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TUSB321: VBUS_DET in DRP Mode

Part Number: TUSB321

Hi team,

If  the PORT pin is leaved to be floated to act as Dual Role Port(DRP), and a voltage above VBUS_DET threshold is applied to the pin VBUS_DET.  Would this make it to be a UFP(which means Rd to GND connected), despite the other device is  DFP or UFP ( which means if another device is UFP,  the attachment will not succeed )? Or TUSB321 will still toggle between DFP/UFP to attach the other device?

Thanks.

  • Since it's DRP, it will toggle Rp and Rd on CC pin. If the other side is Rd, then It will present Rp and configured as DFP.

    If the other side is Rp, then TUSB321 will present Rd and  configured as UFP and  debounces the CC pins and wait for VBUS detection before successfully attaching.

    regards,

    brian

  • Brian, thanks for your reply!

    In the USB Type-C R2.0 Spec 2.3.1,  "Power is not applied to the USB Type-C host or hub receptacle (VBUS or VCONN) until the
    Source detects the presence of an attached device (Sink) port. When a Source-to-Sink attach is detected, the Source is expected to enable power to the receptacle and proceed to normal USB operation with the attached device."

    What I want to know is what would happen if power is applied to VBUS before a sink device is attached (external power is firmed connected with VBUS)? It puzzles me a lot. 

  • Zach:

         In DFP  mode, Vbus must keep low until an UFP is attached successfully and ID goes low. That's why a vbus switch is needed in DFP mode to  controll the Vbus.

    Regarsd,

    brian' 

  • Very appreciated!

    Regards,

    zach