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TCAN1042-Q1: Please check the location of resistor.

Chase Jeong
Mastermind 7965 points
Part Number: TCAN1042-Q1


Dear TI experts,

My customer asked the location of resistors in communication line. Could you check that which one is right for case 1 and case 2?

Case1) 250Kbps communication speed.

1-1. 120ohm resistors are located in the start and end of communication line, and also located in each slaves.

1-2. 120ohm resistors are ONLY located in the start and end of communication line.

1-3. 120ohm resistors are located in the start of communication line, and also located in each slaves. (not located in the end of communication line.)


Case2) 500Kbps communication speed.

2-1. 120ohm resistors are located in the start and end of communication line, and also located in each slaves.

2-2. 120ohm resistors are ONLY located in the start and end of communication line.

2-3. 120ohm resistors are located in each slaves. (not located in the start and end of communication line.)

Please check that which one is right.

Best regards,

Chase

 

  • 0
    TI__Guru 74322 points

    Chase,

    The overall impedance of the CAN bus should be as close to 60 ohms as possible. This is typically met by putting 120 ohms at each end of the bus so that the parallel combination is 60 ohms. You can add higher-valued resistors at middle nodes to mitigate any signal reflections introduced by stubs, but having 120 ohms at each node will reduce the overall impedance to below what the driver can handle.

    For Case 1, option 3 would be your best solution, though you could put the 120 ohm resistor at the end of the bus closer to Slave 3. For Case 2, I'd recommend option 2 but just put both of those terminating resistors at Master and slave 3 node. This will decrease the length of your bus, removing unnecessary cable length.

    Please let us know if you have any other questions.

    Regards,

    Eric Hackett