Electronic – Powering USB to serial CH340 converter – does it need to be powered from USB port

raspberry piusb

I am creating simple expansion board for my Raspberry Pi with a few I2C components (EEPROM, RTC,…) and I would like to add a USB to serial converter to be able to connect to the RPi's serial port for debugging purposes (console access).

Until now I've been using a simple module with CH340 and I've decided to "just move" the chip onto my expansion board. Unfortunately the official CH340 datasheet is only in Chinese and the unofficial translation is not detailed enough.

I am not sure how to power the chip. In all examples it is powered from the USB port via voltage regulator (I need 3V3 logic for my RPi) however I have 3V3 available from RPi and I would like to power the CH340 chip from it to avoid using additional voltage regulator. Is this possible or does the CH340 need to be powered from the USB port?

Best Answer

It is not necessary to power the USB to serial converter device from the USB cable. There are plenty of "self powered" USB devices that are USB compliant.

I have made multiple products using a chip like the FTDI FT232RL and powered it from the local power rail of the MCU (in my case with that chip it was a local +5V).

You may still want to monitor the 5V coming from the USB connector so that you can tell if it is plugged into the upstream port. A simple connection of the USB 5V to a parallel pair of components (0.1uF capacitor to ground and a 10K resistor to ground) can then feed into the input of a 74LV14 to provide a USB VBUS detect.

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