Spark Logic

CH340G USB-to-UART bridge connection guide

CH340G USB-to-UART bridge SOP-16 wiring guide with power, signal assignments, and bench checks.

SOP-16

16 contacts Current package

WCH · 3.9 mm body width · 1.27 mm lead pitch

Wire USB power and the 12 MHz crystal

Required

This setup uses USB VBUS to supply VCC and a separate V3 bypass capacitor. Leave unused handshake pins open. Choose a 12 MHz crystal for the board and match its load capacitors to the crystal specification. WCH shows 33 pF per side in its example.

100 nF between USB supply and GroundUSB supply100 nFGround
100 nF between Internal regulator and GroundInternal regulator100 nFGround
12 MHz between Crystal input and Crystal outputCrystal input12 MHzCrystal output
33 pF in WCH example between Crystal input and GroundCrystal input33 pF in WCH exampleGround
33 pF in WCH example between Crystal output and GroundCrystal output33 pF in WCH exampleGround

Bench checks

  • With power disconnected, verify V3 is isolated from VCC in this mode.
  • Verify that the host enumerates a USB serial device. If it does not, check VCC, V3, USB data polarity and crystal layout.

WCH CH340DS1, version 3B, §§5.1 and 7.2.

Connection scenarios

Test the UART in loopback

Unplug USB and jumper the bridge transmit output to its own receive input. Plug USB back in, open the enumerated port and disable local echo and flow control.

Bench checks

  • Send a short string at 9,600 bit/s, 8 data bits, no parity and 1 stop bit. The received bytes should match the transmitted bytes.
  • Remove the jumper before connecting another UART. Cross the two data lines, share ground and check the logic levels first.

WCH CH340DS1, version 3B, UART signal descriptions. Loopback is a bench test.

SOP-16 wiring map

Highlighted contacts are used in the required step or selected circuit. Select a contact to inspect it.

Top view. Match pin 1 to the package mark. The numbers advance counterclockwise.
Selected pin details

12 · DCD#

Input · Inputs

Data Carrier Detect, active low.

WCH CH340DS1, version 3B, §§3–5

Electrical limits · Pin in the reference

Models and documents

The interactive map covers the CH340G SOP-16. See CH340DS1 §3 for CH340C, CH340B and the smaller CH340 packages. Some variants use an internal clock and assign pins 7 and 8 differently.

CH340G
3.9 mm body width · 1.27 mm lead pitch