The original single-chip USB-to-UART bridge from Silicon Labs, in QFN-28, and one of the most common ways to put a serial port on USB. Everything is on-chip: the USB 2.0 full-speed transceiver, a 3.3 V regulator, the oscillator, and a 1 KB EEPROM holding the USB descriptors, so the whole design is the chip plus a couple of capacitors. It presents a virtual COM port to the host and moves data at up to 1 Mbps, with the standard modem-control lines. It powers a huge share of the cheap USB-TTL adapters. The newer CP2102N adds higher rates and GPIO. Runs from USB 5 V or 3.3 V.

Pinout

Pin	Name	Type	Function
1	DCD	input	Data Carrier Detect control input (active low). RS-232 modem control input; can be left unconnected when not used.
2	RI	input	Ring Indicator control input (active low). RS-232 modem control input; can be left unconnected when not used.
3	GND	power_in	Ground reference. Also connect the exposed center pad of the QFN-28 to GND.
4	D+	bidirectional	USB D+ data line. Connects directly to the USB connector D+ pin; integrated 1.5 kΩ pull-up for full-speed enumeration.
5	D-	bidirectional	USB D- data line. Connects directly to the USB connector D- pin.
6	VDD	power_in	3.0-3.6 V power supply input and 3.3 V voltage regulator output. When the on-chip regulator is used (REGIN from VBUS), VDD is driven by the regulator and requires a 4.7 µF + 0.1 µF decoupling capacitor to GND.
7	REGIN	power_in	5 V input to the on-chip voltage regulator (typ. 4.0-5.25 V). Requires a 1.0 µF + 0.1 µF decoupling capacitor to GND.
8	VBUS	input	VBUS sense input. Connect to the VBUS signal of the USB network; a 5 V level indicates a USB connection. Detection threshold typ. 1.8 V.
9	RST	bidirectional	Device reset (active low). Open-drain output of the internal POR/VDD monitor; an external source can initiate a system reset by driving this pin low for at least 15 µs.
10	NC	unconnected	No connect. Leave unconnected or tie to VDD.
11	SUSPEND	output	Active-low suspend indicator. Driven low when the CP2102/9 enters the USB suspend state (inverse of SUSPEND). Floats high momentarily during reset; a 10 kΩ pulldown to GND is recommended to hold it low on power-up.
12	SUSPEND	output	Active-high suspend indicator. Driven high when the CP2102/9 enters the USB suspend state.
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	NC	unconnected	No connect. Leave unconnected or tie to VDD.
17	NC	unconnected	No connect. Leave unconnected or tie to VDD.
18	NC	unconnected	Unused on the CP2102 - leave unconnected or tie to VDD. (On the pin-compatible CP2109, this pin is VPP, the EPROM programming supply; a 4.7 µF cap to GND maintains board compatibility.)
19	NC	unconnected	No connect. Leave unconnected or tie to VDD.
20	NC	unconnected	No connect. Leave unconnected or tie to VDD.
21	NC	unconnected	No connect. Leave unconnected or tie to VDD.
22	NC	unconnected	No connect. Leave unconnected or tie to VDD.
23	CTS	input	Clear To Send control input (active low). RS-232 handshake input; can be left unconnected when not used.
24	RTS	output	Request To Send control output (active low). RS-232 handshake output; can be left unconnected when not used.
25	RXD	input	Asynchronous UART receive data input.
26	TXD	output	Asynchronous UART transmit data output. Baud rates from 300 bps up to 921600 bps (1 Mbps peak).
27	DSR	input	Data Set Ready control input (active low). RS-232 modem control input; can be left unconnected when not used.
28	DTR	output	Data Terminal Ready control output (active low). RS-232 modem control output; can be left unconnected when not used.

Key specifications

Parameter	Value
Type	USB 2.0-to-UART bridge
USB	full-speed (virtual COM port)
Max UART rate	1 Mbps
Integrated	USB PHY + regulator + clock + 1 KB EEPROM
Modem control	RTS/CTS/DSR/DTR/DCD/RI
External parts	2 capacitors
Supply voltage	USB 5 V or 3.3 V
Package	QFN-28 (5x5 mm)

Ordering variants

Same part, different packaging or reel option.

CP2102-GMR (QFN-28)
CP2102-GM (QFN-28)

CAD (KiCad official)

Symbol: CP2102 (generated from datasheet; KiCad has only CP2102N)
Footprint: Package_DFN_QFN:QFN-28-1EP_5x5mm_P0.5mm_EP3.35x3.35mm
3D model: QFN-28 (KiCad packages3D)

Provenance

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

Datasheet: Silicon Labs datasheet (26 pp, sha256 f025d9c738e49065, 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