Part Number: ISO1050
I have recently had 3 units come across my desk which were described as 'not communicating on the CAN bus'.
These units are potted so I began by measuring R's & C's across CANHI, CANLO, GND and VCC against a reference unit. I immediately noticed that the resistance between the CAN lines and GND, and every permutation thereof, was reading below 100 ohm.
I then removed the potting to see what was causing this - I removed the input protection circuit and measured again, with the same result.
After replacing the ISO1050DUB package the unit functioned again.
I repeated this on the second unit, however this time it was just the CANHI and GND pair that exhibited a low resistance.
I verified that the power supply to each side of the transceiver was reading 5.05V and the CAN lines are protected by a dual CAN-BUS ESD protection diode and a common mode choke.
What could possibly be the cause of this and is there anything else we can incorporate into the design to prevent this from happening again?
All 3 units that have failed appear [ in removing the potting the markings were removed - but all the units were built at the same time, so components would have been off the same reel ] to be built from the same batch of ISO1050's so is it possible that this was a batch issue?
I have 2 extracted ISO1050DUB's if anyone would like to take a look also. I can extract the 3rd if necessary and try not to remove the package marking.
Thank you for using TI E2E.
Possible cause(s): Still early to say for sure, but one of the CAN pins may have been damaged due to an EOS event or during handling/processing. Admittedly it is hard to figure out which system EOS event may have caused this. This also depends on which ESD/TVS diode is chosen. We are not aware of any issues that might be caused or made worse by the potting process per se, but need to check. The curve trace data will help on this for sure.
Sorry for the broad list. Please feel free to let us know what you think and if it's possible to look into the above as time permits. We can also do a schematic review for you if you'd like - although that would be best done over email or private message(PM) to keep it off a public forum. We can then circle back and summarize the key points here later as needed.
We hope this helps.
In reply to Abhi Aarey:
In reply to Ryan Pannell:
Just summarizing the key points of our email discussion here:
1) Reviewed schematics offline 2) Choke looks OK.3) TVS can be optimized to reduce risk.
You are always welcome to contact us with any additional questions or comments.
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