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Original question:

TCAN1043-Q1: How to wake up a sleeping device

TCAN1043-Q1: TCAN1043-Q1

kkkkk ys
Prodigy 80 points
Part Number: TCAN1043-Q1

Tool/software:

Hi, i have a question about can transciever's wake-up sequence.

Sorry if this is a basic question. I'm pretty new to CAN and this might be a more general CAN question, but I can't find the answer.

Q1. from block diagram,


once the can transciever's Vsup pin supplied, transciever goes to standby mode.
at standby mode,
1. CAN bus bias = autonomous(does it mean not designated CAN bus voltage?)
2. WAKE sources : WUP & LWU -> I don't understand this sentence meaning.
3. INH pin voltage level increase to Vsup level
4. SWE timer becomes active(=during SWE time, we can change mode(normal, sleep etc..)

Q2. why do we need wake-up? for what?
by Vsup pin, we can make transciever to standby mode.
transciever's mode can be adjusted by EN, Stb pin by MCU.
then, what is the role of wake-up??

  • +1
    TI__Guru 74262 points

    Kkkkk,

    kkkkk ys said:
    1. CAN bus bias = autonomous(does it mean not designated CAN bus voltage?)

    This means that the bus will be biased to GND unless there is CAN traffic. At that point, the CAN bus will be biased to 2.5V.

    kkkkk ys said:
    2. WAKE sources : WUP & LWU -> I don't understand this sentence meaning.

    This means that while CAN communication isn't possible in Standby mode, a wake event like LWU (local wake up, using the WAKE pin) or a WUP (wake-up pulse, CAN bus wake-up) will cause RXD to toggle low, indicating a wake event has occurred.

    kkkkk ys said:
    3. INH pin voltage level increase to Vsup level

    INH is in a low state in Sleep mode, but pulled up to VSUP in every other mode.

    kkkkk ys said:
    4. SWE timer becomes active(=during SWE time, we can change mode(normal, sleep etc..)

    This is a 4-minute timer that once elapsed, will transition the device to Sleep mode. If the device is transitioned to Normal mode, this timer will stop.

    kkkkk ys said:
    Q2. why do we need wake-up? for what?
    by Vsup pin, we can make transciever to standby mode.
    transciever's mode can be adjusted by EN, Stb pin by MCU.
    then, what is the role of wake-up??

    Typically when the transceiver is in Sleep mode, so is the rest of the system surrounding it. Meaning the MCU, the power supply, etc. If the MCU is asleep, then EN and nSTB cannot be controlled. So, a wake on the CAN bus from another CAN node, or a wake on the WAKE pin using the battery or a switch connected to the battery can be used to wake the device, transitioning it to Standby mode automatically. This drive INH high, and in a lot of systems, INH is used as an enable for the power supply for the MCU and VIO and/or VCC for the CAN transceiver.

    So, as you can see, the CAN transceiver can be used to wake the entire system.

    Regards,

    Eric Hackett