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Controller Area Network (CAN) Transceiver protection and filtering circuit

Govindaraj Yadav
Prodigy 20 points


I have interfaced my DSP processor with the CAN transceiver SN65HVD233D for CAN communication and since my application is in very harsh environment I wanted to know whether there are some protection and filtering circuits to prevent my CAN transceiver to go bad and eliminate common mode noise.

  • 0
    TI__Mastermind 21911 points

    Hello,

    Yes there are. Below is a picture of all the typical protection devices and set-ups a CAN network will have (this comes from a portion of an evaluation board that I use). It can include both terminated nodes and unterminated nodes. Starting with the TVS (Transient Voltage Suppressor) diodes that are shown in blue. These are typically used to improve the system level ESD performance. A common diode that is used is the MMBZ27 diode. These diodes are actually part of a family of diodes that come with different clamping voltage that is indicated by the number at end.

    The diodes shown in black are dual zenor stack diodes that can be used to protect both the CANH and CANL pins with one device. A typical device use for this application is the PESD1CAN devices.

    Lastly, terminating the node with 2 resistors and a capacitor at the midpoint creates a filter for noise on the bus pins. It has a corner frequency shown below. If the CAN device used has a SPLIT pin (2.5 volts output), it can be tied to the midpoint to further stabilize the bus.

     

    Please let me know if you have any questions,

    John

  • 0 in reply to John Griffith
    Prodigy 20 points

    Hello John,

                          Thank you for your speedy response. I shall implement the circuit and shall come back to you in case I have any queries.

        

  • 0 in reply to Govindaraj Yadav
    TI__Mastermind 21911 points

    Govindaraj,

    You are very welcome. In addition capacitors are also placed on the CANH and CANL lines (also shown in picture above). This can help with ESD protection and Emissions as well. Typically OEMs allow between 40 - 100pF of capacitance. The more nodes, the longer cables, the capacitance of the protection diodes add, all take away from the maximum speed you can operate your system at. Therefore there are normally limits the OEMs mandate.

    John