DS1720

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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 VDD RST CLK/CONV DQ TLOW THIGH TCOM 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 THIGH – High Temperature Trigger TLOW – Low Temperature Trigger TCOM – High/Low Combination Trigger VDD – 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 is driven high if the DS1720’s temperature is greater than or equal to a user–defined temperature TH. TLOW is driven high if the DS1720’s temperature is less than or equal to a user–defined temperature TL. TCOM 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.

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 DQ STATUS REGISTER AND CONTROL LOGIC TEMPERATURE SENSOR HIGH TEMP TRIGGER, TH LOW TEMP TRIGGER, TL DIGITAL COMPARATOR/LOGIC THIGH TLOW TCOM

TEMPERATURE MEASURING CIRCUITRY Figure 2 SLOPE ACCUMULATOR PRESET PRESETCOUNTER COUNTER =0 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 +1/2°C 0 00000001 0001h +0°C 0 00000000 0000h –1/2°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 1/2°C LSB, yielding the following 9–bit format: XXXXX XX1 1 1 0 01 11 0 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

TL TH T (°C) DS1720 030598 4/12 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 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 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 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 THIGH output. When the DS1720’s measured temperature equals or falls below the value stored in the low temperature regis- ter, 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 T COM output goes high when the measured tem- perature 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. THERMOSTAT OUTPUT OPERATION Figure 3

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 configura- tion register is defined as follows: CONFIGURATION/STATUS REGISTER DONE THF TLF NVB 1 0 CPU 1SHOT where DONE = Conversion Done bit. 1=conversion com- plete, 0=conversion in progress. THF = Temperature High Flag. This bit will be set to 1 when the temperature is greater than or equal to the value of TH. It will remain 1 until reset by writing 0 into this location or by removing power from the device. This feature provides a method of determining if the DS1720 has ever been subjected to temperatures above TH while power has been applied. TLF = Temperature Low Flag. This bit will be set to 1 when the temperature is less than or equal to the value of TL. It will remain 1 until reset by writing 0 into this location or by removing power from the device. This feature provides a method of determining if the DS1720 has ever been subjected to temperatures below TL while power has been applied. NVB = Nonvolatile Memory Busy Flag. 1=write to an E 2 memory cell in progress. 0=nonvol- atile memory is not busy. A copy to E2 may take up to 10 ms. CPU = CPU use bit. If CPU=0, the CLK/CONV pin acts as a conversion start control, when RST is low. If CPU is 1, the DS1720 will be used with a CPU communicating to it over the 3–wire port, and the operation of the CLK/CONV pin is as a normal clock in concert with DQ and RST. This bit is stored in nonvolatile E2 memory, capable of at least 50,000 writes. The DS1720 is shipped with CPU=0. 1SHOT = One–Shot Mode. If 1SHOT is 1, the DS1720 will perform one temperature conversion upon reception of the Start Convert T protocol. If 1SHOT is 0, the DS1720 will continuously perform tem- perature conversion. This bit is stored in nonvolatile E 2 memory, capable of at least 50,000 writes. The DS1720 is shipped with 1SHOT=0. For typical thermostat operation, the DS1720 will oper- ate in continuous mode. However, for applications where only one reading is needed at certain times, and to conserve power, the one–shot mode may be used. Note that the thermostat outputs (T HIGH , TLOW , TCOM ) will remain in the state they were in after the last valid temperature conversion cycle when operating in one– shot mode. OPERATION IN STAND–ALONE MODE In applications where the DS1720 is used as a simple thermostat, no CPU is required. Since the temperature limits are nonvolatile, the DS1720 can be programmed prior to insertion in the system. In order to facilitate operation without a CPU, the CLK/CONV pin (pin 2) can be used to initiate conversions. Note that the CPU bit must be set to 0 in the configuration register to use this mode of operation. Whether CPU=0 or 1, the 3–wire port is active. Setting CPU=1 disables the stand–alone mode. To use the CLK/CONV pin to initiate conversions, RST must be low and CLK/CONV must be high. If CLK/ CONV is driven low and then brought high in less than 10 ms, one temperature conversion will be performed and then the DS1720 will return to an idle state. If CLK/ CONV is driven low and remains low, continuous con- versions will take place until CLK/CONV is brought high again. With the CPU bit set to 0, the CLK/CONV will override the 1–shot bit if it is equal to 1. This means that even if the part is set for one–shot mode, driving CLK/ CONV low will initiate conversions. 3–WIRE COMMUNICATIONS The 3–wire bus is comprised of three signals. These are the RST (reset) signal, the CLK (clock) signal, and the DQ (data) signal. All data transfers are initiated by driv- ing the RST input high. Driving the RST input low termi- nates communication. (See Figures 4 and 5). A clock cycle is a sequence of a falling edge followed by a rising edge. For data inputs, the data must be valid during the rising edge of a clock cycle. Data bits are output on the

