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TS3USB221: Using a physical switch to switch between diff pairs and ensuring devices recognize the disconnection

asd asd
Prodigy 10 points
Part Number: TS3USB221

Tool/software:

I'm designing an FPGA development board around a SOM. The dev board will have an FT2232 that will be used for JTAG/UART Programming/Debugging.

I want to use 1 USB-C port for both programming/debugging and as a normal USB-C connection that goes to the USB Hub -> PHY -> FPGA.

I have two questions:

Can I use a physical switch on the Select input? The datasheet only mentions digital control.

Can I pull OE low permanently or do I risk one of the devices thinking that the connection to the TS3USB22 is a host when I switch to using the other device? I drafted the design below to generate a pulse on OE with an XOR Gate (SN74AHC1G86DRLR) whenever the physical switch changes, is this necessary/better (or works at all)?




  • 0
    TI__Mastermind 24440 points

    Hi

    1.Using a physical  switch to control the select pin of the multiplexer is fine.

    2.Pulling the OE pin low  permanently  is also fine in this application if the intended operation is to never fully disable this device.

    However there are some other things I would advise here based on your schematic.

    1.The VCC and GND pin of the device should be connected to their respective supply. (VCC connected to supply and GND connected to GND)

    2.In addition the 5V signal that will be placed on the TS3USB221 violates the recommended operating conditions  VIH spec of the device. Is there any way you can use the recommended VIH range with this device instead of 5V?

    Please let me know what you think and we can discuss this further

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    Prodigy 10 points

    Hello, 

    Thank you for reply,

    The image was illustrative; I have a more complete design now.

    Do you think this design would be better, or would it be no different than pulling OE low?

    Thanks in advance.


  • +1 in reply to asd asd
    TI__Mastermind 24440 points

    Hi,

    I'm not really a expert on the SN74AHC1G86DRLR device however   I would actually recommend pulling oe low if you always want the enable pin low.( This would have the D-,D+ always connected to either 1D+/- or 2D+/- paths)

    Based of your initial schematic it looks as if you want the enable pin low for your operation so using pulling down the OE should be fine and you wouldn't need the sn74ahc device.

    Please let me know if you need any additional assistance here and if I am misunderstanding something

    Regards,

    Kameron