Strange CAN BUS waveforms when using the PCAN optoadapter

[Nick_Adams]

Hi all,

I have 3 devices in a CAN bus system.
1st device is isolated from the others by using the PCAN optoadapter.
CAN BUS data rate is 250kB/sec
1st sends 4 TPDOS at 100ms.
2nd device sends 1 TPDO at 10ms
3rd device sends 4 TPDOs at 100ms.
Cable length 2-3meters.

System.png (18.65 KiB) Viewed 55700 times

The 1st device distorts the bus as the following figure shows:

CANH_CANL

12.PNG (408.48 KiB) Viewed 55700 times

When I reduce the 1st device TPDOS to 2, then there is no issue on the bus.
Unfortunately I do not have access before the isolation but only after were all devices are connected.

Do you have any hint why this is happening?

Thank you
Nick

[M.Heidemann]

Hello,

Please check the termination on your system in an unpowered state, make sure
you have around 60 Ohms between CAN-High and CAN-Low on both sides.

It could be possible that you need additional termination on your primary side.


Please report back to us with your findings.

Best Regards

Marvin.

[Nick_Adams]

Hi Marvin,

Eventually I was able to replicate the fault that the customer sees in the lab.

The issue is time related because the power supply of the PCAN opto-adapter goes lower than the PCAN opto-adapter threshold and this makes it to complain.

When I reduce the TPDOs then the needed power is lower and the issue goes away.

I will upload some more photos tomorrow.

Thank you
Nick

[M.Heidemann]

Hello Nick,

Please make sure the PCAN-Optoadaptor is properly supplied with the needed voltage throughout your tests.

Furthermore, did you manage to obtain the aforementioned pictures?

Best Regards

marvin