Re: IR2110 gate driver issues.

Pooh Bear wrote: 
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 ! 

didnt think so. I should have replaced "But" with "if you said ceramic"

I asked this question a while back, but no-one rose to the challenge: is there *any* application in which its worth using Z5U/Y5V? every time I check, the voltage and temperature coefficients mean an X7R cap provides far more capacitance in the same footprint, at the same cost.





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.


I do the layouts myself. far easier.



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.

yep. dont forget to check your diode forward recovery time as well. that can bite a chunk off your supply.

I had to solve a non-regulating flyback supply once (with TL431 + opto feedback) that in large part was due to the use of a seriously *** diode for a rectifier (I forget which diode, almost 1N400x type, Trr was a us or two). I had worked on some of the designers other stuff, didnt recognise the part number so just assumed he would use a suitable part. there were other serious problems too, but the diode made me waste a few days. both forward and reverse recovery were problematic.

It became a production problem because the output voltage just happened to be right (ish, calibrate on test) when fed from 115Vac. problem was it was a universal ac input ups battery charger, and batteries started dying.....


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

que? bootstrap diode (havent read IR2110 data ***, it may include them) from -Vdc bias supply to flating supply, cap to E[S], current flows when lower switch turns on.




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 !

I later designed the gatedrive for the replacement product, used a similar idea but with a much better gatedrive circuit, and X7R caps. It was then that I really learned my dielectrics, when a supply drooped about 20x faster than it ought to (20V bias on 25V Z5U cap). At that point I also answered the "why did the last product die" question, which was never really investigated at the time - those involved simply went "ok, dont change them" and moved on. We did a quick test with the old product using X7R caps, and it worked like a charm.



Regds,        Graham


Cheers
Terry
.