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Original question:

TCAN4550: ISO16845 document

TCAN4550: Worst case test condition

Charles Zhang1
Expert 3430 points
Part Number: TCAN4550

Hi Team,

What's the worst condition for CAN signal integrity in a system(e.g., longest signal path, maximum ambient temperature, etc)?

Regards,

  • +1
    TI__Guru 53555 points

    Hi Charles,

    There are a lot of variables that play a role in signal integrity, so it is difficult to define a single worst-case condition. Generally, the longer and more complex (more nodes, branches, and stubs) a cable network it, the more prone it is to introduce long delays, significant paracitics, and ringing. Ideally the cable harness is as linear (daisy chain each node) and short as possible. Some larger networks can be accommodated by lowering the data rate used in the system. Lower frequencies are less sensitive to propagation delays and cable paracitics. They also introduce less high-frequency energy which is more likely to ring in the system. For more detailed info, I recommend this app note which contains a section on Bus Length vs Signaling Rate. 

    Regarding temperature, this is defined in the datasheet parameters. Generally, performance of electronics degrades the further they get from room temperature. We grantee all datasheet parameters will remain within specified limits as long as all listed operating conditions (such as ambient temperature) are within listed ranges. 

    Let me know if you have any more questions.

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Expert 3430 points

    Hi Eric,

    Thanks for your reply, besides, I would like to learn if there is any tool to calculate cable parasitic.

    Regards, 

  • 0 in reply to Charles Zhang1
    TI__Guru 53555 points

    Hi Charles,

    I'm not familiar with any specific tools for this, but most cabling I have seen includes its characteristic impedance and nominal capacitance (per unit length) in its documentation. Adding components to the cabling such as splices, connectors, and boards will increase the complexity of the network as impedances changes and unterminated end-points are introduced. The best way to determine how a given system will react to a signal is to test it physically as it is nearly impossible to account for every variable for perfect calculation. For designing, it is a good idea to follow best practices to avoid adding unnecessary complexity to the system. Examples would be to use a daisy-chain layout (no stubs), termination at end-points that match cable impedance (120-ohms typical), match PCB trace impedance with cable impedance, avoid splicing cables, etc. 

    Let me know if there's anything in this response you have questions about. 

    Regards,
    Eric Schott