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Original question:

TUSB2036 in self powered mode: What do I do with upstream Vbus signal?

TUSB2036: DP0PUR with external transistor

Ryan M
Prodigy 40 points
Part Number: TUSB2036

Hello,

I'm wondering the same thing as a previous post. In some TI examples, a 1.5k resistor is connected directly between DP0 and DP0PUR while others use an external NPN with the base connected the 5V from USB. When would you use on config over the other? 

In my case, I have an embedded solution that has three USB devices on a single board, so I am using the TUSB2036 to provide one up-stream facing connector for the three devices. The TUSB2036 and USB devices have a 3.3V supply on the board and do not rely on the input USB 5V. It is also likely that the board will not always have the USB connection present, but I want it to enumerate when the USB is connected. 

Can you please provide recommendations on the DP0PUR connections as well as RESETn? I'm planning on connecting the 15k + 1uF RC with the on-board 3.3V.

Thanks

  • 0
    TI__Guru 64326 points
    Ryan,

    The device between the two configurations is that one is meant for Self powered USB Hubs and the other is meant for Bus Powered USB Hubs.
    An external 1.5K + NPN is recommended for use when in a Self powered USB Hub application. A 1.5K tied directly to DP0PUR is used in Bus powered applications. Since you have a self powered application the first option is recommended for two reasons. First, DP pull up is presented when Vbus is present to upstream port (indicates powered host is connected), this is necessary for the USB Host to "see" TUSB2036. Second, when TUSB2036 is powered on, the DP0PUR terminal is at 3.3V and if a unpowered USB host is connected (No Vbus) the NPN is to avoid driving DP current from the hub back into an unpowered host.

    Your passive reset on RESETn is good.