capacitor value for VUSB


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  1. #1
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    Default capacitor value for VUSB

    Hi,

    I have a program that works on a development board but does not work on the board I made. The 18F4550 works for the internal program but the USB portion does not work at all. I have checked the traces and verified everything is OK. I am confused about the VUSB pin and what capacitor values go on that pin. I change that value and the computer starts to recognize it but I can't find the correct value. Can anyone help me?

    Thanks,

    Chris

  2. #2
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    Default

    Nobody ever reads Datasheets... Section 17.2.2.8

  3. #3
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    Default

    The only problem is I have seen many different configurations of caps... For example, .470uF, .200nF, .47uF and the data sheet for the 18F4550 which is 220nF. Since I have tried them all, maybe there is a different problem I am not seeing.

  4. #4
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    Default Re: capacitor value for VUSB

    I know this is an old thread, but it's still a good place to keep this subject.

    The datasheet for the 18F4550 says 220nF, but all the schematics I see use 470nF.

    Is there a reason why a lot of people use double the rating?

    Robert

  5. #5
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    Default Re: capacitor value for VUSB

    Hi Robert,

    The data sheet (page 383) says that 220 is the minimum, but 470 is "typical" or recommended. Max is 12 uF, so you have some range. Usually manufacturers don't put on the bare minimum.
    http://www.scalerobotics.com

  6. #6
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    Default Re: capacitor value for VUSB

    Thanks!

    I finally found the exact values in the DC Characteristics on page 385 table 28-5 (in my version), the 220nF I found earlier was from within the USB section.

    It's comforting to find something more detailed. At least now I know why everyone is using the "typical" 470 when the section I was reading said only 220. I wanted to order caps but wanted to know exactly where I was going first.

    Robert

  7. #7
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    Default Re: capacitor value for VUSB

    Quote Originally Posted by Demon View Post
    I finally found the exact values in the DC Characteristics on page 385 table 28-5 (in my version)
    which is page 383 as printed on the page, but 385 on the adobe index. Would be nice if the two matched!
    http://www.scalerobotics.com

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