Datasheet

Operation STLM75
12/40 Doc ID 13296 Rev 12
2.2 Thermal alarm function
The STLM75 thermal alarm function provides user-programmable thermostat capability and
allows the STLM75 to function as a standalone thermostat without using the serial interface.
The OS
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) 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 output will be asserted.
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 output. Once the OS
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
can be programmed to operate with
any amount of hysteresis. The OS
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
then becomes inactive 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
in comparator mode.