So why does the CAN bus need extra protection? Doesn’t the transceiver provide adequate protection? CAN was originally developed for data communications in the automotive industry, which is a noisy, harsh environment. CAN nodes are subject to high energy transients such as load dump, inductive load switching, relay noise, and ignition switching noise. The most popular physical layer in CAN is specified by ISO-11898. ISO-11898 compatible transceivers do a good job of filtering out noise coupled on the bus and protecting the node from energy spikes and short circuit conditions. For example, the MCP2515 can withstand shorts of ±42V on the bus and can withstand transient energy spikes of ±250V without damage to the node. Additionally, the differential signaling on the bus helps filter out noise. However, in some systems, the environment is harsh enough that extra protection and/or extra filtering is needed to protect the node and ensure clean communications.