Extremely accurate I2C real-time clock with an on-chip temperature-compensated crystal oscillator (TCXO) and crystal, in a SOIC-16W package. It tracks seconds through years with leap-year compensation to 2100, offers two time-of-day alarms, a programmable square-wave / interrupt output, a 32.768 kHz output, a battery-backup input, and a ±3 °C digital temperature sensor. The TCXO holds ±2 ppm, so it keeps time far better than a bare crystal RTC. Back it with a coin cell on VBAT to survive power loss.

Pinout

Pin	Name	Type	Function
1	32kHz	output	32.768kHz output. Open-drain; requires an external pullup resistor (to VCC or VBAT, up to 5.5V). May be left open if not used. Enabled via the EN32kHz bit in the status register.
2	VCC	power_in	DC power pin for primary supply (2.3V to 5.5V, typ 3.3V). Decouple with a 0.1µF to 1.0µF capacitor. If not used, connect to ground.
3	INT/SQW	output	Active-low interrupt or square-wave output. Open-drain; requires an external pullup resistor. Function is selected by the INTCN bit in the Control Register (0Eh): INTCN=0 outputs a square wave at frequency set by RS1/RS2, INTCN=1 asserts on an alarm match. May be left open if not used.
4	RST	bidirectional	Active-low reset input/output. Open-drain with internal ~50kΩ pullup to VCC. Driven low when VCC falls below VPF (power-fail); also accepts a debounced pushbutton input to ground for external reset request. Leave open or add a pushbutton switch to GND if not used.
5	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
6	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
7	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
8	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
9	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
10	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
11	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
12	N.C.	unconnected	No connection. Must be connected to ground per datasheet.
13	GND	power_in	Device ground reference. Substrate is connected to ground.
14	VBAT	power_in	Backup power-supply input (2.3V to 5.5V, typ 3.0V). Decouple with a 0.1µF to 1.0µF low-leakage capacitor. If not used, connect to ground. UL-recognized against reverse charging when used with a lithium battery.
15	SDA	bidirectional	I2C serial data input/output. Open-drain; requires an external pullup resistor. Supports Fast-mode (400kHz) I2C.
16	SCL	input	I2C serial clock input. Used to synchronize data on the serial interface. Supports Fast-mode (400kHz) I2C.

Key specifications

Parameter	Value
Type	I2C real-time clock (TCXO)
Accuracy	±2 ppm (0 to +40 °C)
Timekeeping	s/min/hr/day/date/month/year to 2100
Alarms	Two programmable time-of-day
Outputs	32.768 kHz + INT/SQW (open-drain)
Temperature sensor	±3 °C digital
Supply (VCC)	2.3-5.5 V (typ 3.3 V)
Backup (VBAT)	2.3-5.5 V (typ 3.0 V)
Package	SOIC-16W (300-mil)
Body (L×W×H)	10.3 × 7.5 × 2.67 mm

Ordering variants

Same part, different packaging or reel option.

DS3231SN# (SOIC-16W, industrial)
DS3231S# (SOIC-16W, commercial)

CAD (KiCad official)

Symbol: Timer_RTC:DS3231M (pins 5-12 relabeled N.C. for DS3231)
Footprint: Package_SO:SOIC-16W_7.5x10.3mm_P1.27mm
3D model: SOIC-16W (KiCad packages3D)

Provenance

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

Datasheet: Analog Devices datasheet (19 pp, sha256 dedc8cb80681a2eb, retrieved 2026-08-17, tier: cse)
Extractor: ds2sf (Claude) — every pin and dimension is cited to a datasheet page; refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF