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TCAN3414: Adding a selectable terminator resistor with a split termination

jan stappers
Prodigy 20 points
Part Number: TCAN3414


We currently have a design with the TCAN3414. We would like to change the termination resistor to a split termination and with a switch to enable or disable the terminator. This switch can de mechanical or a mosfet. Does someone have recommendations on how to approach this? I have seen that there is an application note on how to use mosfets for a regular termination resistor, but it is not clearly explained for split termination.

Our old approach is like this:

image.png

  • 0
    Guru 319620 points

    You need two switches to disconnect both signal lines from the capacitor.

    In theory, the CAN bus allows quite high offset voltages between nodes; I do not know what voltages happen on your buses in practice. The simplest solution while allowing voltages beyond the supply rails would be mechanical switches.

  • 0 in reply to Clemens Ladisch
    Prodigy 20 points

    Hi,

    Ok, we can use double pole switches for that. But is this a good practice to use a mechanical switch? Or is this not a good method?
    The bus voltage is in normal operation max 5V, when there is a bus fault it is max 48V.

  • 0 in reply to jan stappers
    TI__Guru 60477 points

    Hi Jan,

    If you want “termination OFF,” I would further recommend to avoid leaving any unintended path from CANH / CANL to the midpoint capacitor (otherwise you may create a weird common-mode load that could inject noise).

    Hence, would recommend disconnecting the whole terminator from the bus. Where when OFF, the entire split network is floating and the capacitor is isolated.

      • R_H from CANH → Vmid

      • R_L from CANL → Vmid

      • C_mid from Vmid → GND

    • Then, may add two series switches; one in series with CANH branch and one in series with CANL branch, upstream of the resistors, thanks.

    Best Regards,

    Michael.