78 Yuan Printer Flatbed Direct Supply Self-Starting Hub

The printer, purchased for 78 yuan from a seafood vendor (now unavailable), was too large to fit in a casing. This led to the idea of ​​making a hub. The universal SL2.1A chip has a drawback: after several firmware restarts following a direct connection to the STM32 motherboard, it loses its ID and becomes unconnectable, requiring a power disconnection. Thus, this self-starting hub based on the CH334R solution was born. The DC-DC converter is a TPS54302 with a 6~28V power input, which can be freely selected .
When soldering, ensure C1 and C2 have a withstand voltage of 35V or higher; other capacitors are normal. It is recommended to solder the DC-DC converter first, measure its voltage, and then solder the others .
A board thickness of 0.8mm is suggested. For automatic startup upon power-on, manual switching is not required; simply solder the two 3400 capacitors
 
. Regarding capacitors, some issues in the schematic diagram have not been resolved. Note that the 100NF and 10UF capacitors to the left of the 54202 need a withstand voltage of 35V or higher; other capacitors only need a withstand voltage higher than 5V. Electrolytic capacitors have been removed to save space. The peripheral circuitry for the 54202 follows the datasheet requirements; do not change the resistance or capacitance values.
PS: Remove the solder mask under the inductor before board fabrication.