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TCAN334: CAN Bus Reference (CAN_GND) and Chassis Ground Guidance

Gideon Kanikevich
Prodigy 40 points
Part Number: TCAN334

Tool/software:

Hoping to get get some guidance on correct grounding for a CAN Bus I have designed. The following diagram gives a high level overview of the system connectivity:

Some notes on the setup:

  1. There are a total of 12 nodes, I've only drawn 4 in the interest of repetition.
  2. Each node is a custom designed PCB.
  3. Each node has an onboard DC-DC SMPS which powers the MCU, CAN transceiver and applicable on-board peripherals. These all share the same common ground (labelled 0V) in the diagram.
  4. CAN_H and CAN_L are twisted pair.
  5. CAN reference (CAN_GND) is the 0V system ground.
  6. Each node has mounting holes tied to 0V net, which directly tie the PCB to the chassis, indicated by the chassis ground on each node.
  7. Single Board Computer has its ground reference tied to the chassis.
  8. Pump 1 and Pump 2 are simply turned on/off via a MOSFET.

I believe this may be creating a ground loop as I am connecting 0V between each node via the power cable as well as connecting each nodes 0V net to the chassis.

I am seeing quite a clean CAN signal when running on the bench (with no chassis connection). Inside the chassis, there's a significant amount of extra noise visible on the signals.

I'm looking for guidance on best practice on how I should be running both the CAN reference as well as how the nodes should be tied to the chassis. I.e. should all the nodes and devices powered by those nodes all be connected to the chassis?

Thanks in advance!

  • 0
    TI__Genius 11055 points

    Hi Gideon,

    Generally connecting all nodes to a common ground should be fine, and CAN transceivers have the capability to handle ground shifts or faults that are possible within a system. But since you mention the extra noise from the chassis, I would like to ask is there common mode choke (CMC) used in your design? CMC can help with emissions from the transceiver, and also noise from the CAN bus to the transceiver. The CMC filters high-frequency noise and can help with voltage transients from the CAN bus. So if you expect the application to have a large amount of noise from other devices, like SMPS, oscillators, MCUs, motors, etc. I would highly recommend placing a CMC between CAN bus pins and terminations.

    In addition, placing filter capacitors (typically 100pF) near the connector can help to reduce the noise as well. I would also like to ask if that 120 Ohms is the only termination on the bus? Is there any other end of the bus needs termination? Please note that CAN requires termination value to be 60 Ohms to work.

    Regards,

    Sean