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RE: detecting a PD disconnection event


For 1) The PSE should disconnect power from the port within 400mSec.
          Reason: Lab tests shows that fast technician can not disconnect PD
with non-PD device and cause damage.
          It is also suggested that within this time, the average port
voltage will be 5V max. (to limit PSE output port capacitor energy) 

For 2) The easiest way is to measure the current and disconnect the port
voltage if the current is less than 10mA for more than TBD msec.
          Actually the PSE should disconnect in less than 5mA, and may or
may not disconnect between 5 to 10mA. These values allows simple sensing
          which we need any way for the overload protection.

         The other method like checking the Ethernet link has few drawbacks:
         1. It can not be supported by Midspan.
         2. What will happen if the PD is connected to external source
voltage and you still have link, however the PSE is still delivering power
and it should not.

See more comments below.


> -----Original Message-----
> From:	Rick Brooks [SMTP:ribrooks@xxxxxxxxxxxxxxxxxx]
> Sent:	ו, אפריל 27, 2001 5:58 PM
> 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?) 
> 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?) 
	[Yair Darshan]  See above.

>         b) the ethernet link has dropped out 
	[Yair Darshan]  See above.

>         c) another proven method (pending discussion and feasibility
> proof) 
>                 some suggestions: 
>                 1) the AC probing circuit detects when the AC load changes
> (opens) 
	[Yair Darshan]  It is sensitive to noise. DC methods are more
>                 2) the PD modulation heartbeat current ceases 
	[Yair Darshan]  Not clear?
>                 3) the PD response to a given PSE code is wrong or absent 
	[Yair Darshan]  This is related to false detection, and we need some
thing unique for disconnecting.
>                 4) other ideas 
> $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ 
> Please voice your opinions on this concept. 
> The motivation here is to lower the cost of delivering DTE power. 
> thanks, 
> - Rick