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ISO1044: Have we tested ISO1044 + OptoMOS solution and the intention of using optocoupler?

Bowen Ling
Intellectual 1410 points
Part Number: ISO1044

Hi team,

Happy New Year!

My customer now has some questions when reading Top Design Questions about Isolating CAN Nodes Bus Design (Rev. A).(SLLA486A)

In section 4,

Q1: Have we tested this solution in lab or in real application?

Q2: What is the purpose that we recommend an optocoupler? For isolation purpose in combination with ISO1044 or to match the resistor. 120Ohm mainly uses for impedance matching, does the OptoMos(photorelay) also has this function? 

Thanks!

Best Regards,

Bowen

  • 0
    TI__Mastermind 29265 points

    Hello Bowen, 

    Happy new year to you too and hopefully that article helped get you started with CAN. 

    1. The circuit shown in figure 4-2 is a fairly common industry solution there should not be any issues using this set up with ISO1044. 
    2. The purpose of the OptoMOS in this circuit is to allow an isolated signal to connect/disconnect the 120-ohm termination resistor. This is a useful feature if you are expecting CAN nodes to be added or removed in operation. 
      1. A more detailed explanation is in the paragraph above these figures "The two farthest end nodes in the network can drive TERM=High to enable termination of 120 ohm across the bus, while all other nodes can drive TERM=Low. This way the CAN bus effective termination is 60 ohm (120 ohm on both ends in parallel); while the hardware design of each node can be the same." 

    Let me know if you have further questions. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Intellectual 1410 points

    Hi Andrew,

    Thanks for replying.

    Do we have non-isolated solution for this application? Or this must use isolated solution like OptoMOS?

    Thanks.

    Best Regards,

    Bowen

  • +1 in reply to Bowen Ling
    TI__Mastermind 29265 points

    Hello Bowen, 

    You must use an isolated solution for controlling the resistor when working with ISO1044 in order to maintain isolation performance. However, if isolation is not needed in your system, you can use a non-isolated CAN transceiver like TCAN1044 to enable/disable the termination resistance.

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Intellectual 1410 points

    Thank you, Andrew!