Computer Circuit Board Chips Programmed Integrated Digital DS1821S

Computer Circuit Board Chips Programmed Integrated Digital DS1821S

DS1821S Programmable Digital Thermostat and Thermometer

FEATURES

Requires no external components

Unique 1-Wire® interface requires only one port pin for communication

Operates over a -55°C to +125°C (-67°F to +257°F) temperature range

Functions as a standalone thermostat with user-definable trip-points Provides 8-bit (1°C resolution) centigrade temperature measurements

Accuracy is ±1°C over 0°C to +85°C range Converts temperature to a digital word in 1 second (max)

Available in 3-pin PR35 and 8-pin SO packages

Applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermally sensitive system

                                                                                                                                                                    PIN DEscriptION

                                                                                      GND - Ground

                                                                                       DQ - Data In/Out and Thermostat Output

                                                                                       VDD - Power Supply

                                                                                       Voltage NC - No Connect

TEMPERATURE SENSOR FUNCTIONALITY

The core functionality of the DS1821 is its proprietary direct-to-digital temperature sensor, which provides 8-bit (1°C increment) centigrade temperature readings over the range of -55°C to +125°C. A block diagram of the temperature measurement circuitry is shown in Figure 2. This circuit measures the temperature by counting the number of clock cycles generated by an oscillator with a low temperature coefficient (temp-co) during a gate period determined by a high temp-co oscillator. The low temp-co counter is preset with a base count that corresponds to –55°C. If the counter reaches 0 before the gate period is over, the temperature register, which is preset to –55°C, is incremented by one degree, and the counter is again preset with a starting value determined by the slope accumulator circuitry. The preset counter value is unique for every temperature increment and compensates for the parabolic behavior of the oscillators over temperature. At this time, the counter is clocked again until it reaches 0. If the gate period is not over when the counter reaches 0, the temperature register is incremented again. This process of presetting the counter, counting down to zero, and incrementing the temperature register is repeated until the counter takes less time to reach zero than the duration of the gate period of the high temp-co oscillator. When this iterative process is complete, the value in the temperature register will indicate the centigrade temperature of the device.

TEMPERATURE/DATA RELATIonSHIP Table 2

Temperature

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