IR2110 gate driver issues.

Device failure meaning damaged components, or meaning, a FET that didn't do what you expected under a certain circumstance, but yet wasn't actually damaged.

IR has to separately detect the low-side and high-side voltages, because the latter is the voltage across the flying capacitor.

The mismatch you observed sounds good: the high side should stop working well before the low side, thereby preventing any shoothro current, which could be disasterous.

Let's hear about your issues.

BTW, recognizing the need for low-voltage protection, and the need for a benign response to low-voltage conditions, you could easily add a comparator operating at lower voltages, plus shutoff gates managing the IR2110's three logic inputs, per your special needs.

--
 Thanks,
    - Win
Reply to
Winfield Hill
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Graham, you're way ahead of us. But the real issue is what the actual operating modes are and their etiologies. We'll discuss that pursuant to your other response.

--
 Thanks,
    - Win
Reply to
Winfield Hill

Hi all,

I'm using an IR2110 high and low side gate driver in a smps that I mentioned some time back in the group under the thread 'should I use a SG3525'.

I've had some 'odd' power device failures that I didn't expect in entirely benign situations, such as the half bridge output simply driving the primary of my transformer.

I realised that it happened a couple of times when I wound down the input volts ( I'm supplying the board via a variac and isolating transfomer for development ).

The IR2110 has undervoltage lockout. Fine ! I checked it carefully today and the UVLO for the low side and high side aren't linked. Indeed a careful look at the data sheet does indeed show that there's no connection. The low side drive activates at about 8V and the high side about a volt higher.

Needless to say this creates 'issues' !

Anyone here used this part and care to comment ?

Regds, Graham

Reply to
Pooh Bear

Hey Poop, What is this, Electronics 101! Sure these parts are old enought. You should worry about electromigration. The SG3525A has UVLO at about 7VDC and locks it's outputs low. Make sure it goes down before the IR2110. YMMV with the SG3525.

Harry

Reply to
Harry Dellamano

Hello Winfield,

Or use a TLV431 for UVLO purposes. They are pretty accurate and cheap.

Regards, Joerg

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Reply to
Joerg

LOL !

The 3525 isn't the prob - it does indeed UVLO around 7V and has 300mV of hysteresis.

The 2110 low side UVLO appears to be @ 8V and the high side @ around 8.9V. So as the power rails sag the high side device stops conducting but the low side doesn't. Interesting. Doesn't appear to be any hysteresis on the 2110 either.

I reckon I'm going to have to implement my own undervoltage lock out to stop the

3525 @ about 10V.

Just curious if anyone else had noticed this.

Choice of devices was partly determined / influenced by their use by the major US manufacturer of pro-audio amplifiers in a similar application.

Graham

Reply to
Pooh Bear

Device going short. Either just the high side device or both. I've established to my satisfaction that there are 2 failure scenarios.

  1. Ramping the voltage down on the variac ( quickly ) . E.g. after I've been testing @ line voltage. There's a bzzt and the high side device goes short. I suspect a mixture of the UVLO mismatches and possible 'mis-track' of the main bus and supervisory rail. Doesn't happen if I ramp the volts down slowly ( or so it seems ). Hence my thoughts about the droop of the rails.
  2. Both devices fail - this first happened after I'd been running the transformer primary only for about 1/2 hour just to establish likely practical core temp rise. It ran fine for ages - I turned my back to do some calcs and the thing bzzt'ed at me. It was still working so I thought I was hearing things ! Did it terminally 3 mins later. Looking closely I'm seeing the high side drive terminate prematurely under circumstances I have yet to exactly determine the cause of. Maybe insufficient bootstrap C ? Was looking at this last thing today. Will investigate further tomorrow wrt all the drive waveforms.

True. I wish they'd OR the UVLOs though.

I'd prefer it if both terminated together !

Well, the devices failing for one !

The 2110 UVLO is sensitive to line ripple. It appears to result in a effect that's like weird duty cycles when it's hovering around the UVLO threshold(s).

That's what I imagine I may indeed have to do. Or I can shutdown the

3525.

Was curious if anyone had experienced similar when using the 2110.

Cheers, Graham

p.s. I now understand why smps design has always had a reputation for being 'tricky'. Also why when quizzed about them - some vendors go all shy when talking about the reliability of smps versions of their audio amps ! I have no plans to put anything into production that's marginal.

Reply to
Pooh Bear

Guess what I sketched late this afternoon ! With an LM393. It may be wise to OR my own UVLO on both supervisory and main bus rails.

Graham

Reply to
Pooh Bear

Thank you for kind response.

I'm especially interested in what's causing the premature termination ( under certain circumstances ) of the high side drive. At one point just poking the probe of a Fluke 77 on the Vboot pin caused the effect ! At times like this 4 channel scopes ( and diff amps ) are a really attractive proposition.

