|Thread Links||Date Links|
|Thread Prev||Thread Next||Thread Index||Date Prev||Date Next||Date Index|
I would like to discuss the benefits in mandating diode bridge at the input of both data pairs and spare pairs.
The PD is required to be ready to accept power from the spare pairs or from the data pairs.
Typical implementation of Oring the power from data pairs or spare pairs could be one of the following options:
1. Data pairs has diode bridge and spare pairs using single diode.
2. Data pairs has diode bridge and spare pairs has diode bridge.
3. Data pairs and spare pairs has has single series diode each, data pair should have diode bridge if the PD is auto-mdi-x.
Now lets consider the following case:
A multiport system activate port number x and send power to the PD.
The PD is configured per option 1 or 3.
Now, there is voltage present at the output of the oring diode, but, due to the fact that one of the leads of the spare pair is directly connected to one pair data pairs
There is a leakage current path from the data pairs to the spare pairs back to the PSE.
This leakage current will find its way to other ports in the PSE and may affect the detection function.
In some bob-smith termination configurations that was good for a switch without pse and are not suitable for switch with pse some ports may see voltages above 30V even if they are at OFF state.
In order to prevent such scenarios, option 2 is suggested that keep DC isolation from the spare pare to the data pairs and vice versa.
In addition, using diode bridge at the data pairs will fix the issue raised by Moti Goldish regarding the MDI-X/AUTO MDI-X issue.
Mandating diode bridge on both pairs will ensure powering of the PD in any PSE configuration and in any cable type straight or crossed cable
so we can eliminate the potential of interoperability problems regarding the ability to successfully powering the PD.
The data issue is solved by the definitions for the PSE and PD, by the pin assignment and polarity for the MDI/MDI-X/AUTO MDI-X configurations as described in tables 33-1and table 33-7.
Actually referring to Auto MDI-X in tables 33-1 and table 33-7 will not be required anymore.
The suggested remedy to support the above is:
Draft 4.2 page 60:
1. Delete the text at lines 50-51:
"If the interface is implemented as an MDI-X or Auto-MDI-X per Clause 14,the PD shall be polarity insensitive "
Replace it with the following text: "The interface in Mode A and in Mode B shall be polarity insensitive.
2. Consider to delete the reference for Auto-MDI-X from tables 33-1 and 33-7 as it is not required due to (1).
I believe that to mandate the above is required.
Please comment over the above issue as soon as possible.
PowerDsine Ltd. - Powering Converged Networks
1 Hanagar St., P.O. Box 7220
Neve Ne'eman Industrial Zone
Hod Hasharon 45421, Israel
Tel: +972-9-775-5100, Cell: +972-54-893019