is at the top-left.

The 0.2uF capacitors on pins 3&4 of the ICs are labeled as electrolytic, and their shiny body indicates they may be. I would expect them to be disc ceramic. Please verify they are correct per the original design, datasheet, or application note.

Of course we can't see the polarity markings on the caps, so double-check them before applying power. (they really stink with the wrong polarity, and sometimes emit sharpnel shrapnel)

Cheers,
Tom

p.s. the Fairchild 1N4148 is rated 200mA average current, probably fine.

 

[tim9000]

Be aware that the left two IC sockets are oriented wrong. The orientation notch is pointing downward in the photo putting pin one at the lower-right, but they are wired as if pin one is at the top-left.

The 0.2uF capacitors on pins 3&4 of the ICs are labeled as electrolytic, and their shiny body indicates they may be. I would expect them to be disc ceramic. Please verify they are correct per the original design, datasheet, or application note.

Of course we can't see the polarity markings on the caps, so double-check them before applying power. (they really stink with the wrong polarity, and sometimes emit sharpnel)

Cheers,
Tom

p.s. the Fairchild 1N4148 is rated 200mA average current, probably fine.

Woops, I didn't even notice the IC sockets had a notch! Thanks for pointing this out.

Also, apologies about the circuit diagram, it is out of date, are pins 3&4 Vcc and COM? (I don't have the datasheet on me at the moment). If so, this is a symptom of me needing to update the diagram, they are actually 1uF & 0.1uF tantalum and a smaller size ceramic capacitor. I can't remember if this was a specific requirement of capacitance across Vcc and COM, I assume it's enough.
I remember that some weeks ago I did a rough calculation (using the App note) for the capacitance across Vs and Vb and I concluded that 1uF & 0.1uF was enough, these are tantalum incidentally. I DIDN'T REALISE THESE WERE POLARISED, so they might be the wrong polarity. How can I tell? There are no markings and both the legs were equal in length.

P.S. Another thing I didn't realize until now is that tantalum caps were electrolytic, SO I HOPE THESE DON'T HAVE TOO MUCH LEAKAGE CURRENT...??

Cheers!

 

[Baluncore]

P.S. Another thing I didn't realize until now is that tantalum caps were electrolytic, SO I HOPE THESE DON'T HAVE TOO MUCH LEAKAGE CURRENT...??

Tantalum caps are polarised, with a solid tantalum oxide dielectric, so they do not have electrolyte and do not dry out. Cheap tants can have high leakage but reliably branded ones usually have low leakage.

 

[jim hardy]

In my day
dry tantalums were known for a propensity to pyrotechnics and good design included a small series resistor to limit surge current.
I think that's largely fixed today with polymer dielectric construction..
Wet tantalums didn't have that firebug tendency .

.https://www.digikey.com/eewiki/display/Motley/Tantalum+Capacitors

Because the composition and construction of a tantalum-MnO2 capacitor is similar to that of a firecracker (a finely divided metal in intimate mixture with a substance that releases oxygen when heated) these capacitors are well-known for failing in pyrotechnic fashion, characterized by explosions and/or violent spewings of flame. Particular care in their selection and application is recommended for this reason.

It's just one more monkey wrench in Murphy's toolbox.
If the smoke gets out of your capacitors that'd be something to look at.

Good Luck with this project.

 

[tim9000]

Tantalum caps are polarised, with a solid tantalum oxide dielectric, so they do not have electrolyte and do not dry out. Cheap tants can have high leakage but reliably branded ones usually have low leakage.

In my day
dry tantalums were known for a propensity to pyrotechnics and good design included a small series resistor to limit surge current.
I think that's largely fixed today with polymer dielectric construction..
Wet tantalums didn't have that firebug tendency .

.https://www.digikey.com/eewiki/display/Motley/Tantalum+CapacitorsIt's just one more monkey wrench in Murphy's toolbox.
If the smoke gets out of your capacitors that'd be something to look at.

Good Luck with this project.

My memory certainly failed in the interim of continuing this thread, so I just checked my purchases, and they are actually 1uF and 10uF "monolithic ceramic" capacitors, so I expect the coating is just superficially shiny like tantalum caps. And as I said, both the legs are equal in length, and there is no + or - markings, so I presume they're bipolar. Any contrary opinions, please let me know.

So hopefully (when I have some spare time), I'll be able to move onto the next phase of the project and integrate the MOSFETS to this board, and connect the Halls and Pi.

Unless anyone sees any other issues.

Thanks all!

 

[Tom.G]

are pins 3&4 Vcc and COM?

Yes (at least so says the datasheet )

 

[tim9000]

Yes (at least so says the datasheet )

Cool.

Well, I'll probably be back on this thread in a couple months when I have an update. I am moving inter-state to start a new job, so don't hold your breath in wait.

Cheers

 

[Tom.G]

Enjoy the new scenery wherever you end up.

Cheers!

 

[jim hardy]

Good luck in new enterprise. Hopefully they'll apprentice you to an old timer expert for a mentor. Best thing that ever happened to me.

