# CH341A

**WCH(Jiangsu Qin Heng)** · USB ICs · SOP-28-300mil

CH341A from WCH(Jiangsu Qin Heng), in a SOP-28-300mil. Pinout and pin descriptions extracted from the manufacturer datasheet (extract_pins, cross-checked by a second model); symbol, footprint, and 3D from KiCad-official CAD.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | ACT# | output | USB device configuration status output, active low: high while the USB device is unconfigured, low once configured; may drive an LED through a series current-limiting resistor. |
| 2 | RSTI | input | External reset input, active high with internal pull-down; the chip stays in reset while high and runs about 20 ms of delay after returning low. |
| 3 | IN7 | input | Custom general-purpose input in serial mode; datasheet recommends leaving it unconnected when unused (alternate function AS# in parallel mode). |
| 4 | ROV# | tri_state | Serial receive buffer overflow indicator, active low tri-state output; it should stay high in normal operation (alternate functions AFD# and DS# in printer and parallel modes). |
| 5 | TXD | output | Serial data output of the asynchronous UART; idles high (alternate functions ERR# in printer and parallel modes). |
| 6 | RXD | input | Serial data input of the asynchronous UART with internal pull-up; idles high (alternate function PEMP in printer and parallel modes). |
| 7 | INT# | input | Custom interrupt request input, rising-edge active, with internal pull-up. |
| 8 | IN3 | input | Custom general-purpose input in serial mode; datasheet recommends leaving it unconnected when unused (alternate function SLCT in printer and parallel modes). |
| 9 | V3 | power_in | At 3.3V supply it must be tied to VCC with a 3.0-3.6V input; at 5V supply it needs a 0.01uF to 0.1uF decoupling capacitor. |
| 10 | UD+ | bidirectional | USB D+ data line, connects directly to the USB bus; the chip has the USB pull-up built in. |
| 11 | UD- | bidirectional | USB D- data line, connects directly to the USB bus. |
| 12 | GND | power_in | Common ground, connected directly to the USB bus ground. |
| 13 | XI | input | Crystal oscillator input; CH341A requires an external 12 MHz crystal and load capacitor (or 12 MHz clock input at 11.98-12.02 MHz). |
| 14 | XO | output | Inverting crystal oscillator output; requires a 12 MHz crystal and load capacitor to XO and GND. |
| 15 | CTS# | input | Modem handshake input, clear to send, active low; controlled by the host application, not by the chip. |
| 16 | DSR# | input | Modem handshake input, data set ready, active low; controlled by the host application. |
| 17 | RI# | input | Modem handshake input, ring indicator, active low; controlled by the host application. |
| 18 | DCD# | input | Modem handshake input, carrier detect, active low; controlled by the host application. |
| 19 | OUT# | tri_state | Custom general-purpose output, active low tri-state; the host application sets its state. |
| 20 | DTR# | tri_state | Modem handshake output, data terminal ready, active low tri-state; set by the host application. |
| 21 | RTS# | tri_state | Modem handshake output, request to send, active low tri-state; set by the host application. |
| 22 | SLP# | tri_state | Sleep state output, active low tri-state (alternate function D7 in parallel and printer modes). |
| 23 | SDA | bidirectional | Open-drain configuration data line, with internal pull-up; configures chip function from an external 24Cxx EEPROM or via a direct SCL/SDA strap. |
| 24 | SCL | output | Open-drain configuration clock output with internal pull-up; connects to the SCL pin of an external serial EEPROM. |
| 25 | RDY# | output | Serial receive ready output, active low; high means the chip cannot yet receive data (reset, USB not configured, or receive buffer full). |
| 26 | TNOW | output | Serial transmit in progress indicator, active high; low again after transmission completes. |
| 27 | TEN# | input | Serial transmit enable input, active low, with internal pull-up; when high the chip pauses sending, so it must be low or grounded for the chip to transmit. |
| 28 | VCC | power_in | Positive supply input; 4.0-5.5V with V3 unconnected, or 3.0-3.6V with V3 tied to VCC; requires a 0.1uF decoupling capacitor. |

## Key specifications

| Parameter | Value |
|---|---|
| Manufacturer | WCH(Jiangsu Qin Heng) |
| Package | SOP-28-300mil |
| Category | Interface ICs |
| Pins | 28 |

## CAD (KiCad official)

- Symbol: `CH341A`
- Footprint: `Package_SO:SOP-28_8.4x18.16mm_P1.27mm`
- 3D model: SOP-28-300mil (KiCad packages3D, STEP)
- 3D model files: `ch341a-etched.step` / `ch341a-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `ch341a.step` / `ch341a.glb` are the bare package body.

## Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

- **Datasheet:** [WCH(Jiangsu Qin Heng) datasheet](docs/ch341a-datasheet.pdf) (12 pp, sha256 `8f76a55cf6fbe6fe`, retrieved 2026-10-27, tier: lcsc)
- **Datasheet language:** Chinese. Pin names, descriptions, and specs on this page were extracted and translated to English by ds2sf; the linked PDF is the manufacturer original.
- **Extractor:** parts-factory `2.0.0` / `extract_pins 0.3`, primary `claude-haiku-5-5` (text), consensus `claude-sonnet-5-5` (agreed), guards: pin_guards 0.1: passed. Pins are checked against the footprint pad set and their cited datasheet pages before publish.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/ch341a-datasheet.pdf)