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

[Yair Darshan <YairD@powerdsine.com>]

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@cisco.com]
> 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@mitel.com'; 'Steve Carlson'; 'rk@design.mxim.com';
> 'mike_s_mccormack@ne.3com.com'; 'bruce.inn@micrel.com';
> 'henryhinrichs@pulseeng.com'; 'Jetzt, John J'
> Cc:	'stds-802-3-pwrviamdi@ieee.org'
> 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
> 
>