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ISOW1044: Inquire about CAN communication availability

JH Shin
Mastermind 8455 points
Part Number: ISOW1044
Other Parts Discussed in Thread: SN74HCS09, SN74HCS157-Q1, TMUX1112, , ISO1044

Hello,

My customer wants to connect CAN communication using ISOW1014, SN74HCS157-Q1, and SN74HCS09 as shown below to implement a special function.

Q1. If multiple CANn_RxD signals are never received simultaneously, is it possible to receive CAN signals from MCU_1?

Q2. Is normal CAN communication possible with MCU&AP through SN74HCS157-Q1?

Q3. Is there a problem with CAN communication when connecting a 120ohm termination resistor using TMUX1112 as shown below?

Thank you.

JH

  • 0
    TI__Guru 53685 points

    Hi JH,

    Thank you for reaching out and sharing necessary information related to your questions. Please find my inputs to the questions you have listed out.

    A1. Yes, this should be fine for MCU_1 to receive CAN data from the bus when the MUX switch SN74HCS157-Q1 is connected to MCU_1. Please note that the propagation delay of SN74HCS157-Q1 and SN74HCS09 should be taken into account to support CAN datarate.

    A2. Yes, this should be fine for MCU&AP to receive CAN data from the bus when the MUX switch SN74HCS157-Q1 is connected to MCU&AP. Please note that the propagation delay of SN74HCS157-Q1 should be taken into account to support CAN datarate.

    A3. This should work fine when the common-mode voltage on the CAN bus is 0V but a CAN bus needs to support -2V to +7V (more commonly ±12V) of common-mode voltage to work fine when connected to CAN network in real-world. To get an answer to this question, I would request you to post this question on Switches & Multiplexers E2E forum. I am posting the link to Switches & Multiplexers E2E forum.

    https://e2e.ti.com/support/switches-multiplexers-group/switches-multiplexers/f/switches-multiplexers-forum

    Let me know if you have any other questions, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Mastermind 8455 points

    Hi Rao,

    Thanks for your reply.

    The customer has additional questions.

    Q1. They want to use CAN communication speed of 5Mbps. The total propagation delay of SN74HCS157-Q1 and SN74HCS09 is significantly shorter than 5Mbps (200nS). Accordingly, can we assume that there is no problem with 5Mbps support?

    Q2. They want to receive the CAN wake-up pattern from MCU1 through SN74HCS157-Q1 and SN74HCS09 during standby and then control SN74HCS157-Q1 with MCU1 so that MCU&AP perform CAN communication. Please let us know if there are any problems with this scenario.

    Thanks,

    JH

  • 0 in reply to JH Shin
    TI__Guru 53685 points

    Hi JH,

    Thank you for the follow-up questions, please see my inputs below.

    A1. The required propagation delay is something that customer would have to estimate for their system and accordingly choose. The propagation delay by the MCU to process data will also need to be accommodated to estimate loop delay.

    A2. ISOW1044 doesn't support CAN wake-up feature. If this is what they are looking for then ISOW1044 won't be able to support it. If customer is referring to passing signals from MCU to ISOW1044 through SN74HCS157-Q1 and SN74HCS09 then this shouldn't be an issue. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Mastermind 8455 points

    Hi Rao,

    Thanks for the prompt reply.

    For Q2, I can find the remote wakeup via BUS WUP in the data sheet as shown below.

    Could you please recheck the customer's inquiry?

    Thanks,

    JH

  • 0 in reply to JH Shin
    TI__Guru 53685 points

    Hi JH,

    Thank you for re-checking on the CAN BUS WUP feature.

    Apologies for the confusion, I confused ISOW1044 to ISO1044 where ISO1044 doesn't support WUP feature while ISOW1044 does. I would like to correct myself and re-clarify that ISOW1044 support remote wakeup via BUS wake-up pattern according to ISO 11898-2:2016.

    I would also like to answer your earlier question that the CAN wake-up pattern will be received into MCU1 through SN74HCS157-Q1 and SN74HCS09 during ISOW1044 standby and then it would be fine to control SN74HCS157-Q1 with MCU1 so that MCU&AP can perform further CAN communication.

    Let me know if anything is not clear, thanks.


    Regards,
    Koteshwar Rao