Jo:
First, let me thank you for your work on
these items.
As I recall, the discussion that resulted
in 420 mA centered on the group’s understanding of the cable derating
requirements. If my recollection is correct, the cable derating would
allow for up to 420 mA per conductor. This per conductor rating of 420 mA
does indeed mean that the pair would carry 840 mA.
The Study Group felt comfortable defining
the characteristics of our devices but felt we should leave issues that are a
result of cabling characteristics to the cabling experts. You would need
to incorporate the cable systems attributes that you feel are necessary to our
device model in order to complete the total system model.
I am not a PHY expect nor even PHY competent,
I will see that the issue of momentary disconnect under load is brought to the
attention of those who are PHY knowledgeable.
Cheers
Mike
Michael McCormack
Texas
Instruments, Power Interface Products
50 Phillippe Cote St.
Manchester, NH 03101 USA
Voice: +1 603 222 8686
Fax: +1 603 222 8580
Email: mike_mccormack@xxxxxx
Web Site: http://www.ti.com
From: Jo Walling [mailto:jo.walling@xxxxxxxxxxxx]
Sent: Tuesday, October 04, 2005
8:56 AM
To: McCormack, Michael
Subject: PoEP
Importance: High
Hi Mike,
I am just back from Edinburgh's
ISO/IEC meeting. We discussed there also your letter. There are
some points to clarify:
1.) You mentioned that you would like to transmit 420 mA over EACH
conductor. Your sketch shows, however, transmission over the common mode
circuit of two pairs, i.e. over two parallel condcutors. Then you mention
that the circuit components were laid out for 420 mA.
2.) If 420 mA are on each conductor, then the circuit has to be laid out for
840 mA over the common mode circuit.
3.) The circuit does not yet reflect the capacitance and inductance of the
cabling. I guess this will have to be added by IEC 48B (Connector group)
Please clarify these points.
I have another question: The blades on the RJ-45 plugs are crimped onto
the condcutors. As a result they are all not exactly on the same level.
The leads in the connector have also some inherent irregularities. That
means if the plug is pulled out of the connector, one of the condcutors of the
common mode circuit is opened first, pulling to all likelihood an arc.
However the other conductor is not yet open. As a result the transformer
with the center tap is only on one side loaded. This will create an
induction in the other side, and may affect your chips. Did you guys
consider this?
In Edinburgh we
intended first to get back to the now Task Group with a statement about the
maximum ambient operating conditions, which have to be substantially
reduced. However the chair of SC25 requested that the component groups in
IEC are involved first, prior to working out any recommendation. You will
hear about it more and more detailed either from Alan Flatman or Massod Sharif.
Kind regards,
Jo Walling
Dr.-Ing. J.-
H.(Jo) Walling
Consultant
, 431
Church
Beaconsfield,
QC
H9W 3R9, Canada
( Phone: (514) 695-8220 or (514)
695-6063
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* Email : jo.walling@xxxxxxxxxxxx