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. The command set for the 3–wire interface as shown in Table 3 is as follows; only these protocols should be written to the DS1720, as writing other proto- cols to the device may result in permanent damage to the part. Read Temperature [AAh] This command reads the contents of the register which contains the last temperature conversion result. The next nine clock cycles will output the contents of this reg- ister. Write TH [01h] This command writes to the TH (HIGH TEMPERA- TURE) register. After issuing this command, the next nine clock cycles clock in the 9–bit temperature limit which will set the threshold for operation of the T HIGH output. Write TL [02h] This command writes to the TL (LOW TEMPERA- TURE) register. After issuing this command, the next nine clock cycles clock in the 9–bit temperature limit which will set the threshold for operation of the TLOW output. Read TH [A1h] This command reads the value of the TH (HIGH TEM- PERATURE) register. After issuing this command, the next nine clock cycles clock out the 9–bit temperature limit which sets the threshold for operation of the T HIGH output. Read TL [A2h] This command reads the value of the TL (LOW TEM- PERATURE) register. After issuing this command, the next nine clock cycles clock out the 9–bit temperature limit which sets the threshold for operation of the T LOW output. Read Counter [A0h] This command reads the value of the counter byte. The next nine clock cycles will output the contents of this register. Read Slope [A9h] This command reads the value of the slope counter byte from the DS1720. The next nine clock cycles will output the contents of this register. Start Convert T [EEh] This command begins a temperature conversion. No further data is required. In one–shot mode, the tempera- ture conversion will be performed and then the DS1720 will remain idle. In continuous mode, this command will initiate continuous conversions. Stop Convert T [22h] This command stops temperature conversion. No fur- ther data is required. This command may be used to halt a DS1720 in continuous conversion mode. After issuing this command, the current temperature measurement will be completed, and then the DS1720 will remain idle until a Start Convert T is issued to resume continuous operation. Write Config [0Ch] This command writes to the configuration register. After issuing this command, the next eight clock cycles clock in the value of the configuration register. Read Config [ACh] This command reads the value in the configuration reg- ister. After issuing this command, the next eight clock cycles output the value of the configuration register.

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 data> Read Counter Reads value of count remaining from counter A0h <read data> Read Slope Reads value of the slope accumulator A9h <read data> Start Convert T Initiates temperature conversion EEh Idle 1 Stop Convert T Halts temperature conversion 22h Idle 1 THERMOSTAT COMMANDS Write TH Writes high temperature limit value into TH register 01h <write data> 2 Write TL Writes low temperature limit value into TL register 02h <write data> 2 Read TH Reads stored value of high tempera- ture limit from TH register A1h <read data> 2 Read TL Reads stored value of low temperature limit from TL register A2h <read data> 2 Write Config Writes configuration data to configura- tion register 0Ch <write data> 2 Read Config Reads configuration data from configu- ration register ACh <read data> 2 NOTES: 1. In continuous conversion mode, a Stop Convert T command will halt continuous conversion. To restart, the Start Convert T command must be issued. In one–shot mode, a Start Convert T command must be issued for every temperature reading desired. 2. Writing to the E2 typically requires 10 ms at room temperature. After issuing a write command, no further writes should be requested for at least 10 ms.

Example: CPU sets up DS1720 for continuous conversion and thermostatic function. CPU MODE DS1720 MODE (3–WIRE) DATA (LSB FIRST) COMMENTS TX RX 0Ch CPU issues Write Config command TX RX 00h CPU sets DS1720 up for continuous conversion TX RX Toggle RST CPU issues Reset to DS1720 TX RX 01h CPU issues Write TH command TX RX 0050h CPU sends data for TH limit of +40°C TX RX Toggle RST CPU issues Reset to DS1720 TX RX 02h CPU issues Write TL command TX RX 0014h CPU sends data for TL limit of +10°C TX RX Toggle RST CPU issues Reset to DS1720 TX RX A1h CPU issues Read TH command RX TX 0050h DS1720 sends back stored value of TH for CPU to verify TX RX Toggle RST CPU issues Reset to DS1720 TX RX A2h CPU issues Read TL command RX TX 0014h DS1720 sends back stored value of TL for CPU to verify TX RX Toggle RST CPU issues Reset to DS1720 TX RX EEh CPU issues Start Convert T command TX RX Toggle RST CPU issues Reset to DS1720

