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TCAN1042GV-Q1: Muxed CANH/CANL

Mike Drake
Prodigy 90 points
Part Number: TCAN1042GV-Q1
Other Parts Discussed in Thread: SN74CB3Q3251, SN74CBT3251, SN74CBTLV3251, TCAN332

Any design examples/circuits for muxing CANH/CANL onto various pins?  I have a need to be able to drive these connections into various pins on the same connector.  It will never be switched at run-time, and this is only done at initialization to handle connection to different pinouts.  I need something on the order of a 2-to-12 mux in front of the transceiver.  This will also necessitate using discrete protection circuitry to protect the mux from bus faults.  Any guidance greatly appreciated.

  • 0
    TI__Guru 62920 points
    Hi Mike,

    I'm checking into this with our team that is responsible for analog muxes and signal switches. Do you know if your application needs to support the full CAN common-mode range of +/- 12 V? That requirement unfortunately limits the options available. If you don't need a wide common-mode range (e.g., if all the CAN nodes share the same ground reference potential), then finding a suitable multiplexer should be a little easier.

    Max
  • 0 in reply to Miguel Robertson
    Prodigy 90 points

    Hi Max,

    I appreciate you getting back to me. I have yet to test how much offset I have on all the buses (some of the devices are not mine), but the connector I am interfacing to does include a common signal GND among the devices. So, while there is likely to be some offset, I expect it to be much smaller than the -2V/+7V that is defined. I am operating under the assumption that if I can adequately clamp the CANH/CANL coming into the mux to stay within Abs Max (or preferably Rec Operating), that I may get away with this.

    Any concerns with noise spikes on the bus and latch up for a solution like this?

    As you look at muxes, I would be especially interested in small footprint and serially controlled devices. Also, any recommendations for protection circuitry would be greatly appreciated.

    Thanks,
    Mike

  • 0 in reply to Mike Drake
    TI__Guru 62920 points
    Mike,

    Here are a few recommendations on switches from our team:

    SN74CB3Q3251
    SN74CBT3251
    SN74CBTLV3251

    These are chosen based on the channel configuration you mentioned, support for the normal CAN signal voltage range (0 V to 5 V), and low on resistance (needed in order to prevent attenuation of CAN output signals being transmitted to a 60-Ohm bus).

    Noise and transients are something worth worrying about on any external port or cabled interface, so components like transient voltage suppressor (TVS) diodes and filtering capacitors (or even common-mode chokes) are common to see on CAN interfaces. Choosing robust transceivers can help reduce the need for these components, though - for example, devices like TCAN1042 (5-V powered) and TCAN332 (3.3-V powered) are rated for high levels of transient immunity (as shown primarily in their IEC 61000-4-2 ESD specs). The right protection scheme depends on the immunity levels you think you need for your application and operating environment, though.

    Max