LTC2875A CAN transceiver Failure mode

Hello,

I would like to know qhich Failure mode on CAN transceiver can lead to be in a fixed dominant status (leading to a max consumption continuously)

It seems that this transceiver has a protection (timeout) against stucking in dominant status.

thank you

Regards,

Sebastien

Parents
  • +1
    •  Analog Employees 
    on May 6, 2021 5:31 PM

    Hi Sabastian, 

    Its true the dominant state is higher power, but the larger concern may be a continuous dominant state blocking CAN bus traffic. Other nodes cannot overwrite the dominant state on the bus if the condition is allowed to persist.

    Typical causes of the CAN transceiver's TXD seeing a low improperly (and transmitting a dominant state) may be short in duration like a microcontroller start-up or supply sequencing issue where the TXD input pin floats. This is a reason the LTC2875 TXD input has an integrated 500k pull-up to VCC.

    Longer events might be a failure of the CAN controller, either hardware or perhaps a programming/user-error related issue. It could also be a mechanical issue, caused by debris or a contaminant on the PCB shorting the TXD trace to local gnd. For either case, the LTC2875 has the Dominant Timeout feature to prevent the node from indefinitely blocking CAN bus traffic. 

    Regards,

    Jason  

Reply
  • +1
    •  Analog Employees 
    on May 6, 2021 5:31 PM

    Hi Sabastian, 

    Its true the dominant state is higher power, but the larger concern may be a continuous dominant state blocking CAN bus traffic. Other nodes cannot overwrite the dominant state on the bus if the condition is allowed to persist.

    Typical causes of the CAN transceiver's TXD seeing a low improperly (and transmitting a dominant state) may be short in duration like a microcontroller start-up or supply sequencing issue where the TXD input pin floats. This is a reason the LTC2875 TXD input has an integrated 500k pull-up to VCC.

    Longer events might be a failure of the CAN controller, either hardware or perhaps a programming/user-error related issue. It could also be a mechanical issue, caused by debris or a contaminant on the PCB shorting the TXD trace to local gnd. For either case, the LTC2875 has the Dominant Timeout feature to prevent the node from indefinitely blocking CAN bus traffic. 

    Regards,

    Jason  

Children
  • Hi Jason,

    Thank you for the answer.

    In datasheet, Ios (bus output short circuit current) is given at 100mA max.

    Could you give me conditions to have this current? short cicruit between CAN H and CANL, short circuit between CANH/L and  GND or supply voltage?

    My concern is to know which failuere mode can lead to have a current consumption (steady state) . In our design, for safety reason, we have provisioned a overcurrent function on the transceiver power supply, but we don't know which kind of failure (realistic)  can lead to have the max current.

    Thank you

    regards

    sebastien