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  • USB front end components

    Hi to everyone,
    this is my first time to design a USB for a portable device, i mean the client and not the host.
    My application is mainly intended for battery recharge from USB power port and slow USB data stream for firmware upgrade.
    The main key is to protect the data lines and power lines in order to get a device very strong, because it will work in harsh enviroment (outdoor and so on)
    The entire board dimension is small, 26 x 49 mm.
    This is what i've designed, but i'm not sure about both TVS for data lines and power line.
    Also TL1 have a break down voltage from 6.4 to 7v and it's really close to maximum rating of U1.
    Anyone have some suggestion about this topic? Better components?
    Any comments are welcome.
    Thanks in advance, Luca
    Attached Files

  • #2
    If this is a device, I am not sure about the fuse. The fuse should be on the source side, if you have it on device site too, you may get additional voltage drop across the fuse. Be sure you can replace it by 0R if needed.

    About the exact values and part numbers of ESD and Over voltage protection - often I use components recommended in reference schematic. Possibly I have a look at the protection manufacturer website and check their recommended components for specific applications and environment .. maybe like this (the file is also attached): http://m.littelfuse.com/~/media/elec..._guide.pdf.pdf
    Attached Files

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    • #3
      Good evening Robert,
      I can replace that PTC with 0R 0805 resistor if i have trouble in the application.
      I'm not sure too but i need to protect against short circuit fail or wrong power supply connection.
      I've asked to Microchip about OVP for that IC battery charger but they say only "do not violate the max rating" ... and we know, this is a too generic expression
      For the choice i've used exactly the PDF from Littlefuse that you have posted above, i need 30kV! But i've never used before the SP0502B.
      I'm trying to design in the best way in order to leave open different ways to make and pass all the test.
      Actually i'm planning to design the whole PCB board only with TH and with clearance and components placement/choose for the lowest cost and time
      for PCB production and assembly.
      Anyway thanks a lot!


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      • #4
        Just a note: TH may be more expensive than SMT - depends on quantity.

        Also, when I am using standard connectors (such USB), and I am designing a device (the board which is going to be powered from PC USB or USB charger ), normally we only add necessary protection. If you are using standardized power supply with specified connector (e.g. USB) - that power supply should meet voltage specification and connector will protect from things like reverse voltage. If we are not sure what power supply is going to be connected, then we add a lot of protection.

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        • #5
          Good evening Robert, thanks for reply!
          Infact i'm not sure which kind of power supply will be used, and also of which "quality" they are... i've seen a lot of time a "poor quality" USB charger that present a lot of noise and ripple at output voltage and somenthing they do "strange" things...
          Sorry for my bad typing, with TH i mean Through Hole, so no blind vias
          I'm not referring to THT components.
          By the way i'm looking for the best Fedevel Accademy Courses for me for the Christmas Holidays

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          • #6
            I agree about USB chargers - they are various qualities.

            Ah, I thought that you mean TH components Yes, you are right. Through hole VIAs only are much cheaper than a PCB with uVIAs.

            PS: Thank you very much for signing up and supporting us this way

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            • #7
              Yes i'm still developing this board, finished the schematics and im doing the layout thinking about the manufactoring cost and assembly.
              I've also right now payed the Advanced PCB Course from your Accademy

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              • #8
                Thank you very much
                Luca

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                • #9
                  Thanks to you
                  robertferanec
                  Administrator
                  robertferanec!
                  I've already watched lesson 7 and i'm really happy about this course!
                  I don't have time now for do practice so I'm just watching the video and listen very carefully, but i'll do it!
                  By the way the attached image you can see the board that i've sayed before, the digital section, routed on 4 layers PCB without uVias!
                  Could you spot some "weak point" by your great experience?
                  I'm trying to keep the cost of board, components, PCB fabbrication and assembly as low as possible, so this means the easyest as possible.

                  Comment


                  • #10
                    Nice board
                    Luca

                    PS: Just looking at the 3D model I do not see anything unusual

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                    • #11
                      Good morning
                      robertferanec
                      Administrator
                      robertferanec and thanks for reply!
                      I'm trying to do my best and can you evaluate within more in detail this design?
                      If, yes, which information do you need?
                      Maybe the entire Altium Project? I mean schematics and PCB files?

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                      • #12
                        Luca it is always very hard for me to tell people that I do not review designs. I am sure you understand
                        However, if you have any specific questions, you can always ask here - if I can, I will help.

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                        • #13
                          I can understand
                          robertferanec
                          Administrator
                          robertferanec, it's ok
                          As you know i came from some experience about RF and SMPS design and layout, also of other type of board... and I also have some years of experience in an assembly house, especially in stencil treatment and Pick and Place machine but.. i'm glad to say that i really like the course and i'm planning to download it asap to do some practice with a project that you have also worked.
                          I've a question about Pick and Place file generating but I don't know if here is too much "off topic" or is still ok.

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                          • #14
                            You can ask about pick and place here, no problem.

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                            • #15
                              There is a way for configure the output column in order to customize/clarify the file?
                              For example, in Altium reports by default both the coordinates X,Y for the center of components and the pin 1.
                              It's possible to disable the coordinates for pin 1?
                              Again, it express with "m" letter the unit, but i don't want to see it at the file, is possible to disable?
                              This is only an example, my question is in general as the first line.

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