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Hi all,
If the PD has to limit the DC current at 720mA
max, there would be a hard current limit in the hot-swap of the PD chip at a
lower level, let's say 700mA.
This means that there will be less than 30W available
for the device, (700mA x 41V = 28.7W).
I think that we should put the PD DC current
limit above 720mA, to be sure the whole available power is supplied to
the load.
Thank you
Christian
From: owner-stds-802-3-poep@ieee.org [mailto:owner-stds-802-3-poep@ieee.org] On Behalf Of Anoop Vetteth (avetteth) Sent: Tuesday, June 26, 2007 5:10 PM To: STDS-802-3-POEP@listserv.ieee.org Subject: Re: [8023-POEP] IEEE 802.3at Vport ad hoc meetings Tuesday June 26; materials Hi Yair
Some more comments on your
presentation:
- Rather than having PSE Ilim_min = PD Ilim_max + 1mA; I
think it will be a cleaner solution to increase the Tlim_min for PSE from
50ms to 51ms (or 55ms to make it a round figure). My third point will make it
clear why I like this approach (This makes energy based policing
easy).
- I do not like the term Ilim_min for PSE. The whole
reason why we have current limiting at PD is so that we do not have to do
current limiting at the PSE. We need to come up with a better
name.
- In 802.3af we had Ilim_min/Icut_min = 14.28%. There is no
rational reason why we need to keep this ratio the same for 802.3at. We have
much more advanced processes today.
We need to come up with the minimum PD Ilim_max that is
acceptable to everyone. There is also no reason why we need
to specify that there be a maximum duty cycle of 5%. Even if we impose this, it
is highly unlikely that a PSE is going to check for 5% dutycycle over 1s. All we
care is the threshold and average current. If the PD draws more than Iport_dcmax
(720mA) for more than 51ms (or 55ms) then the PSE can shut off the PD.
There is no averaging involved here. This is a hard threshold as in AF -
Icut/Tcut
If the average current drawn by the PD over 1 second
is greater than Iport_dcmax (720mA) then the PSE can shut off the
PD.
Thank
you
Anoop
From: owner-stds-802-3-poep@ieee.org [mailto:owner-stds-802-3-poep@ieee.org] On Behalf Of Yair Darshan Sent: Tuesday, June 26, 2007 4:22 AM To: STDS-802-3-POEP@listserv.ieee.org Subject: Re: [8023-POEP] IEEE 802.3at Vport ad hoc meetings Tuesday June 26; materials Hi
Fred, Some
comments: Slide 4:
Icut_max/Icut_min is 0.4/0.3-1=14.28% and not 7% as
stated. Slide 5: I like the
simplicity of how PD is specified in 802.3af then how it presented in slide 5:
We should allow utilizing the full 29.5W as permited by the average current of
0.72A. We can do it easily by keeping the same concept and margins as in
802.3af. Having 14.28% margin between Icut_max to Icut_min allows
it. It is difficult to
understand slide 5. I disagree with the 1st bullet. We should allow
implementations that uses dc current with ac ripple within the range specified
between Icut_max to Icut_min limited to 50msec max and 5% duty as in
802.3af. Slide 6: The point of
having the current limit at the PD was to solve inrush current due to dv/dt in
PSE and dealing with long TLIM_MIN.
This slide suggests that PD with less then Cpd_max don’t have to implement
current limit. This was exactly the case in 802.3af so what is the purpose of
having all this PD current limit discussion? If Cpd is 179.9UF<180U then Tlim
_min may be still 12.6msec and we are back to square 1 = 3month
ago.. The solution is what I
thought last meeting: PD will limit the current within 1msec to ICUT_MAX so we
will have to charge only 0.12uF for the rest of the 50msec max of TCUT. See my
presentation that explains the whole thing. Slide 6: This slide is
relevant only if PD limits to Icut_min. which doesn’t support a solution to
utilizing max 29.5W. See my presentation for proposal to solve this
issue. In addition, please
allocate time to discuss my presentation that may help to solve some issues that
was supposed to be solved by moving the current limit to the PD and in my
opinion are still requires some discussion. The rest looks
fine. Yair From:
Hello, IEEE
802.3at, Vport ad hoc team meetings are scheduled for Tuesday June 26,
July 3, and July 10 (9 AM, PST) to cover current limits required for PoE. Please
review the direction we are heading at: http://grouper.ieee.org/groups/802/3/at/public/may07/schindler_5_28_07.pdf Please also
review: http://grouper.ieee.org/groups/802/3/at/public/may07/avetteth_0507.pdf Please
ensure that you review the IEEE-SA PatCom slides [ http://standards.ieee.org/board/pat/pat-slideset.pdf
] prior to the start of the conference call. At the start of call I will ask
that everybody confirms that they have read this material - if anybody hasn't we
will pause the call until they confirm that they have done
so. Thanks, Fred ______________________________________________________________________________ Frederick
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