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RE: detecting a PD disconnection event

Title: detecting a PD disconnection event
Comments inserted below.
-----Original Message-----
From: Rick Brooks [mailto:ribrooks@xxxxxxxxxxxxxxxxxx]
Sent: Friday, April 27, 2001 11:58 AM
To: stds-802-3-pwrviamdi@xxxxxxxx
Subject: detecting a PD disconnection event

Just to start up another discussion, I wanted to find out how many people would support
the following concept for detecting when a PD receiving power becomes disconnected.

the concept:

1) The PSE is responsible for detecting when a PD receiving DTE power becomes disconnected.
If that event occurs, the PSE must turn off the power within some time frame (100ms to 500ms ballpark?)
[Lynch, Brian] I think it should be 500ms or less. 

2) The PSE may use any of the following methods to detect this PD disconnect event.

        a) the DC load current drop below "X" ma (10ma?)

        b) the ethernet link has dropped out
[Lynch, Brian] I wonder if, in the near future, we see PDs that are not Ethernet devices at all. We are

creating a worldwide standard source for cheap, easy access, low power. We may see low power

battery chargers, emergency lighting, or whatever tapping into the port just for the power. 

        c) another proven method (pending discussion and feasibility proof)
                some suggestions:
                1) the AC probing circuit detects when the AC load changes (opens)
[Lynch, Brian] I would guess there would be detection issues in the midst of noisy environments, such as

an industrial site or manufacturing floor.
                2) the PD modulation heartbeat current ceases
[Lynch, Brian] If you are referring to the DC/DC converter, there may be a linear regulator there. 
                3) the PD response to a given PSE code is wrong or absent
[Lynch, Brian] Sounds like added circuitry in the PD 
                4) other ideas


Please voice your opinions on this concept.
The motivation here is to lower the cost of delivering DTE power.
[Lynch, Brian] I think the low current detection is the best one so far........... 

- Rick