Hello,

I have a beginner's question about CAN and level shifting and hope this is the proper place.

Using TJA1049 I am trying to talk to a device with CAN bus.
In the attached image yellow and red are the outputs of TJA1049 CANL and CANH.
Split pin of the part is attached to ground using a capacitor (per datasheet).

Signals in green and blue come from the device and
are in different voltage level (CANL goes negative).

Just joining the parts together (or using a bidirectional transistor level shifter)
did not help.

What would be the proper way to shift the output of TJA1049 from 0V..5V to -2.5V..2.5V?
Sorry, if this is something obvious..

Best regards.

 

CAN can cope with the common mode voltage being anywhere from -40V to +40V, so there is no need to level shift anything.

 

CANBus is a differential bus. At the idling or recessive state, both CANH and CANL sit at 2.5 volts. During the dominant state, CANH gets pulled to aprox 5 volts and CANL to aprox zero volts.But as Ian has mentioned, it can tolerate a lot of common mode voltage mismatch.
QUESTION FOR YOU: did you employ the 120 ohm termination resistor?

 

CAN can cope with the common mode voltage being anywhere from -40V to +40V, so there is no need to level shift anything.

Thanks @Ian0, @schmitt trigger for your responses and clarification. It seems I got further, messages from both ends get recognized (problem now is more on the other side of TJA1049 in serial part, a different topic).