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ISO1042-Q1: Measurement of input capacitance (CANH/CANL)

Jeffrey Chung1
Expert 2490 points
Part Number: ISO1042-Q1

Dears,

I'd like to ask you on measurement of input capacitance (CANH/CANL) that says in datasheet page 10 of ISO0142-Q1. Please let me know how to measure this input capacitance of datasheet, and share the related document with me. I think that measurement method of datasheet is different from my customer's measurement method. Please refer to the attached file below. Could you explain on the difference of both?

Measurement of input capacitance.pdf

Regards, Jeffrey

  • 0
    TI__Expert 6955 points

    Jeffrey,

    https://e2e.ti.com/support/isolation/f/1013/t/919110

    This is another thread with a similar question that has been answered. It is advised to measure the capacitance in the device's operational state and with a frequency greater than 5kHz. CAN bus communication will be much higher than this so it is advised to measure at around 1MHz.

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    Expert 2490 points

    Hi Lucas,

    Thanks for your support. I saw an another e2e thread that you told me on previous post. It will help me and my customer understand the biasing network of CAN transceiver. I will ask you some questions if I have some issues.

    Regards, Jeffrey

  • 0 in reply to Jeffrey Chung1
    TI__Expert 6955 points

    Jeffrey,

    I am marking this as resolved for now but please feel free to ask questions if you need further assistance. 

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    Expert 2490 points

    Hi Lucas,

    I need to ask you some more questions. My customer is testing the internal capacitance of CANH, CANL, and short to CANH & CANL through LCR meters under condition of VCC2(Pin 8) = 5V, CANH(Pin 7) or CANL(Pin 6) or CANH(Pin 7) & CANL(Pin 6) = connect to LCR meters, and GND2(Pin 5) = connect to LCR meters. Test results are as follows. CANH(Pin 7) only is 44.99pF, CANL(Pin 6) only is 42.77pF, and CANH(Pin 7) & CANL(Pin 6) is 87.63pF. Is there any problem? or Measurement method through LCR meters is correct?

    Also, I want to know the device's operational state that you told me on previous post. Please let me know the details.

    Regards, Jeffrey

  • 0 in reply to Jeffrey Chung1
    TI__Expert 6955 points

    Jeffrey,

    What frequency is the LCR using to make measurements? To replicate typical operating conditions, the frequency should be around 1MHz.

    The device's typical operational state would be powered on and transmitting between 1Mbps and 5Mbps. Since capacitance is a function of frequency, it then makes sense to take measurements at 1MHz since that would be within the typical range of communication speed in most applications. 

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    Expert 2490 points

    Hi Lucas,

    The frequency of LCR meter is 1kHz. They will test the capacitance as a changed frequency.

    Also, It says that ISO1042-Q1 meets the ISO 11898-2:2016 physical layer standard in datasheet. Is there any test result document or related document? Please share it with me.

    Regards, Jeffrey

  • 0 in reply to Jeffrey Chung1
    TI__Expert 6955 points

    Jeffrey,

    Yes please have the customer test with 1MHz instead of 1kHz.

    I will respond about the ISO  standard on Monday after I discuss this with my team.

    Respectfully,

    Lucas 

  • 0 in reply to Lucas Schulte9
    TI__Expert 6955 points

    Jeffrey,

    I have information on the ISO 11898-2:2016 test standard for the ISO1042-Q1 but I can't share it on the forum. I can email it to you if you accept my friend request. 

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    Expert 2490 points

    Hi Lucas,

    Thanks for your support. I have already accepted your friend request. So you can email me it. I'll waiting for your email.

    Regards, Jeffrey

  • 0 in reply to Jeffrey Chung1
    TI__Expert 6955 points

    Jeffrey,

    The information has been sent over email and we discuss the issue further if needed also over email. 

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    Expert 2490 points

    Hi Lucas,

    Thanks for your support. I'd like to ask you the reason why the internal capacitance test had been deleted in ISO11898-2: 2016 version. My customer already asked it to ISO.org but there was no answer. Please share it with me if you know this revision history, or if you have a related document and comment. This design will be lost unless my customer provides some requirements to their automotive end customer.

    Regards,

  • 0 in reply to Jeffrey Chung1
    TI__Mastermind 49835 points

    Hi Jeffrey,

    It is a holiday today in the US and hence, Lucas is away from office.
    I do not know why the internal capacitance test method has been removed from the ISO 11898-2:2016 version. I will check back with my colleagues tomorrow once they are back to office and will respond to you latest by Wednesday, thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Expert 2490 points

    Hi Koteshwar,

    Thanks for your kind reply. I'm waiting for your response. I hope that it will be help me to resolve this issue.

    Regards,

  • 0 in reply to Jeffrey Chung1
    TI__Mastermind 49835 points

    Hi Jeffrey,

    After having spoken to my colleagues, I can confirm that we do not know the actual reason for removal of the internal capacitance measurement test.

    We believe that this could be something that is more properly defined at the module level rather than for the physical layer, and it might have already been covered by different implementation standards (like J2284, etc.).  The test also didn’t seem to account for the input resistance of the CAN receiver which, if comparable to the series test resistance, could result in measurement error.

    Apart from the above points, we do not have any other speculations to make. Thanks.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Expert 2490 points

    Hi Koteshwar,

    Thanks for your support. I appreciate your response, even though I expected that like your answer.

    Regards,