A tiny USB-to-Serial baord in just ~10x18 mm^2, powered by CH340X with DTR# supported.
KiCad 6.0.6
This PCB can be used with both CH340E and CH340X. For CH340X, TNOW can be replaced by DTR#, which is useful for UART download purpose.
If 5V IO voltage level is desired, 5V to VCC shall be shorten by 0Ω resistor, and R3 shall NOT be connected. LDO is not required and can be left unconnected.
If 3.3V IO voltage level is desired, 3V3 to VCC shall be shorten by 0Ω resistor, and R3 shall be connected. LDO is required and two 1μF capacitors should be connected.
If DTR# is desired, DTR shall be connected to OS (Open-Source) or PP (Push-Pull) by 4.7kΩ resistor, otherwise left unconnected.
USB to Serial Port Chip CH340 - NanjingQinhengMicroelectronics