DS1775 Datasheet, PDF (2/13 Pages) Dallas Semiconductor – SOT23-5 Digital Thermometer and Thermostat

DS1775
As a digital thermometer, the DS1775 is software compatible with the DS75 2–Wire Thermal Watchdog.
The DS1775 is assembled in a compact SOT23–5 package allowing for low–cost thermal
monitoring/control in space–constrained applications. The low thermal mass allows for time constants
previously only possible with thermistors.
Applications for the DS1775 include personal computers/servers/workstations, cellular telephones, office
equipment, or any thermally–sensitive system.
DETAILED PIN DESCRIPTION Table 1
PIN SYMBOL DESCRIPTION
PIN 1
SCL Clock input/output pin for 2-wire serial communication port. This input
should be tied to GND for standalone thermostat operation.
PIN 2
GND Ground pin.
PIN 3
O.S. Thermostat output Open-drain output becomes active when temperature
exceeds T_OS. Device configuration defines means to clear over-temperature
state.
PIN 4
PIN 5
V_DD
SDA
Supply Voltage 2.7V – 5.5V input power pin.
Data input/output pin for 2-wire serial communication port. In the standalone
thermostat mode, this input selects hysteresis.
OVERVIEW
A block diagram of the DS1775 is shown in Figure 1. The DS1775 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 DS1775
begins temperature conversions with the default resolution of 9 bits (0.5°C resolution). 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 DS1775 into a shutdown mode, under which the
sensor will complete and store the conversion in progress and revert to a low–power standby state. In
applications where small incremental temperature changes are critical, the user can change the conversion
resolution from 9 bits to 10, 11, or 12. Each additional bit of resolution approximately doubles the
conversion time. This is accomplished by programming the configuration register. The configuration
register defines the conversion state, thermometer resolution/conversion time, active state of the
thermostat output, number of consecutive faults to trigger an alarm condition, and the method to
terminate an alarm condition.
The user can also program over–temperature (T_OS) and under–temperature (T_HYST) setpoints for
thermostatic operation. The power–up state of T_OS is 80°C and that for T_HYST is 75°C. The result of each
temperature conversion is compared with the T_OS and T_HYST setpoints. The DS1775 offers two modes for
temperature control, the comparator mode and the interrupt mode. This allows the user the flexibility to
customize the condition that would generate and clear a fault condition. Regardless of the mode chosen,
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