Name: DS1720
SKU: DS1720
Price: 6.88805 USD
Availability: InStock

DS1720

Econo – Digital Thermometer and

Thermostat

DS1720

PRELIMINARY

030598 1/12

FEATURES

• Requires no external components

• Supply voltage range covers from 2.7V to 5.5V

• Measures temperatures from –55°C to +125°C in

0.5°C increments. Fahrenheit equivalent is –67°F to

+257°F in 0.9°F increments

• Temperature is read as a 9–bit value

• Converts temperature to digital word in 1 second

(max)

• Thermostatic settings are user–definable and non–

volatile

• Data is read from/written via a 3–wire serial interface

(CLK, DQ, RST

)

• Applications include thermostatic controls, industrial

systems, consumer products, thermometers, or any

thermally sensitive system

• 8–pin SOIC (208 mil) package

PIN ASSIGNMENT

GND

RST

CLK/CONV

LOW

HIGH

COM

DS1720S 8–PIN SOIC (208 MIL)

See Mech Drawings Section

PIN DESCRIPTION

DQ – 3–Wire Input/Output

CLK/CONV

– 3–Wire Clock Input and

Stand–alone

Convert Input

RST – 3–Wire Reset Input

GND – Ground

HIGH

– High Temperature Trigger

LOW

– Low Temperature Trigger

COM

– High/Low Combination Trigger

– Power Supply Voltage (3V – 5V)

DESCRIPTION

The DS1720 Digital Thermometer and Thermostat pro-

vides 9–bit temperature readings which indicate the

temperature of the device. With three thermal alarm out-

puts, the DS1720 can also act as a thermostat. T

HIGH

driven high if the DS1720’s temperature is greater than

or equal to a user–defined temperature TH. T

LOW

driven high if the DS1720’s temperature is less than or

equal to a user–defined temperature TL. T

COM

is driven

high when the temperature exceeds TH and stays high

until the temperature falls below that of TL.

User–defined temperature settings are stored in non–

volatile memory, so parts can be programmed prior to

insertion in a system, as well as used in stand–alone

applications without a CPU. Temperature settings and

temperature readings are all communicated to/from the

DS1720 over a simple 3–wire interface.

DS1720

030598 2/12

OPERATION–MEASURING TEMPERATURE

A block diagram of the DS1720 is shown in Figure 1.

The DS1720 measures temperatures through the use of

an on–board proprietary temperature measurement

technique. A block diagram of the temperature mea-

surement circuitry is shown in Figure 2.

The DS1720 measures temperature by counting the

number of clock cycles that an oscillator with a low tem-

perature coefficient goes through during a gate period

determined by a high temperature coefficient oscillator.

The counter is preset with a base count that corre-

sponds to –55°C. If the counter reaches zero before the

gate period is over, the temperature register, which is

also preset to the –55°C value, is incremented, indicat-

ing that the temperature is higher than –55°C.

At the same time, the counter is then preset with a value

determined by the slope accumulator circuitry. This cir-

cuitry is needed to compensate for the parabolic behav-

ior of the oscillators over temperature. The counter is

then clocked again until it reaches zero. If the gate

period is still not finished, then this process repeats.

The slope accumulator is used to compensate for the

nonlinear behavior of the oscillators over temperature,

yielding a high resolution temperature measurement.

This is done by changing the number of counts neces-

sary for the counter to go through for each incremental

degree in temperature. To obtain the desired resolution,

therefore, both the value of the counter and the number

of counts per degree C (the value of the slope accumu-

lator) at a given temperature must be known.

DS1720 FUNCTIONAL BLOCK DIAGRAM Figure 1

RST

ADDRESS

AND

RESET

CLK

STATUS REGISTER AND

CONTROL LOGIC

TEMPERATURE SENSOR

HIGH TEMP TRIGGER, TH

LOW TEMP TRIGGER, TL

DIGITAL COMPARATOR/LOGIC

HIGH

LOW

COM

DS1720

030598 3/12

TEMPERATURE MEASURING CIRCUITRY Figure 2

SLOPE ACCUMULATOR

PRESET

COUNTER

STOP

INC

COMPARE

TEMPERATURE REGISTER

LOW TEMPERATURE

COEFFICIENT OSCILLATOR

HIGH TEMPERATURE

COEFFICIENT OSCILLATOR

SET/CLEAR

LSB

This calculation is done inside the DS1720 to provide

0.5°C resolution. The temperature reading is provided

in a 9–bit, two’s complement reading by issuing a READ

TEMPERATURE command. Table 1 describes the

exact relationship of output data to measured tempera-

ture. The data is transmitted serially through the 3–wire

serial interface, LSB first. The DS1720 can measure

temperature over the range of –55°C to +125°C in 0.5°C

increments. For Fahrenheit usage, a lookup table or con-

version factor must be used.

TEMPERATURE/DATA RELATIONSHIPS

Table 1

TEMP

DIGITAL

OUTPUT

(Binary)

DIGITAL

OUTPUT

(Hex)

+85°C 0 10101010 00AA

+25°C 0 00110010 0032h

°C 0 00000001 0001h

+0°C 0 00000000 0000h

–

°C 1 11111111 01FFh

–25°C 1 11001110 01CEh

Since data is transmitted over the 3–wire bus LSB first,

temperature data can be written to/read from the

DS1720 as either a 9–bit word (taking RST low after the

9th (MSB) bit), or as two transfers of 8–bit words, with

the most significant 7 bits being ignored or set to zero,

as illustrated in Table 1. After the MSB, the DS1720 will

output 0s.

Note that temperature is represented in the DS1720 in

terms of a

°C LSB, yielding the following 9–bit format:

XXXXX XX1 11 001 110

MSB LSB

T = –25°C

Higher resolutions may be obtained by reading the tem-

perature, 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 remain-

ing (COUNT_REMAIN) after the gate period has

ceased. By loading the value of the slope accumulator

into the count register (using the READ SLOPE com-

mand), this value may then be read, yielding the number

of counts per degree C (COUNT_PER_C) at that tem-

perature. The actual temperature may be then be calcu-

lated by the user using the following:

TEMPERATURE = TEMP_READ – 0.25



(COUNT_PER_C – COUNT_REMAIN)

COUNT_PER_C

Part #	DS1720
Description	Temp Sensor Digital Serial8-Pin
Category	IC
Availability	In Stock
Qty	56

Qty	Price
1 - 11	$6.88805
12 - 23	$5.47913
24 - 35	$5.16604
36 - 47	$4.80076
48 +	$4.27894

DS1720

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