DS1720SSLASHT&R datasheet(5/14 Pages) MAXIM

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DS1720

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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

SYMBOL

DESCRIPTION

Data Input/Output pin for 3–wire communication port.

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 .

RST

Reset input pin for 3–wire communication port.

GND

Ground pin.

TCOM

High/Low Combination Trigger. Goes high when temperature exceeds TH;

will reset to low when temperature falls below TL.

TLOW

Low Temperature Trigger. Goes high when temperature falls below TL.

THIGH

High Temperature Trigger. Goes high when temperature exceeds TH.

VDD

Supply Voltage. 2.7V – 5.5V input power pin.

OPERATION–THERMOSTAT CONTROLS

Three thermally triggered outputs, THIGH, TLOW, and TCOM, 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 THIGH 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 THIGH 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 TLOW output functions similarly to the THIGH output. When the DS1720’s measured temperature

equals or falls below the value stored in the low temperature register, the TLOW output becomes active.

TLOW remains active until the DS1720’s temperature becomes greater than the value stored in the low

temperature register, TL. The TLOW 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 TCOM output goes high when the measured temperature meets or exceeds TH, and will stay high until

the temperature equals or falls below TL. In this way, any amount of hysteresis can be obtained.

(COUNT_PER_C– COUNT_REMAIN)

COUNT_PER_C

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