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Re: [802.3_4PPOE] MPS issue due to the allowance for reflected voltage in 3-pair mode



Hi Yair,

Your analysis is correct, the reverse current is added to the PDs own current.

I don't consider this an issue we need to do anything about however:
- it does not impair the primary function of MPS in any way (to remove power when the PD is disconnected)
- it only affects PDs that use the method of removing MPS in order to have the PSE remove power, I would say this is pretty rare;
- PDs that do want to have power removed can accomodate for the maximum 1.3mA of reverse current (draw less than 2.7mA of their own)

Note that reverse current only happens under 3-pair conditions, and then the 'must disconnect' current level is 4mA for PSEs.

Kind regards,

Lennart


On Mon, 2018-06-11 at 12:03 +0000, Yair Darshan wrote:

Hi all,

 

I found new problem that we need to discuss how to handle it.

 

In 3-pair mode during power on state, when a PD dont want to be powered, it generates e.g. MPS=1.9mA which means PSE must disconnect, but due to the PD that doesnt meet the backfeed on the unpowered pair, the unpowered pair consumes additional 1.3mA and this is added to the MPS. Under these conditions, the PD will not be disconnected.

Moreover, in general, a constant error of additional MPS current is added by the PSE..instead of PD only should control the MPS current.

 

Lets start to discuss this.

 

Yair

 

Darshan Yair

Chief R&D Engineer

Analog Mixed Signal Group

Microsemi Corporation

 

1 Hanagar St., P.O. Box 7220
Neve Ne'eman Industrial Zone
Hod Hasharon 45421, Israel
Tel:  +972-9-775-5100, EXT 210.

Cell: +972-54-4893019
Fax: +972-9-775-5111

 

E-mail: <mailto:ydarshan@xxxxxxxxxxxxx>.  

 

 


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