Physical Layer - CAN System Engineering - page 89

2.4.2.3 Bus Filter

Besides the applied transceiver, the implementation of the bus filter has great influ-
ence on the EMC characteristics of the systems as a whole. According to the EMC
requirements of the application, there is a different emphasis on the implementations:

• Industrial control: High priority on protection against burst pulse, surge pulse
and ESD.
• Automotive: Focus mostly on protection against HF interference and ESD.

2.4.2.4 Transceiver

CAN transceivers represent the physical interface between the CAN bus system and
the bus lines. Therefore, the transceiver itself has great impact on the EMC charac-
teristics of the system as a whole. Especially for in-vehicle applications, the trans-
ceivers must meet increased requirements, as in this application only UTP bus lines
are applied. Therefore, higher level noise amplitudes may get to the transceiver.
The most important requirements for CAN transceivers are as follows:

• Immunity against common-mode interference with high amplitudes due to the
induction of interference fields and transients into the bus lines.
• Immunity against differential-mode interference with relatively low amplitudes,
coming from the induction of noise into the non-symmetrical bus lines (or bus
segments) or induced by the common-mode-differential-mode conversion
caused by non-symmetries in the filter electronics or the transceiver by itself.
• Immunity against common-mode and differential-mode noise in conjunction
with ground offset between different bus nodes.
• Sufficient protection against damage caused by ESD.
• High degree of symmetry of the bus signals in order to avoid emission of com-
mon-mode noise through the bus lines.

These most important requirements led to the development of an EMC test specifi-
cation for CAN transceivers. These requirements are mostly relevant for car elec-
tronics and they partially represent the constraints for EMC qualification. The test
specification is described in more detail subsequently.

2.4.3 EMC Evaluation of CAN Transceivers

2.4.3.1 Ways for EMC Evaluation for Cars Applications

For the evaluation of the EMC characteristics of semiconductors in car applica-
tions, there are analysis methods available covering all phases of the development
process. Table 2.1 depicts the environmental conditions and the range of dynamics
for all three test levels.