TCAN1044A-Q1: different between CAN transceiver and CAN Controller

Hi Kai,

Great question!

A CAN transceiver such as TCAN1044A deals with converting a digital signal to/from a differential CAN bus signal. Such a device is responsible for meeting all of the electrical characteristics defined by the ISO 11898-2 CAN specification. This ensures that all connected CAN transceivers agree on what voltage levels are interpreted as recessive or dominant state (logic 1 and 0 respectively). Apart from some edge cases, the transceiver does not care about the actual data being sent through it. When TXD is 0, it drives the CAN bus dominant. When the CAN bus is dominant, it drives RXD low. etc.

A CAN controller on the other hand deals with the protocol requirements of the ISO 11898-1 CAN standard. This includes formatting the CAN frame into the its defined structure including arbitration fields, control fields, data fields, CRC, etc. Every time a processor needs to send a CAN frame, it depends on the CAN controller to format the information properly so that it may be transmitted on the CAN bus. The output for the CAN controller (in most cases) is the TXD and RXD digital signals. These will be connected to a CAN transceiver so that the signal may be converted into the proper electrical domain for the CAN bus. 

TCAN4550 serves both of these functions as it has a CAN controller and CAN transceiver integrated. It is capable of taking data from a SPI connection and converting both the protocol information and electrical parameters to a CAN bus. This is very handy when the MCU in a design does not have a CAN FD controller integrated. 

An interesting case device would be something like TCAN1145. This transceiver still needs a CAN controller to properly interface with a CAN bus during normal operation, but the partial networking feature gives this device a bit more smarts than your average transceiver. While in Sleep mode, the CAN controller is most often turned off so there's nothing capable of interpreting the CAN data. The partial networking feature of TCAN1145 allows the transceiver to recognize CAN data and wake the local node when it sees a CAN ID that matches its configuration. However, once the node wakes up fully, it is the CAN controllers duty to send data back and forth on the CAN bus. 

I hope this clears some things up regarding the differences here. Let me know if there's anything else I can elaborate on and if you have any more questions.

Regards,
Eric Schott