Ringing suppression in CAN FD networks

CAN in Automation (CiA) has released the CiA 601-4 draft standard proposal specifying the ringing suppression in CAN FD networks.

The basic idea is simple: The specified circuitry changes the overall impedance for a short time after the dominant-to-recessive state change. The duration depends on the chosen data-phase bit-rate.

In CAN FD networks using singe-star or multiple stars or hybrid (star plus linear bus) technologies, the ringing on the bus-lines limits the maximal possible data-phase bit-rate. Therefore, the ringing suppression is very important.

Most of the carmakers will migrate to CAN FD networks within the next few years. CAN FD standardized internationally in ISO 11898-1:2015 supports higher bit-rates in a part of the data frame. Additionally, the improved data link layer protocol features payloads of up to 64 byte. The Classical CAN protocol was limited to an 8-byte data field.

The CiA 601-4 document is released CiA internally, but interested parties may request a personalized copy from CiA headquarters in Germany. The ringing suppression circuitry specified in this document can be implemented in ISO 11898-2 compliant transceivers or implemented as a stand-alone circuitry.