SLLA581 April   2022 TCAN1462-Q1 , TCAN1463-Q1

 

  1.   Trademarks
  2. 1What is SIC?
  3. 2The Limitations of Classical CAN and Regular CAN-FD
  4. 3How CAN SIC Reduces Bus Ringing
  5. 4Experimental Results on TI’s TCAN1462 Device
  6. 5TI’s CAN SIC Devices
  7. 6Benefits of CAN SIC

2 The Limitations of Classical CAN and Regular CAN-FD

The first-generation CAN protocol, ISO 11898-2, also known as Classical CAN, was released around 1993. The protocol allowed only 8 bytes of payload data transfer, and a maximum specified data rate of 1 Mbps. These limitations were quickly realized in automotive applications, where vehicles have a number of electronic nodes that communicate with each other using the CAN bus.

The CAN-FD protocol specification was released around 2015, which increased the payload length to 64 bytes and the maximum signaling rate in the data phase to 5 Mbps. The arbitration phase signaling rate was still limited to 1 Mbps, however, for backwards compatibility with Classical CAN.

While CAN-FD brought the advantages of a faster data rate and a longer payload, it wasn’t sufficient to keep pace with the ever-increasing number of ECUs added to vehicle CAN bus networks. Designers realized that they could not harness the real potential of CAN-FD transceivers, as bus ringing resulting from complex star networks affected correct signal communication. Figure 2-1 is an example star topology.

Figure 2-1 CAN Nodes Connected in a Star Network

In complex star topologies with multiple stubs, a signal traveling on the bus experiences impedance mismatch which causes reflections. These reflections distort the CAN bus and cause it to oscillate, resulting in an incorrect CAN bus level and RXD at the sampling point. Although these network effects were not specific to CAN-FD networks, at the lower-speed operation of Classical CAN the bit duration was longer, and the bus ringing diminished such that it was possible to sample the correct bit, as shown in Figure 2-2, resulting in correct communication.

Figure 2-2 CAN Bus Ringing and RXD Glitch for Classical CAN Speeds

For 5-Mbps CAN-FD operation, a 200-ns bit duration was much too small for the ringing in complex star topologies to disappear, hampering reliable data communication. This deterred system designers from using CAN-FD at 5 Mbps.

With an increase in the exchange of network data and faster throughput demands in modern-day vehicles, CAN SIC paves the way for a next-generation in-vehicle communication bus technology that is faster and provides more network flexibility and scalability.