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TCAN1044A-Q1: Confirming 1044A questions

Fredy Zhang
Expert 5320 points

Part Number: TCAN1044A-Q1

Dear Expert: 

it's using the TCAN1044AVDRBRQ1 CAN transceiver in a 14V-powered controller. However, some of the external devices communicating with our system may be powered by 28V supplies. Therefore, we have a few questions that we would like to confirm for 28V system: 
 
1. If CANH is shorted to the 28V supply, can the CAN communication still function normally?
The datasheet specifies a common-mode voltage (Vcm) range of ±12V.  
2. If CANH and CANL are each shorted to a 30.3V supply, will the transceiver be damaged?
The datasheet lists the maximum differential voltage tolerance as 45V. IO ±58V. 
3. If CANH and CANL are each shorted to a 30.3V supply. will the transceiver be damaged?
4. If CANH and CANL are shorted to ground and 30.3V respectively, this will impose higher requirements on the overcurrent capability of the external common-mode choke and the power rating of the termination resistors. Do you have any recommended specifications or parameters for these components?

Regards,

Fredy Zhang 

 

  • 0
    TI__Guru 73962 points

    Hi Fredy,

    1. Yes, if there is enough differential between CANH and CANL. However, note that this should be a fault and the controller may be configured to handle faulty communications. I.e., the ±12V common-mode spec should be referring to the recommended operating range for compliant signaling and the device may continue operating during certain fault scenarios dependent on system-level robustness such as topology, termination, grounding, cable characteristics, etc. Hence, the CAN controller should be configured to handle potential communication faults (for example using bus-off recovery mechanisms).

    2 and 3. Note that the IO should be for 6 V per the abs max rating and VBUS for 58 V. However, damages are common only if the abs max rating is exceeded. I.e., the bus pins support high fault-voltage tolerance (up to the specified bus fault protection limits). Since both CANH and CANL are at approximately the same potential, the differential voltage remains near 0V and within the data sheet's limit. However, care should be taken with system parasitics such as cable inductance, common-mode chokes, and transient events, since these can generate overshoot or ringing that may exceed the absolute maximum ratings. See this appnote. May further validate the peak voltages observed per their system environment.

    4. The IOS spec should still be the same I.e., the overcurrent capability should be limited by the IOS spec and can be used. For example, P = I^2 * R = (57.5 mA)^2 * (60 Ohms) = 0.1984 W (≥ 0.25 W rated component can be then used), where that 57.5 mA is half of the 115 mA maximum dominant bus fault current split on two terminations. For the CMC, automotive-qualified chokes should suffice, where the saturation current should already exceed the possible IOS current just fine, thanks.

    Best Regards,

    Michael.