WCH CH340C PCB footprint, checks, and sourcing guide

The WCH CH340C is a USB-to-UART bridge with internal clock from Nanjing Qinheng Microelectronics. Its package or board interface is 16-pin SOP, and its relevant electrical envelope is 5 V operation with internal 3.3 V regulator/reference and configurable UART levels per reference design. It communicates or connects through USB 2.0 full-speed device to UART plus modem controls. Those fields belong together: substituting a familiar family name while changing package, voltage, sensing port, mount style, current class, or interface behavior can leave a PCB that passes ordinary net checks and still cannot be assembled or function safely.

CH340C adds an internal clock compared with crystal-requiring CH340G designs, reducing BOM but retaining WCH-specific supply and UART details.

Common uses include MCU programming ports and USB serial consoles. Start with the manufacturer drawing and recommended application, then record the exact ordering suffix alongside the KiCad symbol and footprint. This makes the library evidence reviewable when the part is re-sourced months later.

• Use the exact QFN/SSOP package and exposed-pad layout, with decoupling next to each supply pin. Keep the USB pair short and symmetric from receptacle protection to the bridge.
• Place crystal and load capacitors only if the selected bridge requires them. Keep UART handshakes and auto-reset transistors away from the USB differential pair.

Route USB directly with ESD and CC resistors, decouple VCC/V3 as specified, and use DTR/RTS transistors deliberately for target auto-reset/boot.

• Check whether the IC has an internal oscillator, USB pull-up, regulator, EEPROM, and factory-programmed identity. Set I/O voltage and UART levels to match the target MCU.
• Add USB-C CC resistors, ESD, and a deliberate VBUS/power path outside the bridge. Route D+ and D− over continuous ground and preserve test access to TX, RX, and handshake outputs.

Put the support components where their current, thermal, optical, RF, or measurement loops are actually short—not merely where ratsnest lines look tidy. Confirm pin one from the package view used in the datasheet, distinguish top view from mating face or bottom view, and check mask, paste, drill, courtyard, enclosure, and rework access independently. A correct copper pad pattern can still be a bad production footprint when the sensing opening, connector latch, exposed pad, thermal path, or cable volume is wrong.

MakeIRL’s release gate should not stop at “the symbol has the right number of pins.” For this part, a useful gate review combines ERC/DRC with the following package- and function-specific evidence:

1. Check USB polarity, pair routing, CC network, ESD, VBUS sensing/power, I/O rail, decoupling, oscillator requirements, reset, and exposed pad.
2. Check UART TX/RX crossover, voltage, auto-reset handshake polarity, bootloader timing, and any EEPROM/configuration needed for enumeration.
3. Check genuine MPN and driver support; counterfeit or re-marked USB bridges create field failures that schematic review cannot solve.
4. For WCH CH340C, check C suffix/internal-clock assumption, SOP pinout, VCC/V3 capacitor, USB pair, CC/ESD/VBUS, UART level, TX/RX, DTR/RTS polarity, and drivers.

Then run ERC and DRC, refill zones, and inspect the fabrication and assembly outputs. Cross-probe the exact pads named by any finding, compare the BOM MPN with the footprint and electrical limits above, and verify that a real cable, enclosure, antenna, sensor stimulus, load, or thermal path can be tested on the assembled unit. An exclusion is evidence that someone dismissed a marker; it is not evidence that the underlying condition was resolved.

The most expensive errors are usually plausible: a footprint from a sibling package, a breakout-board voltage copied to the bare IC, a headline current used without thermal analysis, or a connector family selected by pitch alone. For WCH CH340C, review these failure modes explicitly:

• Leaving CH340G crystal parts in the schematic or omitting CH340C's V3 capacitor by family-name substitution can prevent reliable enumeration.
• Crossing USB D+ and D− or UART TX/RX incorrectly because both interfaces use directional naming from different viewpoints.
• Assuming a 5 V USB supply means the bridge's UART outputs are safe for a 3.3 V-only MCU.

Sourcing note. Use genuine WCH CH340C and current signed drivers; control the exact suffix because CH340 family packages and clock needs vary. The approved vendor list should preserve manufacturer, full suffix, package, voltage/range/accuracy grade, lifecycle, and mating or external components. An alternate is real only after its datasheet, land pattern, electrical behavior, firmware assumptions, and assembly process have all been compared—not because a distributor search places it in the same parametric row.