9 Replies Latest reply on Mar 19, 2020 8:04 PM by VasanthR_91

    question about VBUS on 4200L running at 3.3. volts (smoke involved!)

    mish_288636

      Hi, we're working on a design using the cy8c4248azi-L485, powered by a 3.3. volt LDO being powered by the USB connector, and the VBUS from it also goes directly to the PSoC.  On a few occasions now, the PSoC has released its magic smoke when plugging it in.  The datasheet doesn't mention much about power sequencing or whether it's safe to apply VBus if the VDD rail isn't powered. (the 3.3 volt regulator takes a few microseconds to come up after the USB cable is plugged in).  I looked at the reference designs, but they seem to all just power the chip with the USB voltage.

         After the chips fail, the VBUS pin typically measures 1-3 ohms to ground.

       

        Are there any additional documents or recommendations about how to do this or if it's possible or what.

       

       

      Thanks!