Overview

The CH340G is a popular, low-cost USB-to-UART bridge IC produced by Nanjing Qinheng Microelectronics (WCH). It provides a full-duplex asynchronous serial UART interface with hardware modem control signals (RTS, CTS, DTR, DSR, DCD, RI) over a USB 2.0 Full-Speed (12 Mbps) physical layer.

Widely adopted across open-source hardware, budget microcontroller development boards (including Arduino Uno/Nano clones, ESP8266 NodeMCU, and ESP32 dev boards), and standalone USB-to-TTL serial adapters, the CH340G offers a direct replacement for FT232R and CP2102 ICs at a fraction of the cost. The CH340G variant operates with an external 12 MHz crystal resonator and features built-in 3.3V power regulator for internal transceiver logic.

Quick reference

FunctionUSB 2.0 to Full-Duplex UART Serial Bridge
Supply range3.3 V to 5.0 V DC
Baud rate50 bps to 2,000,000 bps (2 Mbps)
Required oscillator12.000 MHz Crystal / Ceramic Resonator
PackagesSOP-16 (150 mil width)
Logic level5 V TTL or 3.3 V CMOS

Pin configuration

PinNameTypeDescription
1GNDPowerGround connection (0 V)
2TXDOutputTransmit Data output (UART serial output to MCU RXD)
3RXDInputReceive Data input (UART serial input from MCU TXD, 5V tolerant)
4V3Power3.3V Internal Regulator Bypass. Connect to VCC for 3.3V mode; connect 100nF cap to GND in 5V mode
5UD+I/OUSB D+ Differential Signal Line
6UD-I/OUSB D- Differential Signal Line
7XIInput12 MHz Crystal Oscillator Input
8XOOutput12 MHz Crystal Oscillator Output
9CTS#InputClear To Send modem control input (active low)
10DSR#InputData Set Ready modem control input (active low)
11RI#InputRing Indicator modem control input (active low)
12DCD#InputData Carrier Detect modem control input (active low)
13DTR#OutputData Terminal Ready modem control output (active low, used for auto-reset)
14RTS#OutputRequest To Send modem control output (active low)
15RS232InputAuxiliary control pin (tie low for normal UART mode)
16VCCPowerPositive power supply input (3.3V or 5.0V)

Functional description

The CH340G contains a USB Function Controller, USB Transceiver, Serial Engine (SIE), FIFO Buffer, and Baud Rate Generator. On the USB side, it enumerates as a standard USB Communication Device Class (CDC) or proprietary WCH Serial COM Port.

On the UART side, the baud rate generator derives precision serial clocks from the external 12 MHz crystal input across standard baud rates (300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600, up to 2 Mbps). It supports 5, 6, 7, or 8 data bits, odd/even/mark/space/no parity, and 1 or 2 stop bits.

When VCC is supplied with 5.0V, an internal LDO generates a 3.3V reference on the V3 pin, which requires a 100 nF decoupling capacitor to ground. When operating natively on a 3.3V supply, V3 must be connected directly to VCC.

Absolute maximum ratings

Warning

Stresses beyond these values cause permanent damage. These are limits, not operating conditions.

ParameterRatingUnit
Supply Voltage (VCC)-0.5 to +6.0V
Input Voltage (RXD, CTS#, DSR#, RI#, DCD#)-0.5 to VCC + 0.5V
Operating Ambient Temperature-40 to +85°C
Storage Temperature-55 to +125°C

Electrical characteristics

ParameterSymbolMinTypMaxUnitConditions
Supply Voltage (5V Mode)VCC4.55.05.3VStandard 5V USB Bus
Supply Voltage (3.3V Mode)VCC3.03.33.6VDirect 3.3V VCC Mode
Operating CurrentICC41220mAActive UART transmission
Standby CurrentISB50150250µAUSB Suspend mode
High-Level Output VoltageVOHVCC - 0.5——VIOH = -4 mA (TXD, DTR#, RTS#)
Low-Level Output VoltageVOL——0.5VIOL = 4 mA
Input High VoltageVIH2.0—VCC + 0.5V5V TTL compatible
Input Low VoltageVIL-0.5—0.8V

Typical application

text
          +5V USB VBUS
               |
        +------+------+
        |             |
     100nF          10uF
        |             |
       GND           GND
        |             |
        +------+------+----------+
               |                 |
            +--+-----------------+--+
            | 16                4   |
            | VCC              V3   |
            |                       |
 USB D+ ----| 5 UD+                 |
 USB D- ----| 6 UD-        TXD  2 --+---> MCU RXD (5V or 3.3V)
            |                       |
  12MHz     | 7 XI         RXD  3 --+<--- MCU TXD
  +--[X1]---| 8 XO                  |
  |    |    |             DTR# 13 --+---> [100nF Cap] ---> MCU RESET
 22pF 22pF  |             GND   1   |
  |    |    +---------------+-------+
 GND  GND                   |
                           GND

Common mistakes

  • Missing 100 nF capacitor on V3 in 5V mode: If V3 is left floating without a decoupling capacitor when powered from 5V, internal logic becomes unstable causing random USB disconnects or dropped serial bytes.
  • Floating V3 when using 3.3V VCC: In 3.3V operation, V3 MUST be connected directly to VCC. Leaving it disconnected will cause the internal transceivers to fail to operate.
  • Incorrect Crystal Load Capacitors: The CH340G requires a 12.000 MHz crystal with two 22 pF load capacitors to ground. Omitting these caps or using a different crystal frequency (e.g. 16 MHz) will cause incorrect baud rates or USB enumeration failure.
  • TXD/RXD Line Swap: Remember that CH340G TXD connects to the target MCU's RXD, and CH340G RXD connects to the MCU's TXD.

Notes & further reading

  • Driver support: WCH provides official signed drivers for Windows (CH341SER.EXE), macOS, Linux (included in kernel 2.6.24+ as ch341), and Android.
  • DTR# Auto-Reset Circuit: Arduino boards place a 100 nF series capacitor between CH340G DTR# pin and the ATmega328P RESET# pin with a 10 kΩ pull-up to generate a low pulse when the IDE opens the serial port.

Assets & downloads