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ISO1050: Shorted output on ISO1050DW

Prodigy 60 points

Replies: 12

Views: 252

Part Number: ISO1050

Hello,

We use ISO1050DW transceivers on out PCBs for CAN communication. I wanted some insight on what would have to happen internally on the IC for the CANH/CANL pins to get shorted to GND pin on the transceiver IC. Also, we took the transceiver ICs off of the board to inspect which GND pin was getting shorted to the CANH/CANL pins on the IC, we found that pin10 was the one getting shorted with CANH/CANL on the transceiver.

We have 15 nodes on our CAN network and each node uses a ISO1050DW transceiver for CAN communication. Recently, we have seen that the CANH and/or CANL pins on the transceivers on some of the nodes get shorted to the ground pin on the transceiver after continuous operation for a few hours bringing the whole communication network down. On some transceivers, it is not necessarily shorted, but the resistance is very low. On a good transceiver, we see a resistance of around 7 Mega Ohms. On the faulty transceivers we see resistances in Kilo Ohm range or shorts (very low resistance like 10-100 Ohms). We tried to understand reasons as to why this would happen. The working temperature of each node never goes outside the recommended temperature range for ISO1050DW. We don't see this problem on a huge number of transceivers, but we are seeing it more than we would like to.

  • Abhijit Bidwe1,

    I'm sorry to hear you are experiencing some failures in your CAN network. Having the CAN/CANL lines shorted to ground might be because of a transient overvoltage event over the bus. Are ay TVS diodes being used for bus protection? If so, can you share the TVS diode part number so that I may check to make sure it is effective? Could you also share a schematic of the CAN transceiver in this system along with any components (TVS, termination, choke, etc) on the bus?

    Respectfully,

    Lucas Schulte

  • In reply to Lucas Schulte9:

    Hi Lucas,

    Thanks for getting back. We do have an ESD protection diode. The part number for that is NUP2105. I have attached a screenshot of the transceiver schematic. 

    Let me know if you have any questions. 

  • In reply to Abhijit Bidwe1:

    Abhijit,

    It looks like the TVS diode being used has a clamping voltage above the absolute max voltage tolerance of the ISO1050 CANH and CANL. This means that voltage could happen on the bus that damages the ISO1050 and the TVS diode wouldn't protect it.

    Below is a link to a document that explains how to properly protect the ISO1050 as well as the ISO1042. Also, the ISO1042 and ISO1044 are our newer CAN transceivers will several improvements made over the ISO1050. 

    Respectfully,

    Lucas 

  • In reply to Lucas Schulte9:

    Hi Lucas, 

    Thanks for sending the application note. We changed the TVS diode to the one that is specified in the application document (CPDT-12V) and I have attached a screenshot of the results we got when we scoped the pins of the ISO1050 IC. 

    The blue line is VCC2 (pin 16), the green and the yellow are the CANH and CANL (pin 13 and pin 12) respectively, the red is 12V supply that is converted to 5V (which is applied at VCC2) via a regulator. 

    We still see transients on the CAN lines after the change of diode. Can you help with this?

    Thanks,

    Abhijit

  • In reply to Abhijit Bidwe1:

    Abhijit,

    Unfortunately it doesn't appear that the image came through. Can you try again? Seeing these waveforms will be very crucial for root cause analysis. 

    Respectfully,

    Lucas

  • In reply to Lucas Schulte9:

    Hi Lucas, 

    Thanks for sending the application note. We changed the TVS diode to the one that is specified in the application document (CPDT-12V) and I have attached a screenshot of the results we got when we scoped the pins of the ISO1050 IC. 

    The blue line is VCC2 (pin 16), the green and the yellow are the CANH and CANL (pin 13 and pin 12) respectively, the red is 12V supply that is converted to 5V (which is applied at VCC2) via a regulator. 

    We still see transients on the CAN lines after the change of diode. Can you help with this?

    Thanks,

    Abhijit

  • In reply to Lucas Schulte9:

    Lucas,

    Here is the screenshot. 

    The blue line is VCC2 (pin 16), the green and the yellow are the CANH and CANL (pin 13 and pin 12) respectively, the red is 12V supply that is converted to 5V (which is applied at VCC2) via a regulator. 

    Thanks,

    Abhijit

  • In reply to Abhijit Bidwe1:

    Abhijit,

    Unfortunately the time scale of the waveforms is much too large to see meaningful switching patterns and transients. Can you provide waveforms in a simillar timescale as the example below? Ideally catching the non ideal transients and behaviors in question.

    Respectfully,

    Lucas

  • In reply to Lucas Schulte9:

    Abhijit,

    Getting waveforms zoomed in on the noise will help eliminate the possibility of these transients just simply being artifacts by the measurement system you are using. Also note that the TVS diode won't eliminate transients but reduce them to Vclamp or below. 

    I am marking this thread as resolved for but please feel free to make a new related thread if you need to continue the conversation.

    Respectfully,

    Lucas

  • In reply to Lucas Schulte9:

    Hi Lucas,

    I hope this will give you a better representation.