DS1775 Datasheet, PDF (2/14 Pages) Dallas Semiconductor – SOT23-5 Digital Thermometer and Thermostat

DS1775
Table 1. Detailed Pin Description
PIN NAME
FUNCTION
1
SCL
Clock Input/Output for 2-Wire Serial Communication Port. This input should
be tied to GND for stand-alone thermostat operation.
2
GND Ground
Thermostat Output. Open-drain output becomes active when temperature
3
O.S. exceeds T_OS. Device configuration defines means to clear overtemperature
state.
4
V_DD Supply Voltage 2.7V to 5.5V Input Power Pin
5
SDA
Data Input/Output for 2-Wire Serial Communication Port. In the stand-alone
thermostat mode, this input selects hysteresis.
DETAILED DESCRIPTION
Figure 1 shows a block diagram of the DS1775. 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 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 overtemperature (T_OS) and undertemperature (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,
the O.S. output becomes active only after the measured temperature exceeds the respective trip-point 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 DS1775 is in the comparator mode with a single fault
generating an active O.S.
Digital data is written to/read from the DS1775 via a 2-wire interface, and all communication is MSb
first.
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