8 Replies Latest reply on May 11, 2020 8:57 PM by YashwantK_46

    Is normal PC(host) <=> FX3 communication possible without a connection to 5V usb rail -> Vbus pin

    maVa_1182686

      I have a design that uses USB type C power delivery.

      5V rail USB is not 5V guaranteed, it can be as high as 20V(-Vdrop over cable) and as low as 5V(-Vdrop over cable)

       

      We can not connect straight to the FX3 for this reason, enabling PD would instantly destroy the FX3.

       

      I would like to power the USB PHY with 3.5V

      This is too low for the Vusb pin, but it's okay for the Vbatt pin.

      Firmware will start up normally from FLASH (this has been confirmed by cypress employees)

      BUT...

      I'm not sure if normal communication (for example, the bulk loop example) relies on ever seeing Vbus >= 4V.

       

      It could be that the powering via Vbatt only allows OTG functionality where the FX3 is host and that there is no way to have the FX3 function in the more general sense:

      = PC (host) <=> FX3

       

      I find the documentation very confusing and the newer DEVKIT does not allow you to test this use case!

       

       

      Thank You!