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AM2634: CAN communication

David Huang
Intellectual 2285 points
Part Number: AM2634
Other Parts Discussed in Thread: TCAN1044-Q1, ISO6721

Hi team,

My customer is planning on using AM2634 in their new design, where they will use CAN wake up function to wake up the PMIC before putting the MCU in working state.

For this setup, the CAN IC needs to be powered up first, and then output the wakeup sequence through the Tx Rx. This will create logic high voltage on the Tx and Rx line before the AM2634 is powered up.

Could anyone let me know that is it safe to put the CAN Tx Rx line high before AM2634 is powered up?

Regards,

  • 0
    TI__Guru**** 197426 points

    Hi David,

    Appling voltage to one pin when the MCU is unpowered is not recommended. 

    The ESD diodes draw current if the main power supply is off and CAN TX/RX pins are powered. This current flow has the side effect that the MCU might be powered up backwards through the ESD diodes. This is not the intended powering scheme for MCU and can lead to erroneous and unpredictable behavior, because the powering path is not the expected one and a current limitation is given by the ESD diodes. In worst-case scenarios, this also can lead to physical damage of the device and cause a malfunction in the application.

    Can you use an isolated CAN transceiver? 

  • 0 in reply to QJ Wang
    TI__Intellectual 2285 points

    Hi QJ,

    Thanks for the response!

    Currently the customer is using TCAN1044-Q1, is there any other isolated CAN you suggest for the replacement?

    Also, if the goal is to prevent voltage applies on MCU before the power up, I think buffers or optocouplers would also work, is that correct?

    Regards,

  • 0 in reply to David Huang
    TI__Guru**** 197426 points

    Yes, you are correct. A isolation buffer does work, for example ISO6721