DS1720
ECON-Digital Thermometer and
Thermostat
www.maxim-ic.com
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
DQ
1
8
VDD
CLK/CONV
2
7
THIGH
RST
3
6
TLOW
GND
4
5
TCOM
DS1720S 8-Pin SOIC (208-mil)
PIN DESCRIPTION
DQ
CLK/ CONV
RST
GND
THIGH
TLOW
TCOM
VDD
– 3–Wire Input/Output
– 3–Wire Clock Input and
Stand–alone
Convert Input
– 3–Wire Reset Input
– Ground
– High Temperature Trigger
– Low Temperature Trigger
– High/Low Combination Trigger
– Power Supply Voltage (3V-5V)
DESCRIPTION
The DS1720 Digital Thermometer and Thermostat provides 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.
THIGH 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.
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020106
DS1720
ORDER INFORMATION
ORDERING
NUMBER
DS1720S+
DS1720S+T&R
PACKAGE
MARKING
DS1720 (see note)
DS1720 (see note)
DESCRIPTION
DS1720 in Lead-Free 208mil 8-pin SO
DS1720 in Lead-Free 208mil 8-pin SO, 2500 Piece
Tape-and-Reel
DS1720S
DS1720
DS1720 in 208mil 8-pin SO
DS1720S/T&R
DS1720
DS1720 in 208mil 8-pin SO, 2500 Piece Tape-and-Reel
Note: A “+” symbol will also be marked on the package near the Pin 1 indicator.
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.
The DS1720 measures temperature by counting the number of clock cycles that an oscillator with a low
temperature coefficient goes through during a gate period determined by a high temperature coefficient
oscillator. The counter is preset with a base count that corresponds 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, indicating 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 circuitry is needed to compensate
for the parabolic behavior 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 necessary 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 accumulator) at a given temperature must be known.
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DS1720
DS1720 FUNCTIONAL BLOCK DIAGRAM Figure 1
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DS1720
TEMPERATURE MEASURING CIRCUITRY Figure 2
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. 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 conversion factor must be
used.
TEMPERATURE/DATA RELATIONSHIPS Table 1
TEMP
+85°C
+25°C
+½°C
+0°C
-½°C
-25°C
DIGITAL OUTPUT
(Binary)
0 10101010
0 00110010
0 00000001
0 00000000
1 11111111
1 11001110
DIGITAL OUTPUT
(Hex)
00AA
0032h
0001h
0000h
01FFh
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 ½°C LSB, yielding the following 9–bit
format:
MSB
X
X
X
X
X
X
X
LSB
1
1
T = -25°C
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1
0
0
1
1
1
0
DS1720
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 +
(COUNT_PER_C– COUNT_REMAIN)
COUNT_PER_C
DETAILED PIN DESCRIPTION Table 2
PIN
1
2
SYMBOL
DQ
CLK/ CONV
3
4
5
GND
TCOM
6
7
8
TLOW
THIGH
VDD
RST
DESCRIPTION
Data Input/Output pin for 3–wire communication port.
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 .
Reset input pin for 3–wire communication port.
Ground pin.
High/Low Combination Trigger. Goes high when temperature exceeds TH;
will reset to low when temperature falls below TL.
Low Temperature Trigger. Goes high when temperature falls below TL.
High Temperature Trigger. Goes high when temperature exceeds TH.
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.
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DS1720
THERMOSTAT OUTPUT OPERATION Figure 3
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. 1=conversion complete, 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 E2 memory cell in progress. 0=nonvolatile
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
temperature conversion. This bit is stored in nonvolatile E 2 memory, capable of at least 50,000 writes.
The DS1720 is shipped with 1SHOT=0.
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DS1720
For typical thermostat operation, the DS1720 will operate 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 (THIGH, 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 driving the RST input high. Driving the RST
input low terminates 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
protocols 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 register.
Write TH [01h]
This command writes to the TH (HIGH TEMPERATURE) 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
THIGH output.
Write TL [02h]
This command writes to the TL (LOW TEMPERATURE) 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.
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DS1720
Read TH [A1h]
This command reads the value of the TH (HIGH TEMPERATURE) 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 THIGH output.
Read TL [A2h]
This command reads the value of the TL (LOW TEMPERATURE) 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 TLOW 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
temperature 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 further 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 register. After issuing this command, the next eight
clock cycles output the value of the configuration register.
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DS1720
DS1720 COMMAND SET Table 3
3-WIRE BUS
DATA AFTER
ISSUING
INSTRUCTION
DESCRIPTION
PROTOCOL
PROTOCOL
TEMPERATURE CONVERSION COMMANDS
Read Temperature Temperature Reads last converted
AAh
temperature value from
temperature register
Read Counter
Reads value of count remaining
A0h
from counter
Read Slope
Reads value of the slope
A9h
accumulator
Start Convert T
Initiates temperature conversion
EEh
Idle
Stop Convert T
Halts temperature conversion
22h
Idle
THERMOSTAT COMMANDS
01h
Write TH
Writes high temperature limit
value into TH register
Write TL
Writes low temperature limit value
02h
into TL register
Read TH
Reads stored value of high
A1h
temperature limit from TH register
Read TL
Reads stored value of low
A2h
temperature limit from TL register
Write Config
Writes configuration data to
0Ch
configuration register
Read Config
Reads configuration data from
ACh
configuration register
NOTES
1
1
2
2
2
2
2
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.
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DS1720
FUNCTION EXAMPLE
Example: CPU sets up DS1720 for continuous conversion and thermostatic function.
DS1720 MODE
CPU MODE
(3-WIRE)
DATA (LSB FIRST)
COMMENTS
TX
RX
0Ch
TCPU issues Write Config command
TX
RX
00h
CPU sets DS1720 up for continuous
conversion
TX
RX
CPU issues Reset to DS1720
Toggle RST
TX
RX
01h
CPU issues Write TH command
TX
RX
0050h
CPU sends data for TH limit of +40°C
TX
RX
CPU issues Reset to DS1720
Toggle RST
TX
RX
02h
CPU issues Write TL command
TX
RX
0014h
CPU sends data for TL limit of +10°C
CPU issues Reset to DS1720
TX
RX
Toggle RST
TX
RX
A1h
CPU issues Read TH command
RX
TX
0050h
DS1720 sends back stored value of TH
for CPU to verify
TX
RX
CPU issues Reset to DS1720
Toggle RST
TX
RX
A2h
CPU issues Read TL command
RX
TX
0014h
DS1720 sends back stored value of TL
for CPU to verify
TX
RX
RST CPU issues Reset to DS1720
Toggle RST
TX
RX
EEh
CPU issues Start Convert T command
TX
RX
CPU issues Reset to DS1720
Toggle RST
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DS1720
READ DATA TRANSFER Figure 4
WRITE DATA TRANSFER Figure 5
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DS1720
ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
–0.5V to +6.0V
–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.
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
Supply
Logic 1
Logic 0
SYMBOL
VDD
VIH
VIL
MIN
2.7
0.7 x VDD
-0.5
TYP
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Thermometer Error
Thermometer
Resolution
Logic 