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TCAN4550-Q1: Ratio between SPI speed and CAN speed

bar nahum
Prodigy 10 points
Part Number: TCAN4550-Q1

Tool/software:

Hello, I wanted to know if there is a defined ratio between the CAN-FD speed and the SPI speed.

For example, if I want to work at speed X in CAN, the SPI must be at speed Y or higher.

thank you very much.

  • 0
    TI__Mastermind 33030 points

    Hello, there is no dependency or ratio between the SPI and CAN-FD speeds.

    The CAN-FD bit timing is based on the clock frequency provided through the OSC1 and OSC2 pins.  The digital core of the device also uses the OSC1/2 clock which is usually either 20MHz or 40MHz.

    The SPI bit timing is based on the SCLK provided by the MCU with a max frequency of 18MHz.

    The device uses a FIFO on the SPI interface to handle the frequency domain boundary crossing between the SPI and OSC clock frequencies.  The data is input and output on the MCU based on the SCLK, and the digital core inputs and outputs data based on the OSC clock. 

    There is a dependency between the SPI clock and OSC clock frequencies with regards to this FIFO in that the SCLK must be at least 2MHz less than the OSC frequency.  For example if the OSC clock frequency is 20MHz, the maximum SCLK frequency is 18MHz.  Likewise, if the OSC clock was 10MHz, the SCLK must be 8MHz or less.  This is to ensure the digital core has enough clock cycles and time to load data into the FIFO during a SPI Read operation.

    But to your specific question, no, the CAN-FD bit timing is completely independent of the SPI timing.

    Regards,

    Jonathan