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RE: [802.3af] Clarification- to the propose text



Roger,
You are correct with your analysis when PSE is connected to an other PSE.
And as the standard specified today we don't need special circuits to handle this situation.
Yair.
 
-----Original Message-----
From: Roger Karam [mailto:rkaram@xxxxxxxxx]
Sent: Tuesday, January 14, 2003 9:28 PM
To: stds-802-3-pwrviamdi@xxxxxxxxxxxxxxxxxx
Subject: [802.3af] Clarification- to the propose text

Hi

here is a clarification to the proposed text:

I propose we tell designers to test their PSE and their PD both
to a  'Hot'  PSE - (opposite And same polarity) and be done with this.
so here is the text:

"The PSE must tolerate the application of a voltage of  the same and of  opposite polarity (up to 57v)
From another PSE*
without incurring any damage when such potentials are applied for an indefinite amount of time."


* cause that PSE would be current limited to a max of 450ma and we assume is to be shut off.
  here we may choose to use a non PSE test when PICS is written....
   so the 'other' PSE may be a power supply with a limited current of 450ma...

reasons:

some vendors (chips and system) already have put together hardware
with opposite polarity to what we all agree to, and feel like we do not have
the right thing going here.

also for such a scenario to take place the following has to happen:

1- Both PSE's must fault (not discover before powering) or both be ' HOT '.
we worked hard to insure this does not happen --in af.

2- We have a parallel diode that we specd (paid for) at the PSE end that takes care
of a hot-plug the current can return to the originating PSE.
At the same time the diode helps a PSE discriminate by polluting anything in the other PSE
that resembles a signature insuring no false discovery of another PSE.... No Hope here this
better be reality or we are in bad shape.

3- Even with all PSEs following a single polarity a cross over cable would take us back
to the same problem again?!- if the PSEs are Hot - what am i missing.

That was my 2c for today,
roger



Hi

I propose we tell designers to test their PSE and their PD both
to the 'Hot' - Opposite polarity and be done with this.
so here is the text:

The PSE must tolerate the application of a voltage of equal and opposite polarity to its
own without incurring any damage when such potentials are applied for an indefinite amount of time.

reason:

some vendors (chips and system) already have put together hardware
with opposite polarity to what we all agree to, and feel like we do not have
the right thing going here.

also for such a scenario to take place the following has to happen:

1- Both PSE's must fault (not discover before powering) or both be ' HOT '.
we worked hard to insure this does not happen --in af.

2- We have a parallel diode that we specd (paid for) at the PSE end that takes care
of a hot-plug the current can return to the originating PSE.
At the same time the diode helps a PSE discriminate by polluting anything in the other PSE
that resembles a signature insuring no false discovery of another PSE.... No Hope here this
better be reality or we are in bad shape.

3- Even with all PSEs following a single polarity a cross over cable would take us back
to the same problem again?!- if the PSEs are Hot - what am i missing.

That was my 2c for today,
roger