Datasheet

DS1720
5 of 14
Higher resolutions may be obtained by reading the temperature, and truncating the 0.5°C bit (the LSB)
from the read value. This value is TEMP_READ. The value left in the counter may then be read by
issuing a READ COUNTER command. This value is the count remaining (COUNT_REMAIN) after the
gate period has ceased. The value of the slope accumulator may be read (using the READ SLOPE
command), yielding the number of counts per degree C (COUNT_PER_C) at that temperature. The actual
temperature may be then be calculated by the user using the following:
TEMPERATURE = TEMP_READ – 0.25 +
DETAILED PIN DESCRIPTION Table 2
PIN SYMBOL DESCRIPTION
1 DQ Data Input/Output pin for 3–wire communication port.
2
CLK/CONV
Clock input pin for 3–wire communication port. When the DS1720 is used in
a stand–alone application with no 3–wire port, this pin can be used as a
convert pin. Temperature conversion will begin on the falling edge of CONV .
3
RST
Reset input pin for 3–wire communication port.
4 GND
Ground pin.
5 T
COM
High/Low Combination Trigger. Goes high when temperature exceeds T
H
;
will reset to low when temperature falls below T
L
.
6 T
LOW
Low Temperature Trigger. Goes high when temperature falls below T
L
.
7 T
HIGH
High Temperature Trigger. Goes high when temperature exceeds T
H
.
8 V
DD
Supply Voltage. 2.7V – 5.5V input power pin.
OPERATION–THERMOSTAT CONTROLS
Three thermally triggered outputs, T
HIGH
, T
LOW
, and T
COM
, are provided to allow the DS1720 to be used
as a thermostat, as shown in Figure 3. When the DS1720’s temperature meets or exceeds the value stored
in the high temperature trip register, the output T
HIGH
becomes active (high) and remains active until the
DS1720’s measured temperature becomes less than the stored value in the high temperature register, TH.
The T
HIGH
output can be used to indicate that a high temperature tolerance boundary has been met or
exceeded, or as part of a closed loop system can be used to activate a cooling system and to deactivate it
when the system temperature returns to tolerance.
The T
LOW
output functions similarly to the T
HIGH
output. When the DS1720’s measured temperature
equals or falls below the value stored in the low temperature register, the T
LOW
output becomes active.
T
LOW
remains active until the DS1720’s temperature becomes greater than the value stored in the low
temperature register, T
L
. The T
LOW
output can be used to indicate that a low temperature tolerance
boundary has been met or exceeded, or as part of a closed loop system, can be used to activate a heating
system and to deactivate it when the system temperature returns to tolerance.
The T
COM
output goes high when the measured temperature meets or exceeds T
H
, and will stay high until
the temperature equals or falls below T
L
. In this way, any amount of hysteresis can be obtained.
(COUNT_PER_C– COUNT_REMAIN)
COUNT_PER_C