MCP2221A USB Bridge

@@ -0,0 +1,59 @@+# MCP2221A++**Microchip** · USB Bridge · SOIC-14++The MCP2221A is a USB-2.0 to UART and I2C serial converter. It enumerates as a composite device (CDC for USB-to-UART, HID for I2C and configuration), and adds four GPIO pins with ADC and DAC functions. It is an easy way to bring USB connectivity, a serial port, and an I2C master into a design using standard OS drivers.++## Pinout++| Pin | Name | Type | Function |+|---|---|---|---|+| 1 | VDD | power_in | Positive supply input, 3.0V to 5.5V operating range. Decouple with a local ceramic capacitor. |+| 2 | GP0 | bidirectional | General purpose I/O. Alternate functions: SSPND (OUT) signals USB Suspend state; LED_URx (OUT, factory default) indicates UART Rx activity. |+| 3 | GP1 | bidirectional | General purpose I/O. Alternate functions: CLKR clock reference output (12 MHz or configurable divide), ADC1 input, LED_UTx (factory default) UART Tx activity indicator, and IOC external interrupt edge detector. |+| 4 | RST | input | Active-low reset input with internal pull-up. Drive low to reset the device. |+| 5 | URx | input | UART receive data input. Accepts data from the external UART peer to be forwarded to the USB CDC interface. |+| 6 | UTx | output | UART transmit data output. Drives data received over the USB CDC interface to the external UART peer. |+| 7 | GP2 | bidirectional | General purpose I/O. Alternate functions: USBCFG (OUT, factory default) indicates USB enumeration complete; ADC2 analog input; DAC1 analog output. |+| 8 | GP3 | bidirectional | General purpose I/O. Alternate functions: LED_I2C (OUT, factory default) USB/I2C traffic indicator; ADC3 analog input; DAC2 analog output. |+| 9 | SDA | bidirectional | I2C serial data line (open-drain). Requires external pull-up. MCP2221A operates as I2C host up to 400 kHz. |+| 10 | SCL | bidirectional | I2C serial clock line (open-drain). Requires external pull-up. Driven by the MCP2221A as I2C host, up to 400 kHz. |+| 11 | VUSB | power_out | USB internal 3.3V regulator output. Must be locally bypassed with a high-quality ceramic capacitor. Do not use to power external loads. |+| 12 | D- | bidirectional | USB differential data line, negative. Connect to the D- line of the USB connector. Termination is integrated. |+| 13 | D+ | bidirectional | USB differential data line, positive. Connect to the D+ line of the USB connector. Termination is integrated. |+| 14 | VSS | power_in | Device ground reference. |++## Key specifications++| Parameter | Value |+|---|---|+| Type | USB-to-UART + USB-to-I2C bridge |+| USB | Full-speed USB 2.0 (12 Mb/s), CDC + HID composite |+| UART | Up to 460.8 kbaud |+| I2C | Master, up to 400 kHz |+| GPIO | 4 pins with ADC (10-bit) and DAC (5-bit) functions |+| Supply voltage | 3.0 V to 5.5 V |+| Operating temperature | -40 C to 85 C |++## Ordering variants++- `MCP2221AI/P`+- `MCP2221AI/SL`+- `MCP2221AI/ST`+- `MCP2221AI/ML`++## CAD (KiCad official)++- Symbol: `mcp2221a.kicad_sym`+- Footprint: `mcp2221a.kicad_mod`+- 3D model: SOIC-14 body from KiCad `Package_SO/SOIC-14_3.9x8.7mm_P1.27mm`.++## Provenance++Data extracted from the manufacturer datasheet, not a distributor listing:++- **Datasheet:** [Microchip datasheet](https://ww1.microchip.com/downloads/en/DeviceDoc/MCP2221A-Data-Sheet-DS20005565D.pdf) (78 pp, sha256 `ade28a45a0314e2f`, retrieved 2026-08-17, tier: manufacturer)+- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.+- **CAD:** KiCad official libraries (CC-BY-SA 4.0).++[Datasheet PDF](docs/mcp2221a-datasheet.pdf)

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