Measures temperature over I2C and also acts as a standalone thermostat. It reports 9-bit readings (0.5 C steps) from -55 to 125 C, and a TOUT pin switches high or low when the temperature crosses user-set high and low registers, with programmable hysteresis, so it can drive a fan or heater without a host in the loop. Three address pins put up to eight on one bus. The settings are stored in nonvolatile memory. A self-contained temperature switch plus digital readout.

Pinout

Pin	Name	Type	Function
1	SDA	bidirectional	2-wire serial data input/output (open-drain). Requires external pull-up to VDD.
2	SCL	input	2-wire serial clock input/output (open-drain). Clock line for I²C-compatible communication.
3	TOUT	output	Thermostat output. Active when measured temperature exceeds TH; deasserts when temperature falls below TL, providing programmable hysteresis.
4	GND	power_in	Ground reference pin (0 V).
5	A2	input	Chip address input pin (MSB of 3-bit slave-address selector). Tie to VDD or GND to set device address on shared 2-wire bus.
6	A1	input	Chip address input pin. Tie to VDD or GND to set device address on shared 2-wire bus.
7	A0	input	Chip address input pin (LSB of 3-bit slave-address selector). Tie to VDD or GND to set device address on shared 2-wire bus.
8	VDD	power_in	Supply voltage input pin. Operating range 2.7 V to 5.5 V. Bypass to GND with a 0.1 µF capacitor close to the pin.

Key specifications

Parameter	Value
Type	Digital thermometer + thermostat
Interface	I2C (8 addresses)
Resolution	9-bit (0.5 C)
Range	-55 to 125 C
Thermostat output	TOUT with programmable trip + hysteresis
Nonvolatile	Trip points stored in EEPROM
Supply	2.7-5.5 V
Package	SOIC-8

Ordering variants

Same part, different packaging or reel option.

DS1621S+ (SOIC-8)
DS1621+ (PDIP-8)

CAD (KiCad official)

Symbol: Sensor_Temperature:DS1621 (KiCad official)
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOIC-8 (KiCad packages3D, STEP)

Provenance

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

Datasheet: Analog Devices datasheet (16 pp, sha256 faa68e65a7b2f8f0, 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