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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.

Summary of content (12 pages)

PAGE 1
DS1720 PRELIMINARY DS1720 Econo – Digital Thermometer and Thermostat FEATURES PIN ASSIGNMENT • Requires no external components • Supply voltage range covers from 2.7V to 5.5V DQ 1 8 VDD CLK/CONV 2 7 THIGH RST 3 6 TLOW GND 4 5 TCOM • Measures temperatures from –55°C to +125°C in 0.5°C increments. Fahrenheit equivalent is –67°F to +257°F in 0.
PAGE 2
DS1720 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 measurement circuitry is shown in Figure 2. At the same time, the counter is then preset with a value determined by the slope accumulator circuitry. This circuitry is needed to compensate for the parabolic behavior of the oscillators over temperature.
PAGE 3
DS1720 TEMPERATURE MEASURING CIRCUITRY Figure 2 SLOPE ACCUMULATOR PRESET COMPARE LOW TEMPERATURE COEFFICIENT OSCILLATOR INC =0 HIGH TEMPERATURE COEFFICIENT OSCILLATOR SET/CLEAR LSB PRESET COUNTER TEMPERATURE REGISTER COUNTER STOP =0 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 temperature.
PAGE 4
DS1720 DETAILED PIN DESCRIPTION Table 2 PIN SYMBOL DESCRIPTION 1 DQ 2 CLK/CONV 3 RST Reset input pin for 3–wire communication port. 4 GND Ground pin. 5 TCOM High/Low Combination Trigger. Goes high when temperature exceeds TH; will reset to low when temperature falls below TL. 6 TLOW Low Temperature Trigger. Goes high when temperature falls below TL. 7 THIGH High Temperature Trigger. Goes high when temperature exceeds TH. 8 VDD Data Input/Output pin for 3–wire communication port.
PAGE 5
DS1720 OPERATION AND CONTROL The DS1720 must have temperature settings resident in the TH and TL registers for thermostatic operation. A configuration/status register is also used to determine the method of operation that the DS1720 will use in a particular application, as well as indicating the status of the temperature conversion operation. The configuration register is defined as follows: CONFIGURATION/STATUS REGISTER DONE THF TLF NVB 1 0 CPU 1SHOT where DONE = Conversion Done bit.
PAGE 6
DS1720 falling edge of the clock, and remain valid through the rising edge. When reading data from the DS1720, the DQ pin goes to a high impedance state while the clock is high. Taking RST low will terminate any communication and cause the DQ pin to go to a high impedance state. Data over the 3–wire interface is communicated LSB first.
PAGE 7
DS1720 DS1720 COMMAND SET Table 3 INSTRUCTION DESCRIPTION PROTOCOL 3–WIRE BUS DATA AFTER ISSUING PROTOCOL NOTES TEMPERATURE CONVERSION COMMANDS Read Temperature Reads last converted temperature value from temperature register AAh Read Counter Reads value of count remaining from counter A0h Read Slope Reads value of the slope accumulator A9h Start Convert T Initiates temperature conversion EEh Idle 1 Stop Convert T Halts temperature conversion 22h
PAGE 8
DS1720 FUNCTION EXAMPLE Example: CPU sets up DS1720 for continuous conversion and thermostatic function.
PAGE 9
DS1720 READ DATA TRANSFER Figure 4 RST tCCH tCC CLK tCDH tCDD tDC tCDZ DQ 0 1 LSB DATA 7 tRDZ MSB DATA PROTOCOL WRITE DATA TRANSFER Figure 5 tCWH RST tCCH tCC tCL tR tF CLK tCDH DQ 0 tDC tCH tDC 1 tDCH 7 LSB DATA MSB DATA PROTOCOL NOTE: tCL, tCH, tR, and tF apply to both read and write data transfer. RELATED APPLICATION NOTES The following Application Notes can be applied to the DS1720.
PAGE 10
DS1720 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature –0.5V to +7.0V –55°C to +125°C –55°C to +125°C 260°C for 10 seconds * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
PAGE 11
DS1720 AC ELECTRICAL CHARACTERISTICS PARAMETER SYMBOL (–55°C to +125°C; VDD=2.7V to 5.5V) MIN TYP MAX UNITS 400 1000 ms NOTES Temperature Conversion Time TTC Data to CLK Setup tDC 35 ns 6 CLK to Data Hold tCDH 40 ns 6 CLK to Data Delay tCDD ns 6, 7, 8 100 CLK Low Time tCL 285 ns 6 CLK High Time tCH 285 ns 6 CLK Frequency fCLK DC 1.
PAGE 12
DS1720 DS1720 TYPICAL THERMOMETER ERROR DS1720 TYPICAL THERMOMETER ERROR 4 3 2 UPPER SPEC LIMIT TYPICAL ERROR THERMOMETER ERROR (C) 1 –55 –25 –10 5 20 45 60 –1 –2 –3 LOWER SPEC LIMIT –4 –5 –6 AMBIENT TEMPERATURE (C) 030598 12/12 75 90 100 125