8
Circuit Protection for High-Speed Serial Interfaces
Figure 2: Littelfuse circuit has a wide selection of protection solutions for power and communication ports (Source: Littelfuse)
Across the top of the chart are listed various ports based
on data speed, from the slowest on the left side to the
fastest on the right. Along the bottom, one will observe
two technology types—over-voltage solutions in blue
and overcurrent protection technologies in green. The
chart reveals which technologies to first consider when
looking for optimized port protection. Littelfuse can help
to further select parts based on the unique specifications
of a particular end-product design.
Ethernet
Protection for ethernet ports varies based on the level of
exposure to electrical hazards. For indoor applications
with minimal exposure to potential hazards, a single
ESD protector can be sufficient. A single diode array
placed after the transformer, such as the SRV05 Series
diode array can protect the Ethernet PHY in this case.
If one moves outdoors, the environment will be harsher,
increasing the risk of receiving damage because of
an electrical hazard. A fuse is needed to help protect
during a power-cross event when the power line makes
contact with the communication lines. Additionally, a Gas
Discharge Tube (GDT) such as the CG6 will help protect
against dangerous surge events associated with lightning
strikes. A diode array, such as the LC03, then adds
another level of protection, further clamping the surge
and protecting the PHY from damage.
RS-485
The protection of an RS-485 line varies by exposure
levels. For indoor or intra-building applications, a
polymeric positive temperature coefficient device (PPTC)
and diode-array combination will provide sufficient over-
current and over-voltage protection, however, if the port
connects outdoors, such as a rooftop unit, such as a
heating, ventilation, and air condition (HVAC) condenser
unit. A higher level of surge protection is needed and
provided by using a coordinated protection scheme
with GDTs and SIDACtors. A PPTC provides overcurrent
protection and acts as a coordinating element between
the GDT and the SIDACtors. The PPTC ensures that the
SIDACtor reacts first, providing fast protection until the
GDT can react.
CAN, LIN, SIM, µSIM
As automotive electronics, or the use of electronics in
automotive, have increased, so has CAN and LIN bus
prevalence. These communication lines require ESD
protection, typically provided by diode arrays. For these
automotive-related applications, it is important for all
electronic components to pass the rigorous standards of
AECQ and its included tests.
