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Original question:

ISO1050: Low resistance failure between CANHI, CANLO, GND

ISO1050: ISO1050's Differential input resistance change from 50K to 500KΩ

Eggsy Pang
Expert 4985 points
Part Number: ISO1050

Hi team,

My customers feedback that ISO1050 have some issue even though the chance of issue’s occurrence is small.

The issue is that sometimes ISO1050 can communicate successfully, sometime communicate unsuccessfully.

We test this chip which have issue and found  its input resistance between CANH and CANL is 500KΩ, while other chips' is 50KΩ.

I have below question. DO you have any suggestions? 

1. When IO1050's Differential input resistance change from 50K to 500KΩ, what happen will be?

2. What cause Differential input resistance change?

Thanks!

Below is SCH:

 

  • 0
    TI__Mastermind 49445 points

    Hi Eggsy,

    Thanks for reaching out to us with the customer issue.

    Before we provide our inputs, could you please help us with more information related to testing so that we better understand the issue? I would like to know how customer is testing the input impedance of CANH/CANL pins of ISO1050.

    1. Does he test on a PCB with all the components mounted (including terminator resistance) as shown in the schematic above?
    2. While testing for input impedance, do you know if other nodes are connected to the bus?
    3. While testing, do you know if TXD input is being driven? If the TXD is toggling or is it held at a single state?

    Please do help us with the above information, thanks,

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Expert 6195 points

    Hi Eggsy, 

    We haven't heard from you in a few days. Were you able to determine what caused the change in impedance? 

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    TI__Expert 6195 points

    Hi Eggsy, 

    We haven't heard from you in about a week, so I'm going to assume that you were able to determine what caused the change in impedance. If this is not true, please feel free to respond to this post or start a new one and we would be happy to assist you. 

    Best regards, 

    Dan