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TCAN1051HGV: designing with TCAN1051HGVDR

Sv
Intellectual 555 points
Part Number: TCAN1051HGV

Tool/software:

Hello Team,
We are using the CAN transceiver TCAN1051HGVDR in one of our projects.
The block diagram is as shown below.

We have CAN between board 1 and board 2.
Both the boards are powered from different power supply.
1). Do we need GND signal running between Board 1 and Board 2.
Since CAN is differential signalling, the CAN H will be referring to CAN L.
Please correct me if I am wrong.
2). So can I use a simple 2 wire twisted pair cable for CAN H and CAN L lines?.
3). Do we need GND also running from Board 1 to Board 2 as a common reference?.

Looking for your reply.

  • 0
    Guru 317250 points

    CAN is differential, but the voltages on CANH and CANL are measured relative to GND. The common-mode range is ±30 V; if it is possible to have a larger ground shift, then you have to force it lower with a GND line, or use isolated CAN transceivers.

  • 0
    TI__Guru 53575 points

    Thanks Clemens!

    Hi Sv,

    An extra cable for a ground connection is not required for the differential signal to be successfully transmitted between nodes so long as the common mode range is not violated at any transceiver. As Clemens points out, if the expected ground shift between nodes is within this common mode range, then you should have no issue when only CANH and CANL are connected between the boards. 

    Let me know if you have any more questions. 

    Regards, 
    Eric Schott

  • 0
    TI__Mastermind 28310 points

    Hi Sv

    Clemens is correct, CAN is designed to handle ground shift. For this device the common mode range is between -30 to 30V. If there's case you would like to add a different transceiver on the node, make sure the common mode voltage is within its specification.

    Regards,

    Sean

  • 0 in reply to Eric Schott1
    Intellectual 555 points

    Hello Team,
    Thank you for your reply.
    Usually for a differential amplifiers, the differential voltage is taken as the voltage at one node minus the voltage at the second node.
    So Vcandiff = Vcanh - Vcanl
    Please correct me if I am wrong.
    So in order to measure the Vcanh or Vcanl voltage we need a common ground between them.
    If we have no common GND, it will be like measuring voltage of a battery with a multi meter keeping one of the probe is connected to the battery +ve and the other probe left floating in the  air.
    Please correct me if I am wrong.
    For MSO also, to measure differential voltage, we usually don't connect the GND pin. We only connect the A and B pin of the differential probe.
    If we use an isolated CAN transceiver like ISO1042BDWR, there is a GND pin at the secondary side of the IC. So we have to use another set of wire to transfer the secondary side voltage from board 1 to board 2

    Looking for your reply

  • 0 in reply to Sv
    TI__Guru 73591 points
    Sv said:
    Usually for a differential amplifiers, the differential voltage is taken as the voltage at one node minus the voltage at the second node.
    So Vcandiff = Vcanh - Vcanl
    Please correct me if I am wrong.

    Yes the dominant state for CAN is measured by VOD = VcanH-VcanL. It doesn't use a difference amplifier though. Current flowing from CANH into the termination resistor into CANL will generate a positive Vcandiff or VOD. 

    Sv said:
    So in order to measure the Vcanh or Vcanl voltage we need a common ground between them.
    If we have no common GND, it will be like measuring voltage of a battery with a multi meter keeping one of the probe is connected to the battery +ve and the other probe left floating in the  air.
    Please correct me if I am wrong.

    You're looking at the difference voltage between the CANH and CANL pins so the DC bias is subtracted out of the calculation. So the GND reference doesn't need to be the same between the two boards.

    Making up an example case here of how GND differences can still transmit acceptable VoD signals: If the CANH is 6V and CANL is 4V (VOD=2V) on the transmission point by the receive point has a different GND potential and sees CANH is 8V and CANL is 6V (VOD is still 2V) then the receiver will see the signal is as dominant even though the GND is not the same reference point.

    Eric may comment further if you have additional questions or to add comments to my response.

    -Bobby