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MUX509: RS232 and USB2.0 compatible MUX

Jackson Thomas
Genius 14375 points
Part Number: MUX509
Other Parts Discussed in Thread: CD4053B, MUX36D04,

Hi,

I am trying to design a system to MUX between two RS232 lines and two USB2.0 lines.  I am trying to find a MUX that can support the bipolar +/-12V of the RS232 while also having the bandwidth for USB.  The MUX50x series all say they have 500MHz bandwidth which should theoretically be enough for 480MHz USB, but have you seen anyone try this with any TI MUXes?  It doesn't appear that any of the USB interface MUXes support these voltages so I'm looking more general purpose.  Any info you could provide would be greatly appreciated.

Thanks,

Jackson

  • 0
    TI__Expert 3900 points
    Hi Jackson,

    This ability to support that voltage range at such a high BW is not a common request. We definitely have devices that can support either the desired voltage range OR the USB BW but not both. Like you mentioned, the USB 480Mbps is typically clocked on both the rising and falling edge putting the fundamental frequency at 240MHz. If you are very careful and good at system design you can potentially accomplish the goal with a switch where the BW is 2x your fundamental frequency (480MHz). But a good rule of thumb is to design for BW = 3x fundamental frequency.

    Is there a way to acomplish this task by multiplexing the USB2.0 lines separately from the RS232 lines?
  • 0 in reply to Dakotah
    TI__Genius 14375 points

    Dakotah,

    Thanks for the quick response.  I figured it would be tough to find a single MUX that would be applicable.  While I would like to keep the USB lines and RS232 lines together for simplicity, its looking like I might have to change to two different MUXes.  I will have extra pins that I can route the high voltage lines through and keep the USB lines alone, though this might get cumbersome.  

    I have 4 lines on RS232 that should either be passed if those lines are being used, or be pulled down (per USB standard) if not in use.  I think I will just need 4 SPDT switches that all can support +-12V at up to 115200 baud rate.  Can you recommend a part that might work for this, preferable integrated into one package but I know that is hard.  Any sort of MUX or decoder would probably work if it supports the voltages

    Thanks so much,

    Jackson

  • 0 in reply to Jackson Thomas
    TI__Expert 3900 points
    Jackson,

    To support a ±12V input swing we have 3 families of devices. The first being the MUX36xxx family. This is our low leakage, low capacitance muxs that operate up to 36V signal swing. This family has an 8:1 configuration and a differential 4:1 (essentially 2 channels of 4:1).

    The next family is the MUX50x, which is similar in operation to the MUX36xxx family except it is not low leakage or as low capacitance. The configurations offered are the same though.

    Lastly we have the CD405xB family. This family comes with 3 configurations: an 8:1, differential 4:1, and SPDT 3channel device (CD4053B). THe CD4053B almost fits the bill but is one channel short if you use a single device.

    All of the above families of devices fit into the higher Ron category with around 125Ω on resistance. Depending on your application you may have to account for this.

    Looks like you are going to need either two devices of the 4:1 differential devices (MUX36D04, MUX509), or two of the CD4053B.


    Let me know if you need more clarity on the above options.