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  • USB Freeze random

    Hello everyone,

    I am facing a problem in my PCB :

    There is a Module SIM7600 connected to the processor SAMA5D27 through USB interface. When we try to make calls, there is no problem ; the call connects perfectly and the data flow is fluid. We thought the product is good and works perfectly, but after a while may be 10 hours later, the SIM7600 is connected to the SAMA5D27 processor (Considering the fact that the Module SIM7600 is still ON and connected to the Network).

    What we observe is, the processor is not able to communicate to the Module through USB bus interface which was functional few hours before, the AT commands does not pass through and there is no activity in the USB bus lines.

    We could have narrowed down the source of the problem if the problem exists on all the PCBs but in a lot of 30 PCBs only 6 is producing this bizarre problem.

    Could it be related to USB routing ? Anyone faced this situation before ? Please help me out guys.

    Regards,
    Naveen

  • #2
    With modems, many problems are around power and decoupling. Modems can change power in spikes (depends how strong signal they have) and that can sometimes freeze or discontent USB. Maybe it could be also problem in this case?

    PS: I remember playing with one board - we created an aluminium box which was grounded, placed board inside and by covering and uncovering we tried to play with wireless power of the modem ... but I do not really remember if that helped

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    • #3
      Hello RObert Feranec,
      Thanks for your reply.

      When the Modem is in full load (when it tries to connect to network or make call connection) the module does not turn off, it works without any problem. Can I infer that there is no problem with the Power Supply ?

      The problem of USB freeze happens completely at a random time. Infact there is no parallel process running when there the USB freeze happens.

      Regards,
      Naveen

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      • #4
        is the physical connection stable? i had a craked solder joint in one of the data pins of a usb connector once..

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        • #5
          Thanks for your reply Paul. I will check on that !

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          • #6
            When the Modem is in full load (when it tries to connect to network or make call connection) the module does not turn off, it works without any problem.
            - passing the initial connection is not a good stability indicator (there still could be a problem with power). Many random problems and freezes are caused by power drop in completely random times and it is not easy to replicate them.

            Maybe try to add some big capacitors (e.g. 330uF caps) and more smaller caps around the modem (10uf, 100nF) and see if that helps. Possibly, tune out the power voltage close to the top of the maximum power voltage of the module and see if that helps to improve the situation. I am not saying that the problem is power ... but who knows, could be.

            How many capacitors do you use? Especially have a look at this comment:

            Note: If the power supply for VBAT pins can support up to 2A, more than 300uF capacitors are recommended .Otherwise users must use a total of 1000uF capacitors typically, in order to avoid of the voltage drop more than 300mV.

            I found it here: http://www.mt-system.ru/sites/defaul...sign_v1.02.pdf

            Click image for larger version

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