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Original question:

ISO1042: connection issue

ISO1042: Design review

Stefano Marrazza
Prodigy 145 points
Part Number: ISO1042
Other Parts Discussed in Thread: SN65HVD230

Tool/software:

Dear Technical support,

following a previous thread on this forum (https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/1433410/iso1042-connection-issue?tisearch=e2e-sitesearch&keymatch=iso1042#.), we design the an isolated CAN node using the configuration reported in the picture below:

                                     

U8 + U4 compose an isolated CAN node (ESC_CAN_H, ESC_CAN_L), and the microcontroller is connected on D and R ports of U7.

This configuration doesn't works unless I remove R94: in this case the non isolated CAN (CAN_H, CAN_L), works properly but the isolated CAN (ESC_CAN_H, ESC_CAN_L) doesn't works.

I removed R94 and R95 in order to disconnect U4 from U8 and I disconnect the microcontroller from U7 and I connect directly TXD and RXD from microcontroller directly on ports RXD and TXD of U4: in this case the isolated CAN (ESC_CAN_H, ESC_CAN_L) works properly.

Do you see some mistakes in the designed configuration? Do you have suggestion concerning the problem or other thest I could do?

Many thanks, best regards

Stefano

  • 0
    TI__Mastermind 31455 points

    Hi Stefano, 

    I am very sorry for the confusion the previous post has caused. CAN transceivers cannot connect the logic sides together without an MCU in between to decode and retransmit the message. 

    This is because the CAN-bus transmission will continuously read the state of the bus and then retransmit it. This causes a lock-out condition of the bus. Disconnecting R94 allows unidirectional communication from the ESC-bus to the main-bus, however since the D pin is disconnected the reverse communication is not possible. 

    I did take a look at the SN65HVD230. These transceivers have a "listen only" mode. Pin 8 of both transceivers can be toggled to opposite states to create a listen only mode and avoid a lock up of the bus.  

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 145 points

    Hi Andrew,

    thank you for your reply.

    In order to use the board and to proceed with the other planned tests, I am going to remove the isolated CAN node and connect directly on CAN_H and CAN_L.

    In order to do this I am going to remove the isolated ground and realize one single ground on the whole board.

    On the same board I have two IC for isolted current and voltage measuremets as reported in the pictures below:

                                   

    Is it ok or problems could arise shorting the ground togheter?

    Thank you, regards

    Stefano

  • 0 in reply to Stefano Marrazza
    TI__Mastermind 31455 points

    Hello Stefano, 

    For most isolated devices the grounds can be shorted together with no issues. This does, however, bypass the isolation in the system. Please reach out to each team by creating a new E2E with device in the title.

    Best,
    Andrew