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RXD pin of ISO1050 goes low for 20uS

Rohit Garg
Prodigy 20 points
Other Parts Discussed in Thread: ISO1050

I am using an ISO1050 for CAN bus. I found some Stuff error when CAN running. when we done troubleshooting we found that its RX pin goes low for some time (variable time 10Us~20uS). for this test we shorted pin 1,8 and  pin 4,5 and give 5V from an external power supply. we disconnect the trans-receiver from microcontroller so that it can not receive any data. we put 60 Ohm termination on CANH and CANL pin and TXD pin is pulledup using 1K resistor.

Plz suggest wat could pull that pin to low, when both input and output of that pin is not connected.

Thanks & regards

Rohit Garg

  • 0
    TI__Guru 55795 points

    Hi Rohit,


    I am assuming you are using 8-pin SOP package of ISO1050. Did this happen just once or does it repeat? When does RX pin go LOW or does it happen at random instances? Could you please share the schematic and screenshot of the error that you have seen (CANH, CANL, RX)?

    Did you try testing another sample of ISO1050? Does it happen only on one sample or does it repeat on all the samples you have tested?

    Best Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Hi..

    Thanks for replying.

    We are using DUB package of ISO1050. this phenomena is repetable, as per our understanding this IC is pickup some ground noise as this IC and controller ground is  same. for this we install a Common mode chock in CANL and CANH path, errors reduced but didnt eliminate.

    we put commond mode in our power supply path, but error increased. so plz suggest how to reduce that ground pickup??

    Thanks

    Rohit

  • 0 in reply to Rohit Garg
    TI__Guru 55795 points

    Hi Rohith,

    Thank you for letting us know about the experiments you have conducted. It would help us understand the problem better if you could share us the schematic.

    Please add the below circuitry for filtering common-mode and differential noise.

    1. Please also add differential filter on CANH and CANL lines. 10Ω resistor and 330pF capacitor, the capacitor is connected from CANH/CANL to GND and the resistor is in series connecting CANH/CANL lines to termination resistor.

    2. In addition, terminate the node with common-mode filter as shown in the below picture (in place of a single 60Ω termination resistor).


    Best Regards,
    Koteshwar Rao