 

[tim9000]

Hi All,

I'm trying to get back on this horse, this thread hopefully isn't dead yet. To refresh you're memory this was a brushless DC motor to be run from 36V lithium batteries. The controller between the bldc hall sensors and MOSFET drivers was a raspberry pi.

(So I've been getting smashed at my new job, 11 & 1/2 hour days during the week and working on the house on weekends. I've been having to do not just design engineering at work but also because it's a new-ish company also the QAQC, [most of the] draughting developing all the system processes like testing, manufacturing ITPs, drawing conventions/register etc. etc. ...Also, we have our 3rd child on the way!)

I've been trying to find all my project notes since moving house and I think I've more or less found everything to resume the project.

To re-cap where I'm at, from memory from six months ago (hazy):

-Despite being an inductive load (bldc motor) I was going to forego the schottkey diodes in parallel with the mosfets and see if the internal body diodes can handle the flyback current. (Otherwise I'll use 1N4148 diodes. These apparently have a reverse recovery time of 8 ns and a 100V breakdown voltage.)

-There was previously an issue of me possibly not firing the Lo for the Vb capacitor to charge up.

-I was using the of the IR2304 gate driver and I'd already made my circuit board to house them. So due to time constraints I would still like to use this driver, sacrificing fast switching time for something that still 'just does the job'.

-The input capacitance of the previous MOSFETs was 3247 pF which we concluded would not be suitable for the IR2304 to be able to drive. I now want to use an NMOS with an input capacitance of 920pF (the F40NF06). I am hoping that this will make up for the low pulse current (60mA) of the IR2304).

Can someone please advise if these conditions are going to be an obvious non-starter. Failing this I will have to use the IR2301 (120mA) gate driver and make a new circuit board and re-code so it creates and artificial anti shoot-through on switching.

Thank you

 

[Baluncore]

(Otherwise I'll use 1N4148 diodes. These apparently have a reverse recovery time of 8 ns and a 100V breakdown voltage.)

But they are signal diodes, not power diodes. The peak MOSFET current will flow through the 1N4148 momentarily. You need to use the integrated body diode, or an external fast recovery diode rated for repeated pulses of Imax.

 

[tim9000]

But they are signal diodes, not power diodes. The peak MOSFET current will flow through the 1N4148 momentarily. You need to use the integrated body diode, or an external fast recovery diode rated for repeated pulses of Imax.

My mistake, if the integrated body diode is insufficient for the motor freewheeling current, I won't use a small signal diode, it will be a power fast recovery diode. I must have misinterpreted my component notes, the 1N4148 must have been for something else.

 

[Tom.G]

I now want to use an NMOS with an input capacitance of 920pF (the F40NF06). I am hoping that this will make up for the low pulse current (60mA) of the IR2304).

I haven't gone back and reviewed the earlier stuff but the you may want to check the dissipation during the rise & fall times. Here is a quick estimate of those times.

Assume
Vg = 10V
Cg = 1E-9F
Ig = 6e-2A

T= (dVg x C)/Ig
= (10 x 1E-9)/6e-2
=1.6E-7
=160ηS rise and fall times.
Looks plenty fast enough!

With the delays and slew rate of the the Gate driver and the FET adding up to around 1.7uS you should be good to 100kHz switching frequency, depending on motor current.

Cheers,
Tom

 

[tim9000]

I haven't gone back and reviewed the earlier stuff but the you may want to check the dissipation during the rise & fall times. Here is a quick estimate of those times.

Assume
Vg = 10V
Cg = 1E-9F
Ig = 6e-2A

T= (dVg x C)/Ig
= (10 x 1E-9)/6e-2
=1.6E-7
=160ηS rise and fall times.
Looks plenty fast enough!

With the delays and slew rate of the the Gate driver and the FET adding up to around 1.7uS you should be good to 100kHz switching frequency, depending on motor current.

Cheers,
Tom

Hi Tom,

Very simple but effective way of calculating the charging time of the gate capacitance, thank you for showing me that.

Out of interest, on the MOSFET datasheet Table 5 when they state:

td(on) = 27 ns and tr Turn-on Delay Time Rise Time = 11 ns
Using test: VDD = 30V, ID = 20A, RG = 4.7Ω, VGS = 10V

What sort of a driver would they have used to get these results would you speculate?

Cheers,

 

[Tom.G]

What sort of a driver would they have used to get these results would you speculate?

That is documented in Fig. 18 of the datasheet available at:
https://www.st.com/resource/en/datasheet/stf40nf06.pdf
Hmm... can't get the image to upload. It's on pg.8 of the datasheet

Cheers,
Tom

 

[tim9000]

That is documented in Fig. 18 of the datasheet available at:
https://www.st.com/resource/en/datasheet/stf40nf06.pdf
Hmm... can't get the image to upload. It's on pg.8 of the datasheet

Cheers,
Tom

Sorry, I just wasted your time. Thank you for not barrating me for asking a stupid question. I'm going to guess it was some sort of 10V power supply with a really low internal impedance. I'm guessing not battery though... possibly capacitor bank.

Thanks, I'll post on here next time I have some results to update the thread with (please don't hold your breath).

Take care.