I am working on a project that will consist of a USB-C host and device. The idea is that the host will use the alternate mode pins of a USB-C connector to drive analog signals to peripherals on the device. To ensure that the user accidentally plugging the device into a computer (or any other USB port) does not cause any problems, I am trying to make sure I use the proper enumeration and negotiation protocols.
During enumeration / negotiation, how can I ensure that there is no activity on the TX/RX pair pins of the USB-C connector?
Any signals on the TX/RX pins can damage the analog peripherals on the device side. When not being driven by the host device, the TX/RX pins must be kept at the same potential (no DC bias) to avoid damage.
My original idea was to use transistors or MOSFETs to pull the TX/RX pins to either V+ or GND until alternate mode negotiation is done. This would protect the analog peripherals, but I'm not sure if it would damage any standard USB-C port on a computer (or mess up the enumeration process). An ideal solution would be to use an analog switch IC to disconnect the pins from the analog peripherals, but space is very limited and a solution size involving minimal components is preferred.