The UVLO issue seems like a trivial one in comparison. Just surprised that I haven't seen similar measures in other commercial designs I've looked at.

Graham

Reply to
Pooh Bear

Box polyester film. You gonna say I should be using ceramic ?

Graham

Reply to
Pooh Bear

For you maybe !

Have I seen your name on any ABs I may have read btw ? I'm thinking maybe Unitrode ?

Graham

Reply to
Pooh Bear

Your thinking of my brother, Robert Mammano, the original designer of the SG3525 at Silicon General. Now I believe semi retired with TI-Unitrode. I'm still in El-101. cheers, Harry

Reply to
Harry Dellamano

Pooh, you should see how the charge pump works. By conducting the low side FET, the bootstrap capacitor gets charged, just the same happens when the device comes on. Then, when the voltage is sufficient, the device works as advertized. When you have it too long high, the droop will be enough to trigger the undervoltage and the device goes low again, to allow the charging of the cap. So it is made to work well on a full bridge. On a half bridge a DC component will result, which is a problem with your transformer. So either you increase the value of the cap, or you drop the chargepump all together and aliment the upper leg with a separate floating PS, or make a full-bridge with another driver and use lower supply voltage or a different transformer. Maybe your transformer is not pulled down completely because of too high resistance of the FET or the current shunt, or the 12V auxiliary voltage is too low?

--
ciao Ban
Bordighera, Italy
Reply to
Ban

I think you're going down the wrong track. If a FET fails to turn on because of an activated UV lockout, this should not be the cause of a MOSFET short. What would be the mechanism for that? Yes, the desired switching function is interrupted, but benignly so.

I suspect you have a different common and deadly problem, namely fast MOSFET source-voltage spikes from reverse-recovery-time snapoff. This occurs if the FET's intrinsic body diode conducts, and the ns spikes can damage the FET's delicate gate insulation. V = L di/dt where L is your FET's source-lead inductance, and the di/dt is high because dt can be under 1ns during t_rr snapoff.

The FET diode's will clamp the flyback from your transformer's leakage inductance if during the delay after the other FET turns off the flyback voltage swing is high enough. This clamping with the resultant spike will happen if you have an inadequate snubbing network across the FETs to prevent the flyback from swinging across your entire raw dc voltage supply. The snubber network can simply be a drain-source capacitor, to absorb the leakage-inductance energy or it can be more complex. But whatever your choice, don't ever let the FET's body diodes conduct!!!

Note, the transformer's leakage-inductance energy is proportional to current, which means it's flyback effect is minimal under no load, and worst under full load. Carefully examine your switching waveforms to see how they change as you increase the load on the transformer output.

As I said, while disconcerting, it shouldn't take out MOSFETs.

BTW, did you tell us what FETs you're using? And tell us more about your transformer and the operating voltages and currents. Did you measure the transformer's leakage inductance?

It takes an experienced designer to make a reliable switcher.

--
 Thanks,
    - Win
Reply to
Winfield Hill

Yes that rings bells.

Thanks for your input Harry. It's always appreciated.

Graham

Reply to
Pooh Bear

Yes.

Should not happen if Cboot is large enough. This is something to be checked.

For sure !

Agreed. Will investigate this next !

IR have an app note regarding low frequency operation of the low / high side drivers that uses a separate charge pump entirely. I am inclined to look at this route.

No. Damn good FETs or IGBTs. Vce sat = 2 V max. Lower for FETs.

The aux supply is good - around 14V @ variac with max setting.

I suspect there's something I'm missing. I dare say it will 'come out in the wash' ! This will be interesting !

Thanks, Graham

Reply to
Pooh Bear

That's the STP11NM60FD, right? Not to be confused with ST's _FP parts, which are insulated packages. The STP11NM60FPFD is OK. :>)

Like I was saying, don't let these FET diodes conduct. But if they must conduct, a fast diode that reduces the current buildup in the leakage inductance before the current snapoff helps a lot. There are also soft-recovery-diode types that one can use.

--
 Thanks,
    - Win
Reply to
Winfield Hill

No chance of me using shitty dielectrics !

Tried to minimise the gate drive tracks and indeed all fast tracks but I reckon my layout man could have done a little better.

Hmmm........ typical bootstrap operation results in a diode drop plus device Vce or Vds drop.

I'm erring towards local bootstrap supply now.

MUR 460 in parallel with the switch. ~50ns

I'm not gonna use cheap bits for this !

Regds, Graham

Reply to
Pooh Bear

Add a electrolytic of some sort for long term hold up if the high sides are going to be on for a while.

I don't see whyhaving the FETs turn off when the power goes low is an issue though. Hmm, unless they are oscillating on/off at high frequency as the power is sagging. I didn't think the 2110s were prone to that but...

Robert

Reply to
R Adsett

what caps are you using for your bootstrap supplies?

Cheers Terry

Reply to
Terry Given

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