CP2102N-A02-GQFN20R

The CP2102N-A02-GQFN20R from Silicon Labs is a highly integrated USB-to-UART bridge controller in a compact 3 x 3 mm QFN-20 package with tape-and-reel packaging (1500 units/reel). It is part of the USBXpress family, designed to quickly add USB connectivity to any UART-based design without firmware development.

The CP2102N integrates a USB 2.0 full-speed function controller, USB transceiver, oscillator, and UART in a single chip. No external USB components are required: no crystal (integrated 48 MHz oscillator), no pull-up resistors (integrated USB transceiver), and no EEPROM (960-byte internal configuration ROM). This minimizes BOM count and PCB area.

The A02 firmware revision supports USB battery charger detection (BCS 1.2), 4 GPIO pins, and I2C interface for advanced configurations. The QFN20 package variant provides 4 GPIO pins but does not have separate VIO and VDD pins (unlike the QFN24 variant). GPIO functions include LED indicators (TX/RX activity), clock output, and general-purpose I/O.

The UART supports all standard handshaking and modem interface signals (CTS, RTS, DSR, DTR, DCD, RI) for full RS-232 compatibility. Data formats include 5/6/7/8 data bits, 1/1.5/2 stop bits, and odd/even/mark/space/no parity. Baud rates range from 300 baud to 3 Mbaud with fractional baud rate generation for non-standard rates.

The 512-byte transmit buffer and 512-byte receive buffer prevent data loss during USB latency spikes. Hardware (RTS/CTS) or software (Xon/Xoff) flow control is supported.

The 960-byte internal configuration ROM stores vendor ID, product ID, serial number, power descriptor, release number, and product description strings. All customization is performed through the Silicon Labs Xpress Configurator GUI, requiring no firmware development.

Virtual COM port (VCP) drivers are royalty-free for Windows, Mac, and Linux. The drivers create a standard COM port that existing serial applications can use without modification. Custom USB device drivers are also supported through the Silicon Labs Direct Driver.

The device operates from a single 3.0-3.6V supply, with an internal voltage regulator that can also accept 3.0-5.25V supply for the USB transceiver. Typical operating current is 9.5 mA at 3.3V. The CP2102N is pin-compatible with the earlier CP2104 in the QFN24 package variant.

**USB-to-UART Bridge:** The CP2102N translates between USB protocol and UART serial protocol. When data arrives from the USB host, the USB function controller parses the USB packets, strips the USB protocol overhead, and places the data into the TX buffer. The UART transmitter then serializes the data according to the configured baud rate, data format, and flow control settings, sending it out on the TX pin.

Conversely, data received on the RX pin is captured by the UART receiver, deserialized, and placed into the RX buffer. When the USB host polls the device, the USB function controller packages the RX buffer data into USB packets and sends it to the host.

**Integrated Oscillator:** The internal 48 MHz oscillator eliminates the need for an external crystal, saving BOM cost and board space. The oscillator has sufficient accuracy for USB full-speed operation (fractional frequency tolerance within USB specification).

**Configuration ROM:** The 960-byte internal ROM stores device descriptors that identify the USB device to the host. These include Vendor ID (VID), Product ID (PID), serial number string, and power descriptors. Silicon Labs provides a default VID/PID, or customers can purchase a unique VID/PID for custom applications. The Xpress Configurator GUI writes these settings to the ROM via the USB interface.

**USB Battery Charger Detection:** The BCS 1.2 charger detection circuitry identifies the type of USB charger connected (standard downstream port, charging downstream port, or dedicated charging port) and signals the result to the system via GPIO or I2C. This allows portable devices to draw higher charging current when connected to a wall charger.