11.7.3 Key CAN FD/LIN Protection Design Points
• On the CAN DB9 connector shown in the figure above, the shield is not tied to the digital signal ground in CAN
as it is in other peripherals. The CAN definition states that CAN communication is a two-wire dif
ferential protocol
(CANH and CANL) bus. Dominant and recessive states of the bus are determined based upon the differential
voltage read between the CANH and CANL regardless of the ground.
• The shield must only be connected to the chassis/earth ground at only one point in the CAN network.
• On some CAN networks the optional power is also routed to the cable pin 9. In the event a user intends to
use that power source, beware that the line voltage fluctuations can be large. Also, the ground offset due to
large currents over the entire network would require an isolated AC/DC converter to isolate the MCU power and
ground from CAN cable power and ground.
• The 120 Ohm termination resistors can only be at both ends on the CAN network, therefore the switch to enable
or disable terminations depends on the user’s PCB order and location in the CAN network.
• A common mode choke is recommended for data rates over 1 mbps.
Note: It is a common belief that because a component vendor says their IC can withstand 15 Kv that it already
provides adequate protection on the I/O, but that is not the only requirement for external interface components and
signals. Usually the 15 Kv rating is for the IEC 61000-4-2 air discharge specification. This is fine for non-external
interface signals, but does not cover the IEC 61000-4-2 ESD contact discharge with an 8 Kv at 30 amp peak
current discharge requirement for equipment enclosure, external facing signals interfaces, ports, connectors, and
cable hardware.
Comprehensive information is available on ESD, EMI, and EFT on the Microchip web site that can be found in the
document: AN2587 - EMI, EMC, EFT, and ESD Circuit Design Consideration for 32-bit Microcontrollers, or on any of
the 32-bit product web pages under the tab Documentation > Application Notes.
Return to Checklist
Serial Data Corruption Errors
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Manual
DS70005439B-page 51
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