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ISO1050: Ringing in the falling edge

Lacey Lin
Intellectual 2900 points
Part Number: ISO1050

Hi team,

My customer use the ISO1050 to isolate the can node and can bus.

below is the schematic:

But they find the ringing in the falling edge, as below:

The purple is CANH, green is CANL, orange one is CANH-CANL, yellow one is RX.

After they short the Ferrite bead, the ringing issue has improve. See below:

The inductor value of the Ferrite bead is about 0.8uH

Can you help to comment if the ringing is caused by the Ferrite bead?

Please help to analyze the solution to fixe the ringing of the signal.

Lacey

Thanks a lot!

  • 0
    TI__Intellectual 2325 points
    Hi Lacey,

    Thanks for using our E2E forum and for sharing some schematics and waveforms in the first post itself - it helps :)!

    Yes, it looks like the bead is causing this. Generally when we have switching activity [rising and falling edges] with an inductive component, we see voltage ringing. the fact that you don't see it in the second scope shot essentially confirms this.
    the inductive component can be in the form of a bead, common-mode choke or long traces/cables.

    What data rate is the customer running at ? From the second shot , it appears to be 125kbps - not sure if this is the actual data rate or just for debug- can you please confirm? [8 * 1us = 8us; 1/8us = 125kbps] If so, then as long as the ringing subsides quickly, then the MCU as well as the other nodes should still be able to communicate without errors because usually the sampling point is at 80% of the bit duration, and by that time the ringing would have also died down and won't affect communication.

    Any more details on this? Is the customer experiencing comms failure?
    Some general notes on the schematic, C14 and C15 are unusually large [nF], and it can load down the nodes. Usually 100pF caps are more common. Sometimes, these large caps can also interact with the inductance of the beads and also with the capacitance of the TVS [diodes], to form an RLC network which can affect the transient response.

    Regards,
    abhi
  • 0 in reply to Abhi Aarey
    TI__Intellectual 2325 points
    Lacey,

    Just wanted to check if everything was okay here?

    Please let me know if this addressed your concerns or if you have more questions.
    Any further details as mentioned in my previous post would also be helpful.

    Thanks,
    Abhi
  • 0 in reply to Abhi Aarey
    TI__Intellectual 2325 points
    Lacey,

    It's been a while since we heard back from you. I am going to retire this thread - please feel free to reach out back to us if you have any further questions.

    Thanks,
    Abhi