Yair:
Going back to clause 33, I would ask isn’t the very point of this language to indicate that there is
no output voltage requirement on the PSE during a transient condition less than 30 usec ?
Yair; The text in clause 33 may indicate that the PSE has no requirement at below 30usec however it is just
“indicate”
and I am looking for clear requirement. I am OK that the text in 802.3bt will say that below 30usec PSE may turn OFF etc. i.e. I am looking for clear instruction and not leave it to the implementer to guess what the spec says.
The PSE could output 0V and be compliant. The PD must tolerate that voltage transient given minimum required PD supply capacitance.
Yair: If I do the calculations, not always PD can keep the voltage for transients <30usec with the minimum PD input capacitor.
Bottom line: PSE can do many thisgs. We need just to say what it is. As I read the spec in the PSE section now, I see that everything is defined above 30usec but
in <30usec range the spec just says that the voltage can go below Vtran-2P but it doesn’t say what to do with this info.
Regards,
Pete
Peter Johnson
Sifos Technologies
1 Tech Drive
Andover, MA 01810
www.sifos.com
Update: I was asked what problem I am trying to solve. See marked RED text.
I am considering the following comment (page 176 line 24):
“Transients less than 30 μs in duration may cause the voltage at the PI to fall below VTran-2P.
See 145.3.8.6 for PD transient requirements”
For transients <=30usec,
the PSE has no mandatory requirements or other i.e. what are the requirements from the PSE for a transient below 30usec. The PD requirements for transients
below 30usec are clear. The PD must continue to operate down to 34V.
See below analysis after the proposed remedy section.
Option 1 (Vtran-2P from 0 to 250usec):
Make the following changes:
“A PSE shall maintain an output voltage no less than VTran-2P
for transient conditions lasting
more than 30 μs and less than 250 μs, and meet the requirements of 145.2.10.9.
Transients less than 30 μs in duration may cause the voltage at the PI to fall below VTran-2P.
See 145.3.8.6 for PD transient requirements.
Option 2 (Different values for Vtran-2P @ <30usec and from 30usec to 250usec):
Make the following changes:
“A PSE shall maintain an output voltage no less than VTran-2P
for transient conditions lasting more than 30 μs and less than 250 μs, and meet the requirements of 145.2.10.9.
Transients less than 30 μs in duration may cause the voltage at the PI to fall below VTran-2P.
See 145.3.8.6 for PD transient requirements.
A PSE shall maintain an output voltage no less than VTran-2P_low
for transient conditions lasting less
than 30 μs and meet the requirements of 145.2.10.9.
(2) Change Item 3 in Table 145-16 as follows:
|
Item
|
Parameter
|
Symbol
|
Unit
|
Min
|
Max
|
PSE Type
|
Additional Information
|
|
|
Output voltage during transient
|
VTran-2P
|
Vpp
|
45.3
|
-
|
3
|
|
|
48.4
|
-
|
4
|
|
VTran-2P_low
|
43.31
|
-
|
3
|
|
46.41
|
-
|
4
|
Note 1: These value is quick estimation. If the group agrees to the remedy, I will RUN a simulation to find the exact PSE voltage at these conditions (34V at the
PD for <30usec). This note will be remove after finalizing the remedy.
Any other simpler remedy or clarification?
--------------------------------------------
145.2.10.3 Voltage transients
A PSE shall maintain an output voltage no less than VTran-2P
for transient conditions lasting more than 30 μs and less than 250 μs, and meet the requirements of 145.2.10.9.
Transients less than 30 μs in duration may cause the voltage at the PI to fall below VTran-2P.
See 145.3.8.6 for PD transient requirements.
[Yair: the missing info is what is the requirements for PSE for transients less than 30usec]
Transients lasting more than 250 μs shall meet the VPort_PSE-2P
specification.
145.3.8.6 PD behavior during transients at the PSE PI
A PD shall continue to operate without interruption in the presence of transients:
— lasting longer than 30 μs and less than 250 μs at the PSE PI as defined in 145.2.10.3, and causing
the voltage at the PD PI to fall to no less than VTran_PD-2P, as defined in Table 145–29;
— lasting less than 30 μs and causing the voltage at the PD PI to
fall to not less than 34 V.
[Yair: here the spec is clear. The PD must continue to operate down to 34V with transients <30usec.
If the voltage drops to 34V, it is 2V less than the 36V transient limit in Table 145-29. This may result with increased voltage drop on the PSE PI by at least 2V.]
During a transient the input power of the PD may exceed PPeak_PD
or PPeak_PD-2P. Table 145–30 defines three
PSE output voltage transients.
--------------------------------------------
Analog Mixed Signal Group
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
To unsubscribe from the STDS-802-3-4PPOE list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-4PPOE&A=1