Re: IR2110 gate driver issues.

Terry Given wrote:

> Pooh Bear wrote:
> > Terry Given wrote:
> >
> >>Pooh Bear wrote:
> >>
> >>>Winfield Hill wrote:
> >>>
> >>>>Pooh Bear wrote...
> >>>>
> >>>>>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.
> >>>>
> >>>>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.
> >>>
> >>>
> >>>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.
> >>>
> >>>
> >>>>>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 *** does indeed show that
> >>>>>there's no connection. The low side drive activates at about 8V
> >>>>>and the high side about a volt higher.
> >>>>
> >>>>IR has to separately detect the low-side and high-side voltages,
> >>>>because the latter is the voltage across the flying capacitor.
> >>>
> >>>
> >>>True. I wish they'd OR the UVLOs though.
> >>>
> >>>
> >>>>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.
> >>>
> >>>
> >>>I'd prefer it if both terminated together !
> >>>
> >>>
> >>>>>Needless to say this creates 'issues'!
> >>>>>Anyone here used this part and care to comment?
> >>>>
> >>>>Let's hear about your issues.
> >>>
> >>>
> >>>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).
> >>>
> >>>
> >>>
> >>>>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.
> >>>
> >>>
> >>>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.
> >>
> >>
> >>what caps are you using for your bootstrap supplies?
> >
> >
> > Box polyester film. You gonna say I should be using ceramic ?
> >
> > Graham
>
> not until I read the data***. But I would caution against Z5U/Y5V,
> they are a path to temperature-related auto-self-destruct features.

No chance of me using shitty dielectrics !


> make sure there isnt too much ESR, the capacitance is stable with
> voltage & temperature, its happy with the peak current (maybe as high as
> Vboost/Rgate) and there is *** all inductance in the gatedrive loops.

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

> it can be a good idea with bootstrap supplies to use a couple of volts
> more than the lower supply, because of the load-dependant voltage drop
> across the lower switch (and, of course, the diode).

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

I'm erring towards local bootstrap supply now.

> I presume your diode is a fast HV diode.

MUR 460 in parallel with the switch. ~50ns


> I was once involved on the periphery with a cost-down of a small AC
> drive, 1% to 10% parts, that sort of thing. Changing the charge-pump
> gatedrive 100nF rectangular blue plastic film caps to cheap ceramic ones
> resulted in a 100% fatality rate on all 10 prototype units, about 20
> minutes into a thermal test. That change never made it to production.

I'm not gonna use cheap bits for this !


Regds, Graham

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