Shielding of USB cable

Discussion in 'Wireless & RF Design' started by Peter Hanustiak, Jul 6, 2016.

  1. Peter Hanustiak

    Thread Starter New Member

    Apr 30, 2015
    2
    0
    Hi,

    I'd like to make USB - lightning cable that connects laptop with iPhone. I assume that when laptop is not connected to power supply then it is not grounded? Or is it grounded through chassis just by laying on the table?

    Which is the best option to shield such cable:
    A, shield connected to USB Ground wire through the whole length of the cable
    B, shield connected to USB Ground on both ends of the cable
    C, shield connected to USB Ground on single end of the cable (does it matter which end?)

    Which shield is enough for this application - braided, foil or both? thanks a lot
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,799
    A laptop is not grounded through the chassis by laying it on the table. Neither is your phone. The USB cable will make the laptop battery GND and the phone battery GND be at the same potential. In all cases the shield should be connected to one and only one ground. If the laptop is plugged into an AC adapter, then the shield should be connected to laptop GND. A phone's USB cable is normally connected as a charger in which case there should be no data on the USB cable to worry about.

    BTW -- what on Earth is a "lightning" cable? I've never seen that terminology before.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,570
    2,381
    You have to define GND as is usual here it is used for power common And earth ground.
    I assume you mean a lightening protection cable?
    If neither is connected to a wall socket or Modem, I would preferably keep them away from any earth ground conductor, in the event of a electrical storm.
    Max.
     
  4. Peter Hanustiak

    Thread Starter New Member

    Apr 30, 2015
    2
    0
    Thanks for prompt reply. By USB - lightning cable I meant cable with USB connector and lightning connector at the other end that is used in iPhones.

    So there are 2 wires used for charging the phone -> V+ and V- (which I incorrectly called USB Ground). V- is grounded when laptop is plugged into an AC adapter.

    There should also be a single shield around both of these wires. Is that correct? And my question is how should be this shield connected to V- wire (through entire length of the wire, at single end of the cable or at both ends of the wire)?
     
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