READ DATA TRANSFER Figure 4 RST CLK DQ tCC tCDH tDC tCDD tCDZ tCCH LSB DATA MSB DATA01 7 PROTOCOL tRDZ WRITE DATA TRANSFER Figure 5 RST CLK DQ PROTOCOL LSB DATA MSB DATA01 7 tCC tDC tCDH tCH tCL tCWH tF tCCH tDC tDCH tR 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. These notes can be obtained from the Dallas Semiconductor “Application Note Book”, via our web- site at http:\\\\www.dalsemi.com/, or through our faxback service at (972) 371–4441. in Temperature Control Applications” torola SPI Bus” Application Note 105: “High Resolution Temperature Measurement with Dallas Direct–to–Digital Tempera- ture Sensors” Sample DS1720 subroutines that can be used in con- junction with AN105 can be downloaded from the web- site or our Anonymous FTP Site.

ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground –0.5V to +7.0V Operating Temperature –55 °C to +125°C Storage Temperature –55 °C to +125°C Soldering Temperature 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. The Dallas Semiconductor DS1720 is built to the highest quality standards and manufactured for long term reliability. All Dallas Semiconductor devices are made using the same quality materials and manufacturing methods. However, the DS1720 is not exposed to environmental stresses, such as burn–in, that some industrial applications require. For specific reliability information on this product, please contact the factory in Dallas at (972) 371–4448. RECOMMENDED DC OPERATING CONDITIONS PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Supply VDD 2.7 5.5 V 1 Logic 1 VIH 2.0 VCC +0.3 V 1 Logic 0 VIL –0.3 +0.6 V 1 DC ELECTRICAL CHARACTERISTICS (–55°C to +125°C; VDD =2.7V to 5.5V) PARAMETER SYMBOL CONDITION MIN MAX UNITS NOTES Thermometer Error TERR 0°C to 85°C ±2.5 °C 10, 11 –55°C to +125°C See Typical Curve Logic 0 Output VOL 0.4 V 3 Logic 1 Output VOH 2.4 V 2 Input Resistance R I RST to GND DQ,CLK to VDD M Ω M Ω Active Supply Current ICC 0°C to +70°C 1 mA 4, 5 Standby Supply Current ISTBY 0°C to +70°C 1 µA 4, 5 SINGLE CONVERT TIMING DIAGRAM (STAND–ALONE MODE) tCNV CONV

AC ELECTRICAL CHARACTERISTICS (–55°C to +125°C; VDD =2.7V to 5.5V) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Temperature Conversion Time TTC 400 1000 ms Data to CLK Setup tDC 35 ns 6 CLK to Data Hold tCDH 40 ns 6 CLK to Data Delay tCDD 100 ns 6, 7, 8 CLK Low Time tCL 285 ns 6 CLK High Time tCH 285 ns 6 CLK Frequency fCLK DC 1.75 MHz 6 CLK Rise and Fall tR , tF 500 ns RST to CLK Setup tCC 100 ns 6 CLK to RST Hold tCCH 40 ns 6 RST Inactive Time tCWH 125 ns 6, 9 CLK High to I/O High–Z tCDZ 50 ns 6 RST Low to I/O High–Z tRDZ 50 ns 6 Convert Pulse Width tCNV 250 ns 500 ms NV Write Cycle Time tWR 10 50 ms 12 AC ELECTRICAL CHARACTERISTICS (–55°C to +125°C; VDD =2.7V to 5.5V) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Input Capacitance C I 5 pF I/O Capacitance C I/O 10 pF NOTES: 1. All voltages are referenced to ground. 2. Logic one voltages are specified at a source current of 1 mA. 3. Logic zero voltages are specified at a sink current of 4 mA. 4. I CC specified with DQ pin open and CLK pin at VDD . 5. ICC specified with VCC at 3.3V and RST=GND. 6. Measured at VIH = 2.0V or VIL = 0.6V. 7. Measured at VOH = 2.4V or VOL = 0.4V. 8. Load capacitance = 50 pF. 9. t CWH must be 10 ms minimum following any write command that involves the E2 memory. 10. See typical curve for specification limits outside 0°C to 85°C range. 11. Thermometer error reflects temperature accuracy as tested during calibration. 12. Writing to the nonvolatile memory should only take place in the 0°C to 70°C temperature range.

DS1720 TYPICAL THERMOMETER ERROR –55 –25 –10 5 20 45 60 75 90 100 DS1720 TYPICAL THERMOMETER ERROR THERMOMETER ERROR (C) AMBIENT TEMPERATURE (C) 125 2UPPER SPEC LIMIT TYPICAL ERROR LOWER SPEC LIMIT