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ISO1050: ISO1050 application

Nanfang Liao
Intellectual 2085 points
Part Number: ISO1050

Hello Team,

My customer uses ISO1050, the schematic is as below.

They test the waveform of CAN differential signal(pin7 and pin8) and TXD(pin3).  The yellow is CAN differential signal, there is ringing on signal edge, but the TXD waveform(red) is very good, and the CAN communication is also OK. Please help to check if the CAN differential signal is OK? thanks

Regards,

Nanfang

  • 0
    TI__Intellectual 2855 points
    Hi Nanfang,

    Few questions to understand the system better,
    1) Was 121ohm and both 4.75k Resistors populated?
    2) what is LB in the schematic?
    3) what is on the other side of bus?
    4) How was differential signal measured? using differential probe? two single ended probe?

    Regards
    Tejas
  • 0 in reply to Tejas Hommaradi
    TI__Intellectual 2085 points

    Hello Tejas,

    See my inputs as below, please help to give your comment, thanks

    1. Only 4.75k resistors are populated

    2. LB is ferrite bead

    3. Below is other side of bus schematic

    4. Yes, they used differential probe

    Regards,

    Nanfang

  • 0 in reply to Nanfang Liao
    TI__Intellectual 2855 points

    Hi Nanfang,

    Ringing is generally due to reflections of communication wave, usually this occurs due to impedance mismatch in a network at  signal transition. The impedance mismatch mainly occurs at non-terminated nodes and also due to type of cable used. Until the ringing converges quickly there will be no data errors, only if actual system has very long cable or very high data rate then ringing may cause data errors. 

    Usually each cable end is terminated with a termination resistor to eliminate line reflections. The termination resistor value matches the characteristic impedance of the cable which is 120 Ω for standard cable. can you please check how customer arrived at 4.75k ohm. can they try measuring with 120 ohm instead?

    Can you please check on the amplitude (voltage) of differential signal as it was not that clear from waveform, also please check on the cable length, number of nodes and max data rate used in the system.

    Regards

    Tejas