TCAN4550: TCAN4550 unterminated drop-lines (stubs) connected to bus

Jeff Xie

Part Number: TCAN4550

Hi team,

We have three nodes connected in line. The each length is 10M. The resistor is terminated on board. Customer may unplug the wire from the node 3, which cause node 1 and 2 can not work.

How to solve this problem? Thanks

over 5 years ago

0 Max Robertson over 5 years ago

TI__Guru 62910 points

Hi Jeff,

Is termination present on all three nodes, or on just one or two nodes? When node 3 is removed, is the bus still terminated? (If so, via what resistance value?) Have you tried observing the CANH and CANL signals on an oscilloscope to verify the signal quality?

Regards,
Max

0 Jeff Xie over 5 years ago in reply to Max Robertson

TI__Intellectual 1780 points

Hi Max,

Is termination present on all three nodes, or on just one or two nodes?

On all three nodes.

When node 3 is removed, is the bus still terminated?

No, the cable is still connected to network.

Have you tried observing the CANH and CANL signals on an oscilloscope to verify the signal quality?

No, please let me if you need it.

0 Max Robertson over 5 years ago in reply to Jeff Xie

TI__Guru 62910 points

Hi Jeff,

Yes, observing the waveforms during a normal and failing case would be very useful in understanding the root cause of the issue.

From what you've described, though, it sounds like the issue may be related to operating the bus without termination when node 3 is disconnected. CAN buses require some termination resistance between CANH and CANL in order to properly switch between dominant and recessive states. You can read more about the importance of termination in this blog:

e2e.ti.com/.../the-importance-of-termination-networks-in-can-transceivers

Regards,
Max

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TCAN4550: TCAN4550 unterminated drop-lines (stubs) connected to bus