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TCAN1463-Q1: CAN SIC Reduces Bus Ringing

Ryu Yamashita
Genius 3865 points
Part Number: TCAN1463-Q1


Tool/software:

Hi team,

I have a question regarding the section “How CAN SIC Reduces Bus Ringing” in the following document.

https://www.ti.com/lit/wp/slla581a/slla581a.pdf

My understanding is that if the timing of the reflected wave becomes extremely long, it may not be fully mitigated. Is this correct?
Additionally, if there are any examples or waveform examples showing significant improvement achieved by installing SIC in complex CAN wiring configurations, I would appreciate it if you could share them.

Best Regards,
Ryu.

  • +1
    TI__Guru 53396 points

    Hi Ryu,

    Yes, however, the suppression is dependent on many factors such as the network delay, stub length, prop delay, impedance mismatches, etc.

    Hence, the main difference is in how dominant to recessive is driven. With CAN FD, the driver impedance can go from low to very high leading to reflections I.e., say 50 ohms to 60 kohms. This mismatch causes reflections on the bus due to impedance mismatches, stubs, branches, connectors, harness capacitances, etc. However, with SIC, the driver do not immediately go to high impedance. Instead, it holds an active recessive drive with a moderate impedance of about 100 ohms for a defined tSIC_TX-base time, as shown in figure 3-2 of the document. Hence, allowing the bus settle, diminishing reflections before fully going passive.

    Figures 4-2 and 4-3 show waveform examples for a cleaner RXD which is received from the CAN driver / signal. See below for additional examples, thanks.

    Best Regards,

    Michael.