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RE: [802.3af] RE: Startup and PD input cap


I realized that many of us have already shared the opinion about this issue.
For whatever it worth, I would like to pitch in my 2c here, too:

	1.  If we can make all the ports turn on simultaneously, why
necessitate the 8 sec wait?
	2.  Integrate 8 ports into a single IC seems like a good idea, but
why stop there?  How about 16 ports?
	3.  Putting a single 1J pulse  on an SO-8 package is marginal
(considering worst case ambient temperature).  Putting 8J on an IC limits
the package choice to only a few.  Putting 16J on an IC is out of the
	4.  System with multiple ports already has to struggle with size and
heat removal.  Adding 48J onto a 48 ports system is indeed quite a burden.
	5.  Having inrush limit PD ensures that the voltage at the terminal
of the PD will be well behave during power up.  It will simplify the
isolation switch's UVLO design.  I will also prevent the classification
current source from turning back on because the PD voltage will remain above

	I would vote for having both inrush limit on PSE and PD with the
inrush on the PSE is set higher than that in the PD.  This approach offers a
more predictable behavior in the PSE/PD interface and add to the robustness
of the standard.


Thong Huynh

> -----Original Message-----
> From:	Yair Darshan [SMTP:YairD@xxxxxxxxxxxxxx]
> Sent:	Friday, June 15, 2001 6:53 PM
> To:	'R karam'; Yair Darshan; 'Dave Dwelley'; 'Yair Darshan'; 'Karl
> Nakamura'; 'Donald S. Stewart'; 'Rick Brooks'; 'Lynch, Brian'; 'Peter
> Schwartz'; 'scott_burton@xxxxxxxxx'; 'Steve Carlson';
> 'rk@xxxxxxxxxxxxxxx'; 'mike_s_mccormack@xxxxxxxxxxx';
> 'bruce.inn@xxxxxxxxxx'; 'henryhinrichs@xxxxxxxxxxxx'; 'Jetzt, John J'
> Cc:	'stds-802-3-pwrviamdi@xxxxxxxx'
> Subject:	RE: [802.3af] RE: Startup and PD input cap 
> I was out for 4 hours and partying when I arrived again home I have
> noticed
> that you still around, so here it is..
> Roger the story here is very simple. No need to complicate it further and
> I
> believe that we can close it if we stick to engineering facts.
> In St Louis we have agreed as a compromise that the PSE will contain
> inrush
> current limiter and will be responsible to limit the current for PD input
> cap up to 50uF.
> And from 50uF and up the PD will be responsible for limiting the current.
> Right?
> I have told you and the others back than that 50uF is too low and all of
> us
> agreed that Dave and I will check again the number if we can increase it
> pending that integration in a chip is not impaired.
> I did it and the numbers confirmed by Dave and others.
> Now we can move the number from 50uF to 350uF(and still we have a lot of
> margin). Simple right? So what is the problem now? 
> As you told me in St Louis. If somebody will bring new and proven data we
> will change it right?
> In addition, see my comments below.
> Thanks 
> Yair.
> > -----Original Message-----
> > From:	R karam [SMTP:rkaram@xxxxxxxxx]
> > Sent:	ω, ιεπι 16, 2001 2:03 AM
> > To:	Yair Darshan; 'Dave Dwelley'; 'Yair Darshan'; 'Karl Nakamura';
> > 'Donald S. Stewart'; 'Rick Brooks'; 'Lynch, Brian'; 'Peter Schwartz';
> > 'scott_burton@xxxxxxxxx'; 'Steve Carlson'; 'rk@xxxxxxxxxxxxxxx';
> > 'mike_s_mccormack@xxxxxxxxxxx'; 'bruce.inn@xxxxxxxxxx';
> > 'henryhinrichs@xxxxxxxxxxxx'; 'Jetzt, John J'
> > Cc:	'stds-802-3-pwrviamdi@xxxxxxxx'
> > Subject:	Re: [802.3af] RE: Startup and PD input cap 
> > 
> > Yair
> > 
> > Now I thought you would be home partying by now, what are 
> > you still doing at work (laughs)
> > 
> > all right, I think the right answer may lie somewhere between Yair and a
> > bunch
> > of us who beleive in our own story, that is to Inrush in the PD or not
> to
> > inrush in the PD.
> 	[Yair Darshan]  I agree with the group that support inrush current
> limit in the PD for an input cap greater than TBD uF. Now we are arguing
> the
> number. We have calculated it and now the number is clear. 600uF is O.K.
> 350uF is proposed.
> > and so at the time I thought the 50uf was a compromise of live and let
> > live.
> 	[Yair Darshan]  With 350uF you let live for more PD vendors and I am
> not a PD vendor.......
> > So Yair wants that increased now (the capacitance) .  I think it would
> be
> > nice to find 
> > a way to  prove that we could setup a PD designer to fail without
> inrush-
> > or cause grief
> > of any kind.  
> 	[Yair Darshan]  I can give you a list of PD's without inrush
> limiting that was connected to a PSE with inrush limiting and they are
> working perfectly.
> 	I can give you a shorter list of PD's that was connected to PSE
> without inrush current limiter in the PSE and the results.
> > we can not test every possibility obviously (if this was a case of
> Yair's
> > Box or
> > mine -system and pd ) it would be easy, this is Yair's box and Mine vs
> the
> > rest of the world's PD's.
> > the big question is :
> 	[Yair Darshan]  Same as above.
> > can we think of a single case where we cause grief and grief is
> > interoperability problems like
> > Dave  was saying, failure to power up, oscillating) .... without inrush
> in
> > the PD, if we can set
> > up such a case prove it in the lab, then we may be done.
> 	[Yair Darshan]  As long as the PD designer will design according to
> his spec. Why he will face problems?
> 	If the PD designer will design PD with inrush current in it and will
> not obey the PD spec, he will face problem too right?
> > if I have enough time, I shall do some of this.  
> > so far I managed to repeat Rick's noise's measurements and we agree on
> > most of it,
> > there are some that require measuring (uv- common mode case) so the fun
> > never ends.
> > 
> > roger
> > 
> >