Heath, your review includes this statement: Moving the PD requirement to the PSE is onerous and moves requirements from the out-of-spec PD to the compliant PSE.
I disagree with this statement. This is not an out of spec PD. The PD 100% complies to the backfeed spec as written in Clause 33. We carried forward that requirement simply because we copied 33. As I’ve said repeatedly, the backfeed requirement
is a true 2P requirement. When you apply 3P power, you are not performing this test and the requirement no longer applies. The real first question we should have asked is does a true 2P test belong in a 4P standard.
This is no longer simply a ‘FET bridge’ problem. It’s been reported on this reflector that schottky diodes also fail the misapplied 3P backfeed test. The PD is only “misbehaving” because the PSE is improperly applying 3P power. If you want
to outlaw this behavior, then you are mandating silicon diodes. This standard fails if that is a requirement.
This is a PSE misbehavior that we decided to make compliant. The PSE holds the burden to fix.
Chad Jones
Tech Lead, Cisco Systems
Chair, IEEE P802.3bt 4PPoE Task Force
Principal, NFPA 70 CMP3
From: "Stewart, Heath" <Heath.Stewart@xxxxxxxxxx>
Reply-To: "Stewart, Heath" <Heath.Stewart@xxxxxxxxxx>
Date: Thursday, May 10, 2018 at 8:24 PM
To: 4PPOE Reflector <STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_4PPOE] Backfeed presentation + baseline
As always we appreciate your ongoing work. We continue to have some concerns regarding the PSE requirements. As written they do are in effect during 4-pair power operation (and at all other times,
without limit.)
We consider a PD which presents a reflected voltage (above Vrefl) during classification to be undesirable. As such we have marked up your presentation to suggest some changes.
Cheers,
-Heath
From: Lennart Yseboodt [mailto:lennart.yseboodt@xxxxxxxxxxx]
Sent: Thursday, May 10, 2018 10:15 AM
To: lennart.yseboodt@xxxxxxxxxxx; Stewart, Heath <Heath.Stewart@xxxxxxxxxx>; STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Backfeed presentation + baseline
Hi Heath,
v220 and v230 correspond to both approaches we discussed during the adhoc call.
At the end of the call, I believe the consensus was to split Irev into two values (for >21V and <21V), which corresponds with v230.
Overview:
v220
- PSE requirement Irev is 1.3mA and applies when applying 2-pair (=3-pair) power on the unpowered negative
- PD has to safeguard classification, hence has a 3P-backfeed requirement from 0-21V
v230
- PSE requirement is split into 500uA when highest pairset voltage <21V and 1.3mA when highest pairset voltage >21V
- Because the PSE has a current limit that does not corrupt classifcation in the classification range, the PD is only required to limit 3P-backfeed in the detection range
0-10.1V
The advantage of v230 is that it allows for wider implementation of PD bridges.
Kind regards,
Lennart
On Thu, 2018-05-10 at 16:05 +0000, Stewart, Heath wrote:
Lennart,
Version 220 showed 21V. This version shows 10.1V. Can you comment?
Heath Stewart
Design Center ManagerPoE/PoDL Products
Cell (805) 895-0499
Office (805) 560-7658
Websites analog.com, linear.com
Linear Technology is now part of Analog Devices. Learn more.
From: Lennart Yseboodt [mailto:lennart.yseboodt@xxxxxxxxxxx]
Sent: Wednesday, May 9, 2018 12:49 PM
To: STDS-802-3-4PPOE@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3_4PPOE] Backfeed presentation + baseline
Updated as discussed during the meeting, this is version 230.
On Mon, 2018-05-07 at 20:40 +0000, Lennart Yseboodt wrote:
Hi all,
As presented today. I’m currently updating the text based on the feedback I got.
Kind regards,
Lennart
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