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TCAN1145-Q1: VSUP for truck 24V system application

Zehui Li
Intellectual 440 points
Part Number: TCAN1145-Q1
Other Parts Discussed in Thread: TCAN1043, ISO6762, ISO1042

Hi,

  Voltage capability of VSUP max rating 42V is not enough for truck 24V system. How to deal with the problem?

  • 0
    TI__Mastermind 49975 points

    Hi Zehui,

    Unfortunately there is no way to increase the bus fault tolerance of a CAN system if the transceiver is not able to supply the required voltage. In order to support a 24V system with load dump conditions, a device with higher bus fault protection such as TCAN1042 or TCAN1043 would need to be used. We currently do not offer a device with ±70V bus fault rating that also supports partial networking (nor am I aware of such a device available on the market elsewhere). There may be a way to meet this requirement with the TCAN1145 with the addition of digital isolation, but this will drastically increase the solution size, cost, and complexity. Let me know if are interested in discussing this possibility further. 

    Regards, 
    Eric Schott 

  • 0 in reply to Eric Schott1
    Intellectual 440 points

    Hi Eric，

        I am interested. Could you share your ideas?

  • 0 in reply to Eric Schott1
    Intellectual 440 points

    Is it possible to use simple circuit to be compatible rather than a pre-regulator for VSUP? 

  • 0 in reply to Zehui Li
    TI__Mastermind 49975 points

    Hi Zehui,

    The solution I am thinking of involves using a digital isolator such as the ISO6762 to isolate the digital signals of the TCAN1145 from the processor. This would allow the CAN bus side to withstand several kV worth a difference from the local ground of the node. If there were to be a fault on the CAN bus, the transceiver may not see the whole voltage differential across the CAN pin to ground due to the isolation between them. 

    The main downsides to this solution would be 1) size as isolation requires a considerable amount of board space and 2) cost as the digital isolator and needed isolated power solution would add to the BOM. 

    Is this solution something you would be interested in perusing for this application? 

    Regards,
    Eric Schott 

  • 0 in reply to Eric Schott1
    Intellectual 440 points

    Hi Eric,

       That's a problem indeed. But I'm more worried about TCAN1145 itself. Even if we use a TVS to protect the system, the 42V limiting value is still too low, which is lower than the clamp voltalge.

  • 0 in reply to Zehui Li
    TI__Mastermind 49975 points

    Hi Zehui,

    In this case what we are concerned about is the possibility of a DC fault from the battery line to the CAN bus during a load dump condition where the battery  voltage can be more than 2x the nominal level. A TVS diode is not sufficient to protect from this condition since the long exposure time will cause the diode to burn out. The only solution to survive this case is to have the transceiver pins be rated for the DC voltage we are trying to withstand, or change the ground reference of the transceiver so the DC fault does not appear as harsh. Because there are currently no partial networking capable transceivers that have a bus fault rating of ±70V, I think the isolated solution is the only practical way to accomplish this. 

    If the partial networking function is not a requirement here, it would be simpler to use a standard TCAN1043 transceiver which is rated for ±70V bus faults which is sufficient for 24V battery applications. 

    Regards,
    Eric Schott 

  • 0 in reply to Eric Schott1
    Intellectual 440 points

    Hi Eric,

         In fact, partial networking function is the reason why we choose TCAN1145. It's not hard to change to TCAN1043. Does you have a detailed application about isolated solution?

  • 0 in reply to Zehui Li
    TI__Mastermind 49975 points

    Hi Zehui,

    We have a reference design that goes over the basics of implementing isolation in a CAN network. This design uses the ISO1042 which integrates both the CAN transceiver and digital isolator in the same device. The same methodology can be used for a discrete isolator with the TCAN1145 to enable partial networking in the system. 

    Let me know if you have any questions on this reference design. 

    Regards,
    Eric Schott