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TCAN4550-Q1: TCAN4550-Q1

Part Number: TCAN4550-Q1
Other Parts Discussed in Thread: TCAN4550

Dear Max Megee

I heard ceramic resonator of frequency accuracy is 0.3% can use a clock of IC with CAN-FD when operating at CAN-FD speeds from customer and standards organization.

If oscillator accuracy for CAN-FD is 0.15% when PLL uses,  Is PLL frequency accuracy of 0.35%?

I think 0.15% is too tight.

Please tell me the reason that  IC need  oscillator accuracy 0.15% when CAN-FD use.

Could you share datasheet of TCAN4550?

Ishimasa

  • Hello Ishimasa-san,

    You should be able to request the full datasheet here:

    www.ti.com/.../TCAN4550-Q1

    (Access requires our approval since this part is still in pre-release status. We should approve within one day, though.)

    Since this part is not yet released, we are still working through some updates to the datasheet. I'm not sure the current version specifies the clock accuracy. However, the accuracy concerns for this device would be the same as for most other CAN controller implementations, and you can see the how clock accuracy impacts the integrity of the sampled data stream in this paper:

    www.can-cia.org/.../2013_mutter.pdf

    This shows that an accuracy of 0.5% is acceptable for FD data phase rates up to 5 Mbps. This is true of the TCAN4550 as well.

    However, when operating at these higher rates over a realistic network, other factors can start to degrade the timing margin (such as bit timing distortion due to clock jitter, delayed edges due to capacitive loading, glitches occurring due to bus ringing, etc.). For this reason many users opt to improve the oscillator accuracy to 0.15% in order to provide better timing margin. Again, these concerns would apply to CAN FD in general and are not exclusive to TCAN4550.

    Does this all make sense? If I can provide any further information please let me know.

    Regards,
    Max Robertson
  • Dear Max Robertson

    Thank you for your quick response.

    Thank you for your quick response.

    I couldn't find 0.15% of clock tolerance in blelow datasheet.

    www.ti.com/.../TCAN4550-Q1

    Could you share detail datasheet taht show external clock needs 0.15% to use CAN-FD ?

    Below report shows that Frequency tolerance is an Accumulating Errors.

    www.can-cia.org/.../2013_mutter.pdf

    CAN Transceiver (ringing) and PLL jitter are non-accumulating Errors.

    Do CAN Transceiver and PLL jitter inflence clock tolerance?

    Best regards

    Ishimasa

  • Ishimasa-san,

    Our current datasheet does not specify clock tolerance. The TCAN4550 will not skew the clock tolerance, though, and so 0.5% is still an acceptable value to achieve working CAN FD communication. Using more accurate clocks can allow more timing margin on the CAN FD bus, though, and this can be helpful if there are other factors impairing communication outside just clock tolerance. Because of this, some users of CAN FD require 0.15%. However, this would be a system-level requirement, not a requirement of TCAN4550. TCAN4550 can function at CAN FD rates with a 0.5% clock.

    Please let me know if this is unclear.

    Regards,
    Max