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Usb2.0 impedance calculation

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  • Usb2.0 impedance calculation

    How to calculate impedance for usb2.0 in pcb and can we connect usb shield with gnd through ferrite.

  • #2
    USB 2.0 impedance is usually 90 ohms (45 single ended). Here is a document which you can find useful:

    Click image for larger version

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    To get these impedance, the best is to check with your PCB manufacturer. You can approximately calculate track width and space for your PCB (e.g. use Saturn PCB Toolkit - free software), but you will never calculate the same number as your PCB manufacturer will need to use:

    I would not connect usb shield through ferrite:


    • #3
      So, finally which one I prefer for the calculation...Saturn r else my pcb manufacturers


      • #4
        You have more options:
        - The simplest is to use your PCB manufacturer's online calculator (often they have some - you select the stackup you would like to use and you can calculate the impedance and track geometry there) e.g. something like this
        - or ask your PCB manufacturer to send you their standard stackup, impedances and all dimensions (you need to have direct contact in your PCB factory)
        - or you can try to design your own stackup, approximately calculate the numbers in Saturn and then ask PCB manufacturer to confirm or adjust these numbers (not easy to do, can be expensive and can take a lot of time)

        In your PCB, use the numbers from PCB manufacturer.