CAN termination vs. choke

At a guess, the choke is there to suppress EMI from the board from leaking out along the CAN lines, rather than as a component of the CANbus termination as such.

Yes, of course. The terminator is on the transceiver side, then the choke, then connection to CAN lines.

If the terminator would be on the line side, the common mode choke would not work.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Sorry, I am missing something here.

The choke on the CAN bus side, before the terminator, means the impedance seen on the CAN bus does not match the required 120 ohm (except at DC), no ?

Can you explain your point Vladimir ?

Thanks, Best Regards, Dave

then connection to CAN lines.

work.

It is a COMMON MODE choke.

Sure. I'l send you a bill.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

It's a common mode choke, meaning that it's bifilar wound (or should be), to allow differential currents to pass without being molested, but to block common-mode currents.

At 51uH it has an impedance of 100 ohms at 300kHz or so -- if the CAN bus is operating at significantly slower than that, the inductance wouldn't matter even if it weren't a common-mode choke.

Thanks Tim. This choke is actually sector-wound, not bifilar, so has a very high Lstray (either

Looks like it was placed here out of concern for the ~3v pp common-mode noise on the CAN bus... Still digging...