USB to Dual Serial Ports Chip CH9103


CH9103 is a USB bus converter chip, which converts USB to dual serial ports.

Each UART supports high-speed full-duplex and odd/even parity, provides standard MODEM signals, used to expand serial ports for computer or upgrade directly from normal serial device or MCU to USB bus.


  • Full-speed USB device interface, USB 2.0 compatible.
  • Built-in firmware, emulate standard UART interface, used to upgrade the original serial peripheral or expand additional UART via USB.
  • Original serial applications are totally compatible without any modification in Windows operating systems.
  • Supports free installation OS which built-in CDC driver or multi-functional high-speed VCP vendor driver.
  • Hardware full duplex UART interface, integrated independent transmit-receive buffer, supports communication baud rate varies from 50bps to 3Mbps.
  • UART supports 5, 6, 7 or 8 data bits, supports odd, even, space, mark and none parity.
  • Supports common MODEM interface signals RTS, DTR, DCD, DSR and CTS.
  • Supports CTS and RTS hardware automatic flow control.
  • Supports half-duplex, provides sending status TNOW, used for controlling RS485 to transmit-receive switch.
  • Supports RS232 interface, through external voltage conversion chip.
  • Supports 5V and 3.3V power supply voltages.
  • UART interface I/O powered independently, supports 5V, 3.3V, 2.5V, 1.8V power supply voltages.
  • Integrated power-on reset, integrated clock, no external crystal required.
  • Built-in EEPROM used to configure the chip of VID, PID, maximum current value, vendor and product information string, etc.
  • Integrated Unique ID (USB Serial Number).
  • RoHS compliant QFN40 lead-free package.


Note: The backplane is 0# pin GND, which is an optional but recommended connection; other GND are necessary connections.

The USB transceiver of CH9103 is designed according to the built-in design of USB2.0, and it is recommended that no external resistor is in series with UD+ and UD- pins.