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AM5718: DCANRX tW period

Tony Tang
Mastermind 25276 points
Part Number: AM5718
Other Parts Discussed in Thread: SN65HVD251

AM5718 DCANRX period is H-15 to H+15 ns, is this required by AM5718, or required by CAN protocol?

I checked it on AM335x, AM437x datasheet, it is H-2 to H+2 ns. seems this parameter specific to devices.

Now, my customer use SN65HVD251 with AM5718, test result as below, the RX timing can't meet AM5718 requirement.

My question, can this device work with AM5718?

Check with SN65HVD251 FAE, the timing output from SN65HVD251 can't be ajusted.

  • 0
    TI__Guru**** 393215 points
    The factory team have been notified. They will respond here.
  • 0
    TI__Expert 4005 points

    Tony, 

    The AM5718 is a general guideline and is not specific to a certain use case.   For specific calculations for a customer's use case several different parameters need to be taken into account including their speed and oscillator tolerance.   The CAN spec has detailed equations to calculate this.  

    At 5kbps, they will have much more than 15 ns of tolerance, but for some more specific numbers I would need more information.

    1) What speed is the customer looking to use?

    2) Are they sourcing from a crystal?  What is the tolerance of the crystal?

    3) What is the total length of the CAN bus? 

  • 0 in reply to Y. Yang
    TI__Mastermind 25276 points

    Y. Yang said:
    1) What speed is the customer looking to use?

    Did not determine the speed yet, it will depends on end customer's usage. currently tested on Transmitter date rate at 5kbps and 1Mbps. 

    Y. Yang said:
    2) Are they sourcing from a crystal?  What is the tolerance of the crystal?

    20MHz 20pp and 22.5792MHz 20ppm crystal, the frequency is same as EVM.

    Y. Yang said:
    3) What is the total length of the CAN bus? 

    TX: DSP to transceiver 8500mil

    RX: DSP to transeiver 8000mil.

    transeciver to connector is 650mil

    Cable length is 20cm.

  • 0 in reply to Y. Yang
    TI__Mastermind 25276 points

    Yang, 

    Is there conclusion with those parameter?