Repeater solution

Hello,

I would be happy to help you debug this situation. I would like to start by asking some questions first:

(1) As I understand it, you monitor the R_CANH, R_CANL nodes and while applying a signal from a connected slave/device at the R_CANH_RP1 and R_CANL_RP1 side of the board, but you do not see any signal at R_CANH and R_CANL. Is that correct?

(2) Voltage measured between R_CANH_RP1 and R_CANL_RP1, when the bus is static/not switching, is less than 1.5V.  Is that correct? What is the voltage that you are measuring?

(3) How many slave devices are connected to the bus (R_CANH_RP1, R_CANL_RP1) lines?

If you could, a scope shot of the incoming signal, RXD, and TXD pins for that device would be very helpful.

Thank you,

Shasta

Hello ShataThomas,

1) Yes, I am trying to send a data from one end of the device to other end with this repeater-based approach but i am not able to send/receive any data if i connect this transceiver in this way.

2)The Voltage measured is attached in the image.

3)I have connected only one device to check the capability.

Hello,

Thank you for this clarification. I believe that the issue here is the TX and RX connections. The LTC2875 (and most CAN transceivers) have an internal loopback functionality that is always enabled that is going to cause a problem here.

For example, in your circuit, you have a signal coming in from one side - let's call that side A. The RX output of the A-side LTC2875 is connected to the TX input on the B-side LTC2875 and the B-side transceiver begins to transmit the message across.  However, as the message is transmitted, the B-side RX pin also toggles, sending data back to the A-side LTC2875 which then also tries to toggle the bus lines.  This would result in bus contention and both the incoming and outgoing messages being corrupted.

Some arbitration logic needs to be inserted between the TXD and RXD pins of the transceivers to account for which direction the data is travelling. Unfortunately, ADI does not have a reference design for this application, but the CAN in Automation website has some technical references that might prove helpful.

Thank you,

Shasta 

Hi Shasta, 

That was really helpful, if possible, can you share the reference Doc's for this arbitration logic that will have added advantage for my design.

Hello,

Unfortunately, ADI does not have a reference design for this type of design/solution. I suggest a quick Google search - I did see some schematics from other vendors that may prove helpful.

Thank you,

Shasta