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Original question:

TCAN4550: Isolated CAN FD

TCAN4550: TCAN4550 -Test Mode to map RXD_INT_CAN and TXD_INT_CAN to GPIO1 and GPIO2

Roberto del Cano
Prodigy 10 points
Part Number: TCAN4550
Other Parts Discussed in Thread: ISO7731, ISOW1044

Tool/software:

Hi

We are looking at implementing CAN FD using a microprocessor that does not support it, hence we found some design reference notes suggesting the use of an external Controller like TCAN4550.

However we need the CAN FD to be isolated and TCAN4550 has an internal transceiver. It appears that there is a mode in TCAN4550 called 'Test Mode', section 8.4.4, in which GPIO1 and GPIO2 can be mapped with CAN Controller outputs:  RXD_INT_CAN and TXD_INT_CAN respectively. Then, I was thinking these can be connected to an external Isolator like ISO7731 and a TCAN1402 powered by an isolated converter.

What it is not clear to me is what a "Test mode" really means. Could you please expand on the implications on running normal communication operations while the TCAN4550 is configured in such way.

Also Could you please confirm suggested design approach to Isolate CAN FD? 

Many thanks in advance

Kind Regards

  • 0
    TI__Mastermind 33340 points

    Hi Roberto,

    The TCAN4550 integrates the MCAN (CAN FD) Controller and a CAN FD transceiver into a single package, and was the first device on the market to do this.  There are industry standard compliance test requirements for the CAN FD controllers, and also for the CAN FD transceivers which both require access to the RXD and TXD signals normally accessible in a two-chip solution.  Therefore, in order to perform these compliance tests, the internal RXD and TXD signals can be made accessible through the GPIO1 and GPO2 pins and is why this device configuration has been given the name "Test Mode."

    However, just because this configuration has the name "Test Mode" does not mean that it can't be used for normal applications such as yours with an isolated CAN transceiver. I'm not aware of any concerns or implications of using the TCAN4550 with an external isolated transceiver beyond some added loop delay (TX to RX) due to the fact it now has a longer propagation delay to the external transceiver.  This may limit the maximum bit rates your bus can support, but this would be a concern with any application, especially with isolation.

    So yes, I can confirm this is a valid design approach.  I would also suggest you consider using an Isolated CAN FD transceiver that combines the isolation with the transceiver for a more optimal solution.  TI has several options available you can review.  The ISOW1044 is one option to consider (Link).

    Regards,

    Jonathan