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TCAN4550-Q1: Data rates and clock frequencies

Gregory Grzesiak1
Prodigy 10 points
Part Number: TCAN4550-Q1
Other Parts Discussed in Thread: TCAN4550,

Hi All

I noticed that for

TCAN4550 at 40MHz OSC and 18MHz SPI CLK the data rate is 5Mbps whereas for 

TCAN4550-Q1 at 40MHz OSC and 18MHz SPI CLK the data rate is 8Mbps,

From where this difference comes from?

there is a topic on this forum that states OSC tollerance of 0.5% for data rates bellow 1Mbps and 0.15% for 1-5Mbps,

What tolerance should 40Mhz crystal have to get 8Mbps?, does the tolerance requirement change when 20MHz crystal is used? 

Does SPI clock tolerance has influence on the maximum data rate?

Thank you 

Best

  • 0
    TI__Intellectual 2090 points

    Hi Gregory,

    Thank you for your questions.  

    SPI clock tolerance can have an effect on maximum data rate, although at 20 MHz and 40 MHz frequencies, the tolerance effect should be minor compared to the effects of CAN bus architecture design decisions.  As you have referenced, it is better that 0.15% clock tolerance be followed for CAN FD speeds greater than 1 Mbps.  

    Higher clock frequency (40 MHz) and higher clock accuracy is recommended for 8 Mbps data rates, since the bit time drops to 125ns, which limits the number of clocks per bit (time quanta).  This is 

    As far as the difference between TCAN4550 and TCAN4550-Q1, some automotive customers have become interested in 8Mbps data rates.  However, the automotive CAN FD industry standard (ISO11898-2:2016) does not specify timing performance for CAN data rates above 5 Mbps.  Each customer must decide performance limits for their own CAN bus applications.  This includes multiple considerations, including bus architecture, number of nodes, power isolation, etc.  Given the market interest, though, we have specified timing limits for the TCAN4550-Q1 at the transceiver level for 8 Mbps operation.

    Let me know if I can clarify anything further.

    Best Regards,

    Max Megee

    TI Transceiver Applications