TCAN4550: When using External CAN Transceiver

Hello AP,

Thank you for your patience while I was out of office last week.

AP said:

It seems that WUP pattern detection and t_WK_FILTER are located/used in/by the integrated CAN FD transceiver block? How does WUP work when an external transceiver is used? Does any activity on RXD_INT acts like a WUP pattern (and no filter applies)?

The external transceiver would need to be able to detect a WUP and then wake up the system.  When using the internal transceiver, the MCAN Controller is disabled and in Sleep Mode, and there is an internal low power detection circuit that remains active to detect a WUP condition.  When using an external transceiver, the TCAN4550 will not be able to detect a WUP.

AP said:

It seems that three features are filed under Failsafe but only the third feature mentioned (with CANSLNT flag) is controlled via the FAILSAFE_EN bit?
Does this third feature apply when using an external transceiver?
Meaning: What is monitored here: bus activity by the internal transceiver block (which is disabled I guess when an external transceiver is used?) or RXD_INT activity by the CAN core?

This CAN Silent failsafe feature is just a monitoring circuit that has a timer that is reset every time there is a transition detected between the dominant and recessive states.  This is not done inside the MCAN controller core but as part of the internal transceiver.  When using an external transceiver, I don't believe this failsafe feature is valid and you would need to rely upon any failsafe features of the external transceiver if you still wanted to CAN Silent detection.

AP said:

The TXD Dominant Timeout feature doesn not apply when using an external transceiver repectively depends on the features of the external transceiver?

Yes again, this is a feature of the actual CAN transceiver and not done within the MCAN core.  Most transceivers include a Dominant Timeout failsafe feature, so you would need to rely upon that feature in the external transceiver you are using.

AP said:

Are the Thermal Shutdown and INH Pin device features available & functional when an external CAN transceiver is used? Just asking because these seem to be shown in the CAN Transceiver Block Diagram (which may be internally disabled when using an external CAN transceiver).

Yes, the thermal shutdown is monitoring the internal die temperature of the device.  If there is a short circuit type of event that results in a large power dissipation that heats the device, then the device should shut itself down.

The INH pin will be driven High when the device is in either Standby or Normal modes regardless of whether the internal transceiver or an external transceiver is used.

Regards,

Jonathan