Datasheet

DS75
7 of 14
Figure 3. TEMPERATURE, T
H
, and T
L
REGISTER FORMAT
bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8
MS Byte
S 2
6
2
5
2
4
2
3
2
2
2
1
2
0
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
LS Byte
2
-1
2
-2
2
-3
2
-4
0 0 0 0
Table 3. 12-BIT RESOLUTION TEMPERATURE/DATA RELATIONSHIP
TEMPERATURE
(°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
[phone] 0000 7D00h
+25.0625 0001 1001 0001 0000 1910h
+10.125 0000 1010 0010 0000 0A20h
+0.5 0000 0000 1000 0000 0080h
0 0000 0000 0000 0000 0000h
-0.5 1111 1111 1000 0000 FF80h
-10.125 1111 0101 1110 0000 F5E0h
-25.0625 1110 0110 1111 0000 E6F0h
-55 1100 1001 0000 0000 C900h
SHUTDOWN MODE
For power-sensitive applications, the DS75 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
will be completed and the result stored in the temperature register after which the DS75 will go into a
low-power standby state. The O.S. output will be cleared if the thermostat is operating in interrupt mode
and O.S will remain unchanged in comparator mode. The 2-wire interface remains operational in
shutdown mode, and writing a 0 to the SD bit returns the DS75 to normal operation.
OPERATION–THERMOSTAT
The DS75 thermostat has two operating modes, comparator mode and interrupt mode, which activate and
deactivate the open-drain thermostat output (O.S.) based on user-programmable trip-points (T
OS
and
T
HYST
). The DS75 powers up with the thermostat in comparator mode with active-low O.S. polarity and
with the 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 DS75 can be used
as a standalone thermostat (i.e., no 2–wire communication required). If interrupt mode operation, active-
high O.S. 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 thermostat 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 triggered. The fault tolerance is set by the F1 and F0 bits in the configuration and at
power-up the fault tolerance is 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 two-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 measured temperature is