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Thread: USB Host 5V in/out

  1. #1
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    USB Host 5V in/out

    I'm wondering if I can connect a self powered USB device to the USB Host connector without cutting / resoldering the trace at the H/D pads. I.e. I'd like to connect host powered devices (mice...) and self powered devices (e.g a touch screen) without soldering when I change the device. I assume that the TPD3S014 will block incoming USB voltage but I'm not really sure.

  2. #2
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    Nobody with experience using bus powered and selfpowered USB devices with the T3.6 USB-Host?

  3. #3
    Senior Member+ defragster's Avatar
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    Only anecdotal ideas … I've connected powered USB Hub to T_3.6 ( and T4 beta ) without trouble. It doesn't push power to Host Teensy - just devices it connects. Assuming the same for any self powered device.

    Wouldn't that just be like Putting a Teeny on with VIN<>VUSB trace cut and externally powered? This powered device just shares GND and data on the +/- pins. I did that with Teensy to PC where Teensy was running display and externally powered - only thing that fed back to PC was 1 AMP through GND because I didn't have good GND on the matrix (32x32 RGB) to the power source it had - added GND fixed that and then Teensy was better to program from PC.

  4. #4
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    It doesn't push power to Host
    That might be true indeed. For some reason I thought that a self-powered device will put 5V on the USB like a USB host does... On the other hand: why did Paul add those Host/Device pads on the board?

    Wouldn't that just be like Putting a Teeny on with VIN<>VUSB trace cut and externally powered?
    I want to avoid cutting the "Host trace" and solder the "Device pad" since then host powered devices would not work anymore.

  5. #5
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    Thanks defragster, with that obvious push in the right direction it was easy to google:

    .. No USB device, whether bus powered or self powered can drive the VBUS on its upstream facing port. If VBUS is lost, the device has a lengthy 10 seconds to remove power from the D+/D- pull-up resistors used for speed identification...
    So, seems to be save to connect a self powered device to the USB Host. So, I'll give it a try and see if something starts smoking :-)

  6. #6
    Senior Member+ defragster's Avatar
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    Cool - good to know my assumption/anecdote was properly enforced as a rule.

  7. #7
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    I am trying to get 5v out on the USB host pins. At the moment I am only powering it via the USB input. I am not getting 5v out. I do have the pins turned on. Is there a threshold voltage it must reach before the USB Host out will work or do I have to feed it through the VIN

  8. #8
    Senior Member+ defragster's Avatar
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    In my use the 5V from USBHot is there with only the software stack activated in the example sketches I've run. The 5V is wired and perhaps switched as needed across the PCB to the Host pin, no added wires or connects except from those header pins.

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