Are 5V and 3.3V CAN Transceivers compatible?

CAN transceiver is widely used in automotive and industrial domains. Can Transceivers help map the Data link layer to the physical layer and all the CAN transceivers comply to the 11898 standard.  The transceivers comply to these Medium Access unit standards. There are different variations within the 111898 standard which define the specifications of the bus like the speed and electrical levels. When we talk about the electrical levels and the CAN transceivers, we should be aware of the different options available in the market. A clear understanding is always important before selecting the CAN transceiver. The CAN transceiver is selected based on the below criteria:

• Power supply available on the board (5V or 3.3V). Can't have a separate supply only for CAN and this adds cost and complexity
• Isolation required 
• CAN speed required
• ESD requirements - some CAN transceivers have internal ESD protection
• Processor side logic levels of the CAN signals
• Common mode signal range
• Power Dissipation
• Fault Protection on the CAN lines
• Mode control 
• Stand-by mode option
• Loop back control option

While we talk about 5V and 3.3V transceivers, there shall be cases where nodes with 5V and 3.3V supplied transceivers have to be connected. This raises the question whether these two can be connected or shall there be any incompatibility. To answer this question, 5V and 3.3V transceivers are always compatible w.r.t electrical levels and they can be connected together within the same CAN network. We shall look at how the electrical levels are compatible.

For this, we need to understand the Recessive and Dominant states of the CAN bus. For a logic HIGH which is called Recessive state, the difference between CANH and CANL is '0'. For a logic LOW which is called dominant state, the difference between CANH and CANL is >=1.5V. 

The above signalling for logic HIGH and logic LOW is the same whether it is 5V or 3.3V transceivers. So, a CAN device across the network need not be worried about the CAN transceiver operating voltage as irrespective of voltage of operation, they can receive and decode the voltage. The common mode voltage for 5V and 3.3V vary but they are very close and doesn't have any effect on signal reception.

Few points to remember:

• 3.3V transceivers consume less power than the 5V tranceivers. 
• Being interoperable with 5V transceivers is the biggest advantage 3.3V tranceivers have
• Most of the embedded products with micro controllers operate over 3.3V which is another added advantage for the 3.3V CAN Transceivers