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© 2012 Semtech Corporation
www.semtech.com
PRELIMINARY
PROTECTION PRODUCTS
RClamp3374N
Applications Information
Gigabit Ethernet Protection Solutions
Ethernet systems with connections external to the
building are subject to high-level transient threats.
This type of equipment may even be required to meet
the surge immunity requirements of Telcordia GR-
1089. Reliable protection of the Ethernet transceiver
requires a device that can absorb the expected
transient energy, clamp the incoming surge to a safe
level, and yet remain transparent to the system under
normal operation. The
RClamp3374N has been
designed to meet these demanding requirements.
Transient Protection
When designing Ethernet protection, the entire system
must be considered. An Ethernet port includes
interface magnetics in the form of transformers and
common mode chokes. Transformers and chokes can
be discrete components, but integrated solutions that
include the RJ-45 connector, resistors, capacitors, and
protection are also available. In either case, the
transformer will provide a high level of common mode
isolation to external voltages, but no protection for
metallic (line-to-line) surges. During a metallic
transient event, current will flow into one line, through
the transformer and back to the source. As the
current flows, it charges the windings of the
transformer on the line side. Once the surge is
removed, the windings on the line side will stop
charging and will transfer its stored energy to the IC
side where the PHY IC is located. The magnitude and
Figure 1 - GbE Protection to Lightning, ESD, and CDE
duration of the surge is attenuated by the inductance
of the magnetics. The amount of attenuation will vary
by vendor and configuration of the magnetics. It is
this transferred energy that must be clamped by the
protection circuitry.
A typical protection scheme which utilizes the
RClamp3374N is shown in Figure 1. One device is
placed across two line pairs and is located on the PHY
side of the transformer as close to the magnetics as
possible. This is done to minimize parasitic inductance
and improve clamping performance. In this design, the
isolation voltage of the transformer is relied upon to
suppress common mode lightning surges. High voltage
capacitors and resistors are commonly utilized from
the center tap to ground to aid in transient protection.
Metallic surges will be transferred in some form to the
PHY side and clamped by the
RClamp3374N. The
RClamp3374N will turn on when the voltage across it
exceeds the punch-through voltage of the device. Low
voltage turn on is important since many PHY chips
have integrated ESD protection structures. These
structures are for protection of the device during
manufacture and are not designed to handle large
amounts of energy. Should they turn on before the
external protection, they can be damaged resulting in
failure of the PHY chip.
1
2
3
4
5
6
7
8
RJ-45
Connector
GbE
Ethernet
PHY
TP2+
TP2-
TP3+
TP3-
TP4+
TP4-
TP1+
TP1-
RClamp3374N
RClamp3374N
1
2
3
4
5
6
7
8
RJ-45
Connector
GbE
Ethernet
PHY
TP2+
TP2-
TP3+
TP3-
TP4+
TP4-
TP1+
TP1-
RClamp3374N
RClamp3374N
