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SN65HVD234: CAN bus node spacing

Part Number: SN65HVD234
Other Parts Discussed in Thread: TCAN1042-Q1, TCAN1051-Q1, TCAN330G, TCAN332G

I read the TI app note SLLA279A on minimum distance between CAN nodes. The solution offered was to increase  the length of the cable joining the CAN nodes from 5 inches to 18 inches. Is there an approach that doesn't involve extending the cable? If you reduce the CAN bus speed, does that help? Could you add grounds to the cable to possibly increase its capacitance per unit length? Does TI have transceivers with smaller differential capacitance than the 65HVD234?

Thanks in advance.

  • Timothy,

    Yes, reducing the CAN speed would help this problem since the waveform would have more time to reach the threshold levels for each bit, and thus allow enough time for the nodes on the bus to interpret each bit individually. I'm not completely sure what you mean by adding grounds to the cable to increase the capacitance, but from my understanding, that would add to the lumped load capacitance and not the distributed capacitance due to the cable characteristic impedance.

    As for devices with less capacitance, the TCAN1042-Q1 and TCAN1051-Q1 have a bit less, typical is 12pF. However, neither of these devices have an Rs (slope control) pin, so if that's necessary for your application, they won't be suitable. What specific needs do you need with the CAN transceiver, why was SN65HVD234 chosen?

    Regards,
  • Hi Eric,
    Thanks for your response. The SN65HVD234 was chosen for several past generation designs, but I'm not sure why - the slope control was not employed nor was the sleep mode. I'm looking at a new design and I want to make sure I don't violate the bus spacing requirement. I want the device to run from 3.3V, so I think that one of the devices in the TCAN330G family seem to be a good candidate - differential capacitance is listed at 10pf max. Should the TCAN332G be able to do everything that the SN65HVD234 could do (given that we didn't use the 234's slope control or the sleep mode and ran it off 3.3V)?
  • Timothy,

    Yes, it is a fully capable 3.3V CAN transceiver, which sounds like is all you need.

    What kind of application is this, and how many transceivers do you expect in the system?

    Regards,
  • Thanks for your response. It is an automation application. In this current application, I have 4 CAN nodes; future products might have as many as 7.