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SN65HVD233: Can I use the transceiver as shown in the attached picture below?

Adnan Hussain
Prodigy 30 points
Part Number: SN65HVD233
Other Parts Discussed in Thread: SN65HVD234

I would like to use three of these transceivers and connect their CANH/CANL pins to three different CAN buses. Then I would like to multiplex the D and R pins of the three transceivers into a single D and R output to my CAN Controller. I would then control each transceivers by the LPK function via the MCU. All the three CAN buses would be active all the time but I would only choose to output a certain BUS data using the LPK to turn on the relevant transceiver. 

  • 0
    TI__Guru 50795 points

    Hi Adnan,

    When the SN65HVD233 device is in Loop-back mode, the D and R path remains active internally. In this configuration, if two of the devices were in this mode, they would both be driving the R line to the same state as the D line. This would disrupt any information the remaining device would try to relay from the CAN bus and the controller would not be able to see the information its sending looped back to it.
    I would recommend switching to a device with an Enable/Disable function. This would be much more likely to allow the active device to drive data on the RX line without interference from the inactive transceivers.
    The SN65HVD234 is a device with an EN feature in the same family as the SN65HVD233. However, since it is an older part, I do not have much information on how the controller side of the transceiver behaves when the device is disabled (pull-up activity is my main concern). Since the drivers on the R pin of this device are push-pull, they should be able to sink enough current to control the line in the case of two inactive transceivers, but this will become harder if more devices are added to the MUX configuration. If this is a concern, I would recommend a newer part with an EN function and more documented behavior to fit your needs.

    Let me know if you have any more questions.

    Regards,
    Eric

  • 0 in reply to Eric Schott1
    Prodigy 30 points

    Hi Eric,

    Thank you for your detailed insight. Please correct me if I am wrong, I should be looking for a transceiver, that has an EN function. More importantly, both the driver and the receiver should be turned off with bidirectional communication cut off? On the TI product page, I found three transceivers with SHUTDOWN mode that puts both the driver and receiver in OFF state. This is what it states "This is the lowest power mode of all of the devices. The CAN driver and receiver are turned off and bi-directional CAN communication is not possible. It is not possible to receive a remote wake request via the CAN bus in this mode. The CAN bus pins are pulled to GND during this mode" I am taking about this transceiver . Thank you

  • 0 in reply to Adnan Hussain
    TI__Guru 50795 points

    Hi Adnan,

    Yes, a method to disable the R pin of the receiver is essential for the ability to share the same trace and input to a controller.

    The condition of the driver portion of the device depends on the impact you're willing to have on the CAN lines while the transceiver is not active. If communication on the CAN lines only matters when your device has selected that particular transceiver (there are no other devices trying to communicate on that bus), a total shutdown mode that pulls the CAN bus to GND is fine. However, if you wish for external communication to continue on the non-selected CAN buses, the driver should be in a high-impedance state. This can be accomplished with an EN function (like with SN65HVD234) or by driving a receive state (D input = H). If you also with to share a trace with the D pins of these devices, the latter would not be an option without a buffering system to stop data inputs to the disabled transceivers.

    I hope this helps. Let me know if you would like more clarification or part suggestions.

    Regards,
    Eric