DS75 Datasheet, PDF (2/13 Pages) Dallas Semiconductor – 2.Wire Thermal Watchdog

DS75
Applications for the DS75 include personal computers/servers, cellular telephones, office equipment, or
any microprocessor–based thermally–sensitive system.
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
O.S.
Thermostat output Becomes active when temperature exceeds T_OS. Device
configuration defines means to clear over–temperature state.
4
GND Ground pin.
5
A₂
Address input pin.
6
A₁
Address input pin.
7
A₀
Address input pin.
8
V_DD
Supply Voltage 2.7V – 5.5V input power pin.
OVERVIEW
A block diagram of the DS75 is shown in Figure 1. The DS75 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 DS75
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 DS75 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 DS75 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,
the O.S. output will become active only after the measured temperature exceeds the respective trippoint a
consecutive number of times; the number of consecutive conversions beyond the limit to generate an O.S.
is programmable. The power–up state of the DS75 is in the comparator mode with a single fault
generating an active O.S. Digital data is written to/read from the DS75 via a 2–wire interface, and all
communication is MSb first. Multipoint sensing is possible with the DS75 by uniquely setting the 3–bit
address of up to 8 parts on the 2–wire bus.
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