I have this TTL-to-USB-serial device (supposedly from WINGONEER, who doesn't seem to have any documentation on how to use it):
I'm using it to hook up serial console on a system that has a 3.3V TTL serial debug connector with 4 pins: ground, tx rx, and a +3.3V supply. Since the USB adapter above produces 5V and 3.3V outputs on those pins, I left them unconnected. My expectation was that the adapter would only power up when the USB port is connected to a USB host, and that it would otherwise remain unpowered.
To my surprise, when I tried powering up the system it's connected to without the USB cable connected, the LEDs on the adapter lit and it seemed to be operational (power LED steady, activity LED flashing). Presumably it's drawing power over the RX line.
Is this potentially damaging?
I found the datasheet for the CP2102 chip and it indicates that the 3.3V can be configured as a supply or an output, but it seems to be configured as an output on this board. Would it be safe to hook it up?