EMC 40 (114)
4 EMC
This section offers information, necessary when designing in an Anybus CompactCom, to
ensure sufficient performance related to EMC. However, an engineering assessment is always
needed to ensure the quality. HMS Industrial Networks AB does not leave any guarantees, but
provides relevant information to the customers.
4.1 General
When working with a design in relation to EMC, it is recommended to always aim for good
signal integrity, since this is highly related to the EMC. For power, this means solid planes for
both power and GND together with good decoupling between the planes. As the quality of the
power is of great importance, it is important to perform sufficient verifications during the design
process to ensure this. This is also true for signals, where good signal integrity most likely
results in good EMC performance. There should always exist good connection to a reference
plan without any obstacles for the return current. Traces should also be kept short, with as few
board and cable transitions as possible, since every transition will have a negative impact on
the signal integrity.
Also, different protocols are more sensitive to interference than others. E.g. try to avoid using
parallel and RMII interface in the design, if the recommendations in this section cannot be
followed or if the risk of interference is high. To ensure stability, there has to be a sufficient
separation on the host board between a parallel interface and an RMII interface.
4.2 Header Footprint
Guidelines regarding the compact flash header footprint is presented in Without Housing, p. 99.
This layout is designed to ensure stable connection between the Anybus CompactCom board
and the main board for both power, GND and signals (pin list can be found in Power Supply
Pins, p. 12).
4.3 Bulk and Decoupling
Recommendations regarding bulk and decoupling capacitors is presented in Bypass
Capacitance, p. 50.
The capacitors have impact on the power quality at the Anybus CompactCom board, but are
also of importance in relation to EMC immunity. These general recommendations should be
evaluated for every design. The values may also need to be adjusted in relation to power
consumption, power quality on the main board, and the layout of the main board.
4.4 Reset Signal
There are several aspects to consider when routing the reset signal for the Anybus
CompactCom. Requirements for rise and fall time, but also the relation between the power up
and the reset signal are described in RESET (Reset Input), p. 18. These requirements must be
met in all designs to ensure stability. If the reset signal has a long trace or if there is any other
aspect that has a negative impact on the signal integrity, an RC filter may be required. To
minimize the risk of EMC problems, it is possible to add footprints for a RC-filter in advance and
evaluate the need before it becomes a problem during any certification. When designing the
filter, all timing aspects must be considered, so that the timing requirements in RESET (Reset
Input), p. 18 are fulfilled.
Anybus
®
CompactCom
™
M40 Hardware Design Guide HMSI-216-126 EN 2.6
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