DS1721
2-Wire Digital Thermometer
and Thermostat
www.maxim-ic.com
FEATURES
PIN ASSIGNMENT
CꢀTemperature measurements require no
external components with ±1°C accuracy
CꢀMeasures temperatures from -55°C to
+125°C; Fahrenheit equivalent is -67°F to
+257°F
SDA
VDD
1
2
4
7
*
VDD
A0
A1
SDA
SCL
TOUT
GND
SCL
TOUT
A0
A1
A2
CꢀTemperature resolution is configurable from 9
to 12 (default) bits (0.5°C to 0.0625°C
resolution)
GND
A2
DS1721U
DS1721S
8-Pin SOIC (150-mil)
8-Pin µ-SOP
CꢀMaximum conversion time (9-bit resolution)
of 93.75 ms
PIN DESCRIPTION
CꢀThermostatic settings are user-definable
CꢀData is read/written via a 2-wire serial
interface (open drain I/O lines); 3-bit
addressability
SDA
SCL
GND
TOUT
A0
- 2-Wire Serial Data Input/Output
- 2-Wire Serial Clock
- Ground
- Thermostat Output Signal
- Chip Address Input
CꢀWide power supply range (2.7V - 5.5V)
CꢀApplications include personal computers,
cellular telephones, office equipment, or any
thermally sensitive system
A1
- Chip Address Input
A2
- Chip Address Input
VDD
- Power Supply Voltage (+5V)
Cꢀ8-pin, 150-mil SOIC package and 8-pin µSOP
package
DESCRIPTION
The DS1721 2-Wire Digital Thermometer and Thermostat provides 12-bit temperature readings, which
indicate the temperature of the device. Thermostatic settings and temperature readings are all
communicated to/from the DS1721 over a simple 2-wire serial interface. No additional components are
required; the device is truly a “temperature-to-digital” converter.
The DS1721 has three address bits that allow a user to multidrop up to eight sensors along the 2-wire bus,
greatly simplifying the bussing of distributed temperature sensing networks.
The thermal alarm output, TOUT, is active when the temperature of the device exceeds a user-defined
temperature TH. The output remains active until the temperature is equal to or below the user-defined
temperature TL, allowing for any hysteresis necessary. The active state of TOUT is configurable by the
user.
For applications that require faster conversion times, the user can adjust the readout resolution from 12 to
9 bits, effectively reducing the conversion time from 750ms (MAX) to 93.75 ms (MAX). This is
particularly useful in applications where temperature changes large magnitudes very rapidly.
Applications for DS1721 include personal computers/services, cellular telephones, office equipment, or
any microprocessor-based, thermally sensitive system.
1 of 17
110405