Datasheet

Operation STTS75
12/41 Doc ID 13298 Rev 11
2.2 Thermal alarm function
The STTS75 thermal alarm function provides user-programmable thermostat capability and
allows the STTS75 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
when the temperature falls below the value stored in T
HYS
register for a consecutive number
of times as defined by the fault tolerance bits (FT1 and FT0). Putting the device into
shutdown mode does not clear OS
/INT in comparator mode.