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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 ? The PSE could output 0V and be compliant. The PD must tolerate that voltage transient given minimum required PD supply capacitance. Regards, Pete From: Yair Darshan [mailto:YDarshan@xxxxxxxxxxxxx] Update: I was asked what problem I am trying to solve. See marked RED text. See below. Yair ----------------------- Hi all, 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. Proposed Remedy: 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 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: (1) “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:
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. Option 2 Any other simpler remedy or clarification? -------------------------------------------- Analysis: 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. -------------------------------------------- Darshan Yair Chief R&D Engineer Analog Mixed Signal Group Microsemi Corporation 1 Hanagar St., P.O. Box 7220 Cell: +972-54-4893019 E-mail: <mailto:ydarshan@xxxxxxxxxxxxx>. 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 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 |