Hello,
I'm working on the spec for an electric vehicle 3-phase inverter and I'm trying to determine whether or not a isolated CAN bus is required. The traction system and low voltage system will be galvanically isolated - isolated gate driver ICs, voltage/current/temp sensors, etc will be used. I understand a isolated CAN transceiver is not required for functionality, but will it improve EMC and protection, correct? Can anyone elaborate and shed some light on this?
Thanks!
JSly,
Here is a helpful document and a section that addresses your question. This is also followed by my own comments.
"The CAN standard ISO11898-2(2016) requires ±12 V common mode voltage range support for a compliant CAN transceiver. This means a CAN receiver needs to tolerate up to ±12 V common mode voltage on CAN lines with respect to bus-side ground and still be able to faithfully replicate differential voltage transitions on the bus. There are CAN transceivers available from TI, such as TCAN1042, which support an extended common mode range of up to ±30 V. When the communicating nodes in a CAN network have larger ground potential differences (GPDs), which are higher than the supported common mode voltage range of the transceiver, due to longer communication distance or system ground being noisy (such as in motor drive applications), isolating the CAN node becomes necessary. The isolation barrier also acts as high impedance to common mode noise transients (such as ESD/EFT/Surge) that are common in industrial environments. Proper design in some application scenarios can enable system designers to drop all common mode noise across the isolation barrier, thereby eliminating some external components commonly seen on CAN bus"
Generally an IEC or automotive standard will dictate the use of isolation in the design. Besides that, isolation overcomes needing to communicate to nodes with different ground potential differences (breaking ground loops) or to communicate with devices on the high-voltage side of the system. You wouldn't want something the user touches (throttle, buttons, gauges, etc) to have electrical path to something of high voltage( BMS, inverter power stage, high-side sensors, etc). Isolation then breaks this path and preserves safety. This also helps keep the high-power transients in an automotive system such as those from motor startup or high-current charging from entering into the control side of the system.
Respectfully,
Lucas Schulte
