DS1721 2-Wire Digital Thermometer and Thermostat www.maxim-ic.com FEATURES PIN ASSIGNMENT Temperature measurements require no external components with 1C accuracy SDA V 1 8 DD * Measures temperatures from -55C to 18 SDA V DD 2 7 SCL A 0 +125C Fahrenheit equivalent is -67F to 27 A SCL 0 T 3 6 OUT A +257F 1 36 A T OUT 1 Temperature resolution is configurable from 9 4 5 45 GND A 2 A GND 2 to 12 (default) bits (0.5C to 0.0625C DS1721U DS1721S resolution) 8-Pin SOIC (150-mil) 8-Pin -SOP Maximum conversion time (9-bit resolution) of 93.75 ms PIN DESCRIPTION Thermostatic settings are user-definable SDA - 2-Wire Serial Data Input/Output Data is read/written via a 2-wire serial SCL - 2-Wire Serial Clock interface (open drain I/O lines) 3-bit GND - Ground addressability T - Thermostat Output Signal Wide power supply range (2.7V - 5.5V) OUT A - Chip Address Input Applications include personal computers, 0 A - Chip Address Input 1 cellular telephones, office equipment, or any A - Chip Address Input 2 thermally sensitive system V - Power Supply Voltage (+5V) DD 8-pin, 150-mil SOIC package and 8-pin SOP 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, T , is active when the temperature of the device exceeds a user-defined OUT 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 T is configurable by the OUT 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 DS1721 ORDERING INFORMATION ORDERING PACKAGE DESCRIPTION INFORMATION MARKING DS1721S DS1721 DS1721 in 150 mil 8-pin SO DS1721S+ DS1721 (See Note) DS1721 in Lead-Free 150 mil 8-pin SO DS1721S/T&R DS1721 DS1721 in 150 mil 8-pin SO, 2500 Piece Tape-and-Reel DS1721S+T&R DS1721 (See Note) DS1721 in Lead-Free 150 mil 8-pin SO, 2500 Piece Tape- and-Reel DS1721U 1721 DS1721 in 8-pin uSOP DS1721U+ 1721 (See Note) DS1721 in Lead-Free 8-pin uSOP DS1721U/T&R 1721 DS1721 in 8-pin uSOP, 3000 Piece Tape-and-Reel DS1721U+T&R 1721 (See Note) DS1721 in Lead-Free 8-pin uSOP, 3000 Piece Tape-and-Reel Note: A + symbol will also be marked on the package near the Pin 1 indicator. DETAILED PIN DESCRIPTION Table 1 PIN SYMBOL DESCRIPTION 1 SDA Data input/output pin. For 2-wire serial communication port. 2 SCL Clock input/output pin. For 2-wire serial communication port. 3 T Thermostat output. Active when temperature exceeds TH will reset when OUT temperature falls below TL. 4 GND Ground pin. 5 A2 Address input pin. 6 A1 Address input pin. 7 A0 Address input pin. 8 V Supply Voltage. 2.7V to 5.5V input power pin. DD OVERVIEW A block diagram of the DS1721 is shown in Figure 1. The DS1721 consists of five major components: 1. Precision temperature sensor 2. Analog-to-digital converter 3. 2-wire interface electronics 4. Data registers 5. Thermostat comparator The factory-calibrated temperature sensor requires no external components. Upon power-up, the DS1721 is in an idle mode. Upon issuance of a Start Convert T command 51h , the DS1721 begins temperature conversions with the default resolution of 12 bits (0.0625C resolution). Following an 8-bit command protocol, temperature data can be read over the 2-wire interface. The host can periodically read the value in the temperature register, which contains the last completed conversion. As conversions are performed in the background, reading the temperature register does not affect the conversion in progress. In power-sensitive applications, the user can put the DS1721 in a one-shot mode, under which the sensor will complete and store one temperature conversion and return to a low-power standby state. In time-sensitive applications, the user can change the conversion resolution from 12 bits to 9, 10, or 11. 2 of 17