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TCAN1042-Q1: The output is low for 2ms after waking up

Rogers Chen
Intellectual 825 points
Part Number: TCAN1042-Q1


Dear TI expert,

Our product uses TCAN1042-Q1 as the CAN transceiver, we found a problem during the test, after the 1042 is awakened, it will continue to output a low level of 2ms, which causes the receiver device to continue to report errors, we try to replace the same type of CAN transceiver from other manufacturers, there is no such problem, what is the cause of this problem? And how can this be solved? Many thanks!

  • 0
    TI__Guru 74322 points

    Rogers,

    The device should at most be taking 45us to transition to Normal mode from Standby, typically 9us. Can you share the STB pin state whenever this occurs? 

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Intellectual 825 points

    Hi Eric,

    PIN STB is pulled down to GND, following is the SCH:

  • 0 in reply to Rogers Chen
    TI__Guru 74322 points

    Rogers,

    By awakened do you mean powering up? If Standby is always pulled low, then the device will never go into Standby mode thus won't ever need to respond to a wake-up request. Can you share the exact procedure of your test?

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Intellectual 825 points

    Hi Eric,

    Yes, maybe I'm not right, in fact, after powering on TCAN1042 it will start sending data to the next node, but there will always be a dominant level of 2ms, and then it can communicate normally. In terms of the length of time, this seems to be causing an explicit timeout, am I right? If so, why is this the problem? We don't have this problem when we use TJA1042.

  • 0 in reply to Rogers Chen
    TI__Guru* 75871 points

    Hi Rogers,

    Eric is out of the office on travel, I am going to reassign this thread to one of our other experts. They should get back to you by next week. Sorry for the delay.

    -Bobby

  • +1 in reply to BOBBY
    TI__Mastermind 26826 points

    Rogers,

    Apologies for the delay; I'll cover here while Eric is out.

    You're correct to identify the dominant time-out period as the likely culprit for why this dominant signal lasts so long. Do you know what the start-up time is for your MCU or controller? The dominant time-out is a feature designed to prevent a node from locking up communication if the TXD pin is locked low, as may be the case here.

    The TCAN1042-Q1 uses TXD as an input to determine what is transmitted on CANH/CANL. If you have a second channel, it would be much more helpful to see TXD on this same waveform. It could help us confirm whether TXD is being held low indefinitely.

    When floating, the TXD pin has a weak pull-up characteristic to help bias the TXD pin away from a dominant state. It does not otherwise have the capability to pull TXD low, so this would likely be a function of the controller or some other pull-down that's present on CAN_TX_ISO. Is this net possibly connected to a digital isolator that might be biasing the net to LOW for startup? If stronger than a few microamps, then it could be the culprit.

    Best,

    Danny