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Re: [8023-POEP] IEEE 802.3at Vport ad hoc meetings Tuesday June 26; materials




Christian:  I think that it would be prudent to wait for TIA TR-42 and UL to come back with recommendations
on the maximum current(s) in single cables and bundles before debating the current limit(s).
You may be all debating limits above operating conditions deemed safe by experts in that field.

Best Regards

P.S  Frankly the current limits this TF is discussing concern me.
When I look at the way big bundles of CAT5/6 are crammed into some buildings,
Imagining all of them carrying the maximum current supplying Powered Devices,
leads me to a "Hindenburg Scenario" or "Tacoma Narrows Bridge Syndrome"
caused by all those videos I was forced to watch in Engineering Classes with
the not so subtle message: This is what happens when engineers screw up.


Maurice Reintjes
MindspeedTM
Hillsboro, Oregon,USA
Office Phone (503)-403-5370
Mobile (503)-701-0797



Christian BEIA <christian.beia@ST.COM>
Sent by: owner-stds-802-3-poep@ieee.org

06/26/2007 09:07 AM
Please respond to
Christian BEIA <christian.beia@ST.COM>

To
STDS-802-3-POEP@listserv.ieee.org
cc
Subject
Re: [8023-POEP] IEEE 802.3at Vport ad hoc meetings Tuesday June 26; materials





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: Fred Schindler (frs) [mailto:frs@cisco.com]
Sent:
Tuesday, June 26, 2007 3:58 AM
To:
STDS-802-3-POEP@listserv.ieee.org; Parker, Tim (SC100:321); Andrew Smith; Wael Diab; mike@akrossilicon.com; Hugh Barrass (hbarrass); david_lucia@sifos.com; sajol@sbcglobal.net; Dove, Dan; keith@phihongusa.com; Dinh, Thuyen; Patoka, Martin; Daniel Feldman; Yair Darshan; Anoop Vetteth (avetteth); Clay Stanford; Matthew Landry; David_Law@3com.com; Krellner Jan-r35458; david@akrossilicon.com; Riccardo RUSSO; Huynh, Thong; Youhao Xi; McCormack, Michael; Bill Delveaux (bdelveau); Pavlick Rimboim; Chad Jones (cmjones); Sanita Gianluca; Shinkyo, Kaku; Joseph Maggiolino; Taylor, Rick; Brian Buckmeier; Soe, Myat Myitzu; Unterdorfer, Pascal; EVM(Elsa Madrigal); christian.beia@st.com
Cc:
Fred Schindler (frs)
Subject:
IEEE 802.3at Vport ad hoc meetings Tuesday June 26; materials

 
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
 
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Fred Schindler
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