I'm using a USB-UART IC with an MCU, which is powered from a battery.
The USB-UART IC is powered from USB connector, not from the battery, so that I don't need to open up a console every time when the switch goes off and on.
edit: I didn't draw it on the figure but the IC has an internal 3.3V regulator and every VDD is on the 3.3V level when the switch is on.
Now I'm worried about when the USB is plugged and the switch is still off.
The MCU document says that every input pin's maximum rating is VDD + 0.3, which would be 0.3 V when the MCU is not powered.
If the TX/RX pair on the USB-UART side goes high, will it destroy the pins on the MCU side?
If so, What do I need between the TX/RX pairs?