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CC2540: D+ D- Supply Connections to Active Host

Chris Yorkey
Genius 15925 points
Part Number: CC2540

Team,

Question for you from our customer regarding the CC2540.  They're using its USB channel (product is a Device). A user condition may occur where the supply for the 2540 is off but D+ and D- are connected to an active Host. Intuitively this seems like it should be allowed and should not cause any damage to the 2540. But so far looking at the datasheet for the 2540 and browsing thru the USB 2.0 standard we’ve yet to find evidence supporting this. The ID pin is unconnected and there’s a 1.5K Ohm pullup  resistor on D+.

 Is the 2540 safe under this operating condition? Can you point me to the evidence?

Thanks so much,
Chris

  • 0
    TI__Mastermind 21280 points
    Hi Chris,
    R92 is DNM so I believe operating the device in your scenario should be ok.
  • 0 in reply to FI
    TI__Genius 15925 points
    R92 on EVM, Fl? I'm not sure of the resistor designator on which design you are referring to, but I understand where you are coming from. Feel free to clarify.

    Regards,
    Chris
  • 0 in reply to Chris Yorkey
    TI__Genius 15925 points

    Team + Fl,

    DVDD is the digital supply for the CC2540. So the condition in question: DVDD = 0V, CC2540 off, but the host is powered on, VBUS = 5V, etc.   Please comment?

    TY,

    Chris

  • 0 in reply to Chris Yorkey
    TI__Genius 15925 points

    TI Friends & Family,

    CONFIRMED. 

    When VDD = 0 the host will not be able to sense the presence of the USB device because D+ and D- will be pulled low by host’s internal resistors. So this will be ok to do.

    However, the condition where VDD = 3.3V and VBUS = 0 is not allowed.

    From USB spec:

    The voltage source on the pull-up resistor must be derived from or controlled by the power supplied on the USB cable such that when VBUS is removed, the pull-up resistor does not supply current on the data line to which it is attached.

     Regards,

    Chris