[SI-LIST] Re: RJ-45 Connector
- From: "Curt McNamara" <CurtM@xxxxxxxxxxx>
- To: "Joel Brown" <joel@xxxxxxxxxx>, <leeritchey@xxxxxxxxxxxxx>
- Date: Fri, 9 Jun 2006 12:25:08 -0500
IF safety approvals are not a concern (i.e. this is not a CE marked
product or is exempted from the standards) then this is fine advice, and
will keep you away from ESD issues as well.
I have designed and gotten CE approval for products (ISDN) where this
coupling on the output side was critical. There are also Ethernet
devices that need to pass Class B for the US where the common mode
coupling can be an issue as well. It all depends on your system.
Curt
Curt McNamara. P.E.
Senior Electrical Engineer
Logic Product Development
411 Washington Ave. N Suite 101
Minneapolis, MN 55401
Tel 612-436-5178
Fax 612-672-0443
curtm@xxxxxxxxxxx
www.logicpd.com
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-----Original Message-----
From: Joel Brown [mailto:joel@xxxxxxxxxx]
Sent: Friday, June 09, 2006 11:45 AM
To: leeritchey@xxxxxxxxxxxxx
Cc: Curt McNamara; Chandupcb; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: RJ-45 Connector
My understanding from a question I previously posted was that
the board ground should not go past the Ethernet magnetics for fear that
common mode noise would couple from the board ground to the RJ45 side of
the magnetics and radiate out on the Ethernet cable.
It was suggested that the area under the RJ45 should be
connected to chassis ground with a split between chassis ground and
board ground. This was recommended in an Intel app note, but our EMI
consultant said it was wrong and recommended we run the board ground
under the RJ45 with no plane split and also to connect the RJ45 shield
to chassis ground.
Joel
Lee Ritchey wrote:
Curt,
The creepage distance is on the surface, not
internally. The internal
spec is 1700 VDC withstanding and that is achieved with
only 2 mils of
FR-4. So, there is no need to clear planes that are
internal to the PCB.
Why do engineers globally apply specs, when they don't
apply?
Yes, there is one regulator person in Australia who does
not understand
this and insists that planes need to be cleared. He is
out to lunch! We
solved the problem by just not shipping to Australia!
The whole market in
Australia is less than half of Californina, so it wasn't
much of a
sacrifice.
[Original Message]
From: Curt McNamara <CurtM@xxxxxxxxxxx>
<mailto:CurtM@xxxxxxxxxxx>
To: <leeritchey@xxxxxxxxxxxxx>
<mailto:leeritchey@xxxxxxxxxxxxx> ; Chandupcb <chandupcb@xxxxxxxxx>
<mailto:chandupcb@xxxxxxxxx> ;
<si-list@xxxxxxxxxxxxx> <mailto:si-list@xxxxxxxxxxxxx>
Date: 6/9/2006 9:10:42 AM
Subject: [SI-LIST] Re: RJ-45 Connector
From a safety standpoint the "line side" of the
RJ45 can be TNV
(tele-communications network voltages). These
wires can go through
wiring cabinets where a single fault could short
them to AC (Ethernet),
or could go on poles outside the building (DSL
or modem). As a result
approval bodies require a transformer for
isolation between TNV and
SELV. To ensure the isolation, you need to keep
minimum distances
(called creepage and clearance) between these
line side signals and
anything on the SELV (safety extra low voltage)
side. In practice this
requires there be no planes under the output
side, since the distance
between the planes and the output traces or pins
would violate the
standard. You should check with your approvals
body to ensure that the
correct standard is being applied.
Curt
Curt McNamara. P.E.=20
Senior Electrical Engineer=20
Logic Product Development=20
411 Washington Ave. N Suite 101=20
Minneapolis, MN 55401=20
Tel 612-436-5178=20
Fax 612-672-0443=20
curtm@xxxxxxxxxxx=20
www.logicpd.com=20
This message (including any attachments)
contains confidential
information intended for a specific individual
and purpose, and is
protected by law. If you are not the intended
recipient, you should
delete this message and are hereby notified that
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copying, or distribution of this message, or the
taking of any action
based on it, is strictly prohibited.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Lee Ritchey
Sent: Friday, June 09, 2006 11:00 AM
To: Chandupcb; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: RJ-45 Connector
Chandu,
There is no valid reason to do this. Rules like
this are often called
elephant repellant.
[Original Message]
From: Chandupcb <chandupcb@xxxxxxxxx>
<mailto:chandupcb@xxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
<mailto:si-list@xxxxxxxxxxxxx>
Date: 6/9/2006 3:46:00 AM
Subject: [SI-LIST] RJ-45 Connector
Hi Gurus,
May I know why will we remove the Plane
under the RJ-45=20
connector.Some
times only chasis gnd is Allowed under the
connector.
Why?
Regards
Chandu
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