DS75U Datasheet, PDF (8/14 Pages) Maxim Integrated Products – Digital Thermometer and Thermostat

DS75
compared to the values in the T_OS and T_HYST registers, and then O.S. is updated based on the result of the
comparison and the operating mode. The number of T_OS and T_HYST bits used during the thermostat
comparison is equal to the conversion resolution set by the R1 and R0 bits in the configuration register.
For example, it the resolution is 9 bits, only the 9 MSbs of T_OS and T_HYST will be used by the thermostat
comparator.
The active state of the O.S. output can be changed via the POL bit in the configuration register. The
power-up default is active low.
If the user does not wish to use the thermostat capabilities of the DS75, the O.S. output should be left
floating. Note that if the thermostat is not used, the T_OS and T_HYST registers can be used for general
storage of system data.
Comparator Mode — When the thermostat is in comparator mode, O.S. can be programmed to operate
with any amount of hysteresis. The O.S. output becomes active when the measured temperature exceeds
the T_OS value a consecutive number of times as defined by the F1 and F0 fault tolerance (FT) bits in the
configuration register. O.S. then stays active until the first time the temperature falls below the value
stored in T_HYST. Putting the device into shutdown mode does not clear O.S. in comparator mode.
Thermostat comparator mode operation with FT = 2 is illustrated in Figure 4.
Interrupt Mode — In interrupt mode, the O.S. output first becomes active when the measured
temperature exceeds the T_OS value a consecutive number of times equal to the FT value in the
configuration register. Once activated, O.S. can only be cleared by either putting the DS75 into shutdown
mode or by reading from any register (temperature, configuration, T_OS, or T_HYST ) on the device. Once
O.S. has been deactivated, it will only be reactivated when the measured temperature falls below the
T_HYST value a consecutive number of times equal to the FT value. Again, O.S can only be cleared by
putting the device into shutdown mode or reading any register. Thus, this interrupt/clear process is
cyclical between T_OS and T_HYST events (i.e, T_OS, clear, T_HYST, clear, T_OS, clear, T_HYST, clear, etc.).
Thermostat interrupt mode operation with FT = 2 is illustrated in Figure 4.
Figure 4. O.S. OUTPUT OPERATION EXAMPLE
In this example the DS75
is configured to have a
T_OS
fault tolerance of 2.
Temperature
T_HYST
Inactive
O.S. Output - Comparator Mode
Active
Inactive
O.S. Output - Interrupt Mode
Active
Assumes a read
has occurred
Conversions
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