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Schematic Review for isolated USB to UART bridge with ADUM3166 and FT232RN

Category: Hardware
Product Number: ADUM3166

Dear ADI Team,

I am currently in the process of designing an isolated USB to UART interface. For that I am utilizing the ADUM3166 for the isolation part and the FT232RN as the USB to UART bridge. Since there are not a lot of reference designs available for the digital isolator, I would kindly ask whether it would be possible for you to do a review of the attached schematic.

Additionally, I have two short questions regarding the design:

  1. I am planning on using the PGOOD pin as an indicator on whether a USB cable is plugged in or not. From my understanding once, VDD2 is powered, PGOOD is logic low (0V) when no power is present on the primary side and logic high (+3.3V) when power is applied to the primary side. Is that correct?
  2. Since I am applying power to the FT232RN not from the USB connector but rather from the downstream system, is my system considered a self powered device? In that regard, is then the resistor divider on the reset pin required as stated in the datasheet of the FT232RN on page 20? Would you then forward the PGOOD signal to the divider at the reset pin? Or can the RESET pin continuously be pulled high as shown in the schematic without any problems since the digital isolator asserts the USB communication?

Any help on that matter would be greatly appreciated. Thank you very much.

Best regards,


  • Hi,

    you are basically using the ADuM3166 in a peripheral application and therefore PGOOD can be used for your purpose.

    for reference, that's how PGOOD works:

    I don't see anything wrong in your schematic at a high level.

    Yes, I would consider this a self-powered device. For further confirmation I would reach out to the FTDI support team.

    I have two questions:

    - where is the 3.3V coming from in side 1 of the barrier?

    - why do you need isolation? any details on your end application?