STDS75 Datasheet, PDF (12/37 Pages) STMicroelectronics – Digital temperature sensor and thermal watchdog

Operation
STDS75
2.2
Thermal alarm function
The STDS75 thermal alarm function provides user-programmable thermostat capability and
allows the STDS75 to function as a standalone thermostat without using the serial interface.
The OS/INT output is the alarm output. This signal is an open drain output, and at power-up,
this pin is configured with active-low polarity by default.
2.3
Comparator mode
In Comparator mode, each time a temperature-to-digital (T-to-D) temperature conversion
occurs, the new digital temperature is compared to the value stored in the T_OS and T_HYS
registers. If a fault tolerance number of consecutive temperature measurements are greater
than the value stored in the T_OS register, the OS/INT output will be activated.
For example, if the FT1 and FT0 Bits are equal to “10” (fault tolerance = 4), four consecutive
temperature measurements must exceed T_OS to activate the OS/INT output. Once the
OS/INT output is active, it will remain active until the first time the measured temperature
drops below the temperature stored in the T_HYS register.
When the thermostat is in comparator mode, the OS/INT can be programmed to operate
with any amount of hysteresis. The OS/INT output becomes active when the measured
temperature exceeds the T_OS value a consecutive number of times as defined by the FT1
and FT0 fault tolerance (FT) Bits in the configuration register. The OS/INT then stays active
until the first time the temperature falls below the value stored in T_HYS. Putting the device
into shutdown mode does not clear OS/INT in comparator mode.
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