3.3V and 5V CAN Bus Transceivers

Hi Sam,

5V CAN and 3P3V CAN nodes can be mixed as the bus voltage requirements are the same. For instance, in both 5V and 3P3V CAN parts a dominant on the bus is represented by a differential voltage greater that 900mV and a recessive is represented by a voltage less than 500mV.

The problem with mixing 3P3V and 5V comes on the interface between the host controller and the transceiver. From the host controller output to the TXD of the CAN part you will be OK as the CAN input excepts TTL levels and the TXD pin most likely 5V tolerant on the 3P3V parts. Going the other way though usually causes the problem as a 5V transceiver is going to swing full rail (0-5V) and a 3P3V controller will not be able to handle this and may cause damage to the part. For this though there is a solution that exists. Some 5V CAN transceivers have a pin, VIO or VRXD, that allows the user to set the output level threshold by tying it to a voltage source.his allows you to set the RXD output to 3P3V rather than 5V to obtain interoperability in a 3P3V system. The SN65HVD257 is a 5V CAN transceiver from TI that offers this feature.

Please let me know if you have any more questions and I will be glad to help.