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UC3710 gate drivers keep turning off.

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Marko

Sat Mar 08 2008, 06:30PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

These have caused me a great deal of frustration through last month.

I badly needed gate drivers in package which can be heatsinked decently, and TO220 versions of these were only such available to me.

To cut the long story short, these drivers seem to spontaneously turn off for some reason, latching the output to low and holding it such no matter of the input state, until power is cycled! - I hope you guys get what I mean.

I have two of these drivers driving a GDT, with constant input signal from a signal generator - if I remove the signal for a short time, and put it back, one driver goes ''off''!
This results in amplitude of output signal being halved - something very bad for the mosfet bridge!

After 'cycling' the input signal for a while like that, the other driver goes off too, and only thing left for me to do is cycle the power!

I have the inverting input tied to ground all the time, and using the non-inverting one for input.

At outputs I'm using clamping diode pairs, DC block cap and 1ohm resistor in series with GDT primary.

This is absolutely frustrating as I don't know of any more variables I could try out.

Only thing I noticed is, that driver sometimes 'restarts' if there is a 100ohm resistor parallel with DC blocking cap, need to investigate that more.

Device has protection systems built in:

UVLO - I really don't know any way it could permanently turn off the device;

Thermal shutdown: problem happens at any temperature and without load at all, something would have to go terribly wrong with it.

Anyone of you guys can explain me how to use these devices properly? I'm really clueless now, it looks like I'm going to have to find some IXDD414's or 442*'s in power packages

Thanks,

Marko

Dr. Dark Current

Sat Mar 08 2008, 06:33PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Sorry no idea as to your problem, but you can get samples of TC442x's in TO220-5 packages. I have 6 of them lying in front of me on the table right now.

Marko

Sat Mar 08 2008, 06:40PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

jmartis wrote ...

Sorry no idea as to your problem, but you can get samples of TC442x's in TO220-5 packages. I have 6 of them lying in front of me on the table right now.

Microchip didn't want to ship to me - It's pretty hard to get samples in croatia.

It seems that ebay is cheapest option left even after huge shipping fee, unless somebody nearby has a large lot and it wishing to sell some to me, but I hope not to come to that.

I'd much rather like to find out how to use devices I already have

,

Marko

PS. I'm now sure this happens only with GDT, not with direct drive. I'm not sure what is the difference, free wheeling diodes don't seem to do anything.

HV Enthusiast

Sat Mar 08 2008, 10:33PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Make sure you have adequate bypass capacitance. Have at least a 0.1uF ceramic and a large 10uF tantalum right at the Vcc of the pins.

Marko

Sat Mar 08 2008, 10:53PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

EastVoltResearch wrote ...

Make sure you have adequate bypass capacitance. Have at least a 0.1uF ceramic and a large 10uF tantalum right at the Vcc of the pins.

Yes I have decoupling caps EVR, sorry for not mentioning it.

Drivers seem to be latching only under inductive load of the GDT.

I really don't know what to blame for it, ideas are depleted for now.
I'd be very glad if anyone could explain how could something like this happen, freewheeling diodes block nearly all of overvolage caused by ringing.

Oh, and can post some pics if anyone wishes.

Tomorrow,

Marko

HV Enthusiast

Sun Mar 09 2008, 12:15AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

What voltage are you running at?

These chips feature under voltage lock-out (UVLO). I'd hook up a scope to monitor the voltage at Vcc right at the pin of the package. See if it dips below the UVLO voltage.

Thermal shutdown???

Did you try replacing the chip. Could be a bad chip too.

Dan

Marko

Sun Mar 09 2008, 11:45AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I'm running the drivers off 12V. Not really close neither to max rating or UVLO trip which is at 4.7V. It's pretty stable with all the decoupling I have, I can't notice any ripple on the scope.

I have six of these devices here and all seem to work very well into a direct capacitive load, but they start latching up randomly with a GDT.

At power up, they work and GDT gives a pretty nice output signal, even when I load it with mosfets (really doesn't look like malfunction), but if I disconnect the signal from the antenna at least one driver shuts off and when I put it back I get half of the output voltage I had before.
Or just both go off.

I really hoped somebody used these particular IC's had got around similar problems...

Dalus

Sun Mar 09 2008, 01:44PM

Registered Member #639 Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512

Are you using clamping diodes?

Marko

Sun Mar 09 2008, 02:25PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Dalus wrote ...

Are you using clamping diodes?

Yes dalus. As far as of now, drivers seem to latch up both with Schottky's and 4148's.

I recall some of you guys were talking about differences between Schottky and normal fast diodes used as freewheeling diodes on gate drivers, but really I don't understand it?

I think someone mentioned it for UCC's, that Schottky's are better if my supply voltage is very close to max rating?

*PS*:

Ok I was definitely wrong - I replaced the 4148 diodes with schottky and drivers worked well.

Good thing it works but bad thing is that now again I don't have a clue why didn't my recent board which always used schottky diodes work.

So, can anyone explain what's really happening? What really causes ''latchup'' in bipolar devices?

I don't understand what particular difference do those few hundred milivolts of drop make.

What exactly happens to cause latchup?

As far as I know, the capacitive load on the output acts like a short for the transformer, so only the energy trapped in leakage inductance (which is very small) can get back to the driver.

I've used discrete transistors and SG3525 output stages without any diodes, and they never latched up, only some more ringing would show up.

Marko

Marko

Sun Mar 16 2008, 06:47PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Schottky diodes at first seemed to have solved the problem pretty well. I put the UC3710's into a control circuit and ran a small halfbridge SSTC very well up to 17 cm sparks, never expeirenced any problems.

After I move the circuit into double fullbridge coil problems started again, gate drivers seem to be latching up again. They have Schottky freewheeling diodes and everything from before.

This is now pretty defeating for me.

Please, does *anyone* know why would gate drivers care so much for few hundred millivolts of additional drop on their freewheeling diodes?

I do not understand what mechanism can cause this ''latchup'' effect or whatever, apparently in output stage?

What can cause a bipolar transistor to latch up in any circumstances?

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