USB-HUB

Design

Since various USB tools do not require high speed, the USB chip uses Tang Ming 's FE1.1S, and its speed is USB2.0. This is an older USB one-to-four expansion chip. One of the USB channels is directly transferred to the USB-to-serial port chip, and the remaining three channels are led out through the USB female socket.

The USB to serial port uses Qinheng's CH340C/CH340G. CH340C is not allowed to require an external crystal oscillator, while CH340G requires an external 12M clock. Their pins are fully compatible.

USB part

U1 in the picture is FE1.1S, and its package is SSOP28. The circuit is also very simple. Pin 21 is the LDO in the chip that outputs 3.3V voltage. Note that VD33 must be connected to a larger filter capacitor. Here C3 is connected to 10uF. When the computer can find the USB hub device and keeps reconnecting and disconnecting, it means that the C3 capacitor is small.

Convert to serial port part

U2 in the picture is a USB to serial port chip. The CH340C is used here, and its package is SOP16. I did not draw the crystal oscillator X2 on the PCB. If you use CH340G, you can short-circuit J1 or string a resistor to use the clock signal of U1.