Datasheet

DS75
8 of 14
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
fault tolerance of 2.
O.S. Output - Comparator Mode
Conversions
Inactive
Active
Temperature
T
OS
T
HYST
Inactive
Active
O.S. Output - Interrupt Mode
Assumes a read
has occurred