Shutdown Mode
For power-sensitive applications, the DS75LV offers
a low-power shutdown mode. The SD bit in the
configuration register controls shutdown mode. When SD
is changed to 1, the conversion in progress is completed
and the result stored in the temperature register after
which the DS75LV goes into a low-power standby state.
The OS output is cleared if the thermostat is operating in
interrupt mode and OS remains unchanged in comparator
mode. The 2-wire interface remains operational in shut-
down mode, and writing a 0 to the SD bit returns the
DS75LV to normal operation.
Thermostat
The DS75LV thermostat has two operating modes, com-
parator mode and interrupt mode, which activate and
deactivate the open-drain thermostat output (OS) based
on user-programmable trip-points (T
OS
and T
HYST
). The
DS75LV powers up with the thermostat in comparator
mode, active-low OS polarity, over-temperature trip-point
(T
OS
) register set to 80°C, and the hysteresis trip-point
(T
HYST
) register set to 75°C. If these power-up settings
are compatible with the application, the DS75LV can be
used as a standalone thermostat (i.e., no 2–wire com-
munication required). If interrupt mode operation, active-
high OS polarity or different T
OS
and T
HYST
values are
desired, they must be programmed after power-up, so
standalone operation is not possible.
In both operating modes, the user can program the ther-
mostat fault tolerance, which sets how many consecutive
temperature readings (1, 2, 4, or 6) must fall outside of
the thermostat limits before the thermostat output is trig-
gered. The fault tolerance is set by the F1 and F0 bits in
the configuration register. At power-up the fault tolerance
is set to 1.
The data format of the T
OS
and T
HYST
registers is identical
to that of the temperature register (see Figure 3), i.e., a
2-byte two’s complement representation of the trip-point
temperature in degrees centigrade with bits 3 through 0
hardwired to 0. After every temperature conversion, the
measurement is compared to the values stored in the T
OS
and T
HYST
registers. The OS output is updated based on
the result of the comparison and the operating mode of the
IC. 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, if the resolution is 9 bits, only the 9 MSbs of T
OS
and T
HYST
are used by the thermostat comparator.
The active state of the OS 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 DS75LV, the OS 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 compara-
tor mode, 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 F1 and
F0 fault tolerance (FT) bits in the configuration register. OS
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 OS in comparator mode.
Thermostat comparator mode operation with FT = 2 is
illustrated in Figure 4.
Interrupt Mode: In interrupt mode, the OS 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, OS
can only be cleared by either putting the DS75LV into
shutdown mode or by reading from any register (temperature,
configuration, T
OS
, or T
HYST
) on the device. Once OS
has been deactivated, it is only reactivated when the
measured temperature falls below the T
HYST
value a
consecutive number of times equal to the FT value. Again,
OS can only be cleared by putting the device into shut-
down 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
.
DS75LV Digital Thermometer and Thermostat
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