CP2103-GMR from SKYWORKS SILICON LABS, in a QFN-28-EP(5x5). Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	RI	input	Ring Indicator modem control input (active low). Marked as optional - may be left unconnected when not used.
2	GND	power_in	Ground. Must be tied to ground.
3	D+	bidirectional	USB D+ differential data line. Connect directly to USB connector D+ (no external series resistor required).
4	D-	bidirectional	USB D- differential data line. Connect directly to USB connector D- (no external series resistor required).
5	VIO	power_in	I/O supply voltage input, 1.8 V to VDD. Sets the logic level for UART, GPIO, and control I/O so the CP2103 can interface to sub-3.3 V hosts. Tie to VDD if a separate I/O rail is not required.
6	VDD	power_in	3.0-3.6 V core supply. Also serves as the output of the on-chip 3.3 V regulator when REGIN is driven from a 5 V source (see Section 9, Voltage Regulator).
7	REGIN	power_in	5 V input to the internal LDO. Tie to VBUS when running from USB bus power; leave unconnected (or tie to VDD) in self-powered operation.
8	VBUS	input	VBUS sense input. Connect to the USB VBUS rail; a 5 V level indicates the device is attached to a USB host.
9	RST	bidirectional	Active-low device reset. Open-drain output of the internal power-on-reset / VDD monitor; an external source may pull this pin low for at least 15 µs to initiate a system reset.
10	NC	unconnected	No connect. Leave unconnected or tie to VDD.
11	SUSPEND	output	Active-low suspend indicator. Driven low when the CP2103 enters the USB suspend state. Marked optional - may be left unconnected when not used.
12	SUSPEND	output	Active-high suspend indicator. Driven high when the CP2103 enters the USB suspend state. Marked optional - may be left unconnected when not used.
13	NC	unconnected	No connect. Leave unconnected or tie to VDD.
14	NC	unconnected	No connect. Leave unconnected or tie to VDD.
15	NC	unconnected	No connect. Leave unconnected or tie to VDD.
16	GPIO.3	bidirectional	User-configurable digital I/O. Alternate functions (e.g., RS-485 transceiver enable, status LEDs, hardware suspend flag) are assigned via the on-chip EEPROM.
17	GPIO.2	bidirectional	User-configurable digital I/O. Alternate functions (e.g., RS-485 transceiver enable, status LEDs) are assigned via the on-chip EEPROM.
18	GPIO.1	bidirectional	User-configurable digital I/O. Alternate functions (e.g., RS-485 transceiver enable, status LEDs) are assigned via the on-chip EEPROM.
19	GPIO.0	bidirectional	User-configurable digital I/O. Alternate functions (e.g., RS-485 transceiver enable, status LEDs) are assigned via the on-chip EEPROM.
20	NC	unconnected	No connect. Leave unconnected or tie to VDD.
21	NC	unconnected	No connect. Leave unconnected or tie to VDD.
22	CTS	input	Clear-To-Send modem control input (active low). Marked optional - may be left unconnected when hardware handshaking is not used.
23	RTS	output	Request-To-Send modem control output (active low). Marked optional - may be left unconnected when hardware handshaking is not used.
24	RXD	input	Asynchronous UART receive data input.
25	TXD	output	Asynchronous UART transmit data output.
26	DSR	input	Data-Set-Ready modem control input (active low). Marked optional - may be left unconnected when not used.
27	DTR	output	Data-Terminal-Ready modem control output (active low). Marked optional - may be left unconnected when not used.
28	DCD	input	Data-Carrier-Detect modem control input (active low). Marked optional - may be left unconnected when not used.
EP	SGND	power_in	Signal ground / exposed center pad of the QFN-28 package. Must be soldered to the PCB ground plane for both electrical ground return and thermal dissipation.

Key specifications

Parameter	Value
Manufacturer	SKYWORKS SILICON LABS
Package	QFN-28-EP(5x5)
Category	Interface
Pins	29

Ordering variants

Same part, different packaging or reel option.

CP2103-GMR

CAD (KiCad official)

Symbol: CP2103-GMR
Footprint: Package_DFN_QFN:QFN-28-1EP_5x5mm_P0.5mm_EP3.35x3.35mm
3D model: QFN-28-EP(5x5) (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`cp2103-gmr.step`	313 KB	You want the bare part, or you mark your own boards.
`cp2103-gmr-etched.step`	2.3 MB	You want the part with `CP2103-GMR` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 580 faces against 182 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

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

Datasheet: SKYWORKS SILICON LABS datasheet (20 pp, sha256 1b1ae8e977966c33, retrieved 2026-08-17, tier: lcsc)
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