CAN is a 2-wire differential communications interface which has its physical layer defined by the ISO 11898-2 standard. The physical layer consists of the CAN transceiver and the twisted pair cabling that connects all the CAN nodes together. The two lines connecting the CAN transceiver to the cabling are referred to as CANH and CANL. It is also recommended to terminate the CANH and CANL lines with a split termination to avoid signal reflections and high frequency noise. Figure 1-1 illustrates the typical CAN bus setup.

The CAN protocol can come in many different flavors and speeds. These flavors include:

• Low speed (LS CAN): Up to 125 kbps
• High speed (HS CAN): Up to 1 Mbps
• Flexible data rate (CAN FD): Up to 5 Mbps
• Signal Improved capable CAN (CAN SIC): Up to 8 Mbps
• CAN XL: Up to 10-20 Mbps (not yet released)

ESD can happen to any system with exposed connectors, including CAN bus interfaces. Typically, these connectors are exposed during vehicle assembly and maintenance. For example, when a car is going through assembly, the cabling needed to connect the control modules in the car can accumulate an excess amount of charge on them as they move through the factory. When it comes time to connect these cables to the control modules that hold the CAN transceivers, the excess charge will flow from the cable to the module and into the CAN transceiver. Depending on the environmental conditions in the factory and how the cabling is handled, these discharges can get up to 30 kV and permanently damage the CAN transceivers, making the vehicle inoperable. This can also happen if a mechanic is performing maintenance on a car and has to disconnect and reconnect this cabling. In short, any time the cabling is manipulated in the system, there is a chance for ESD to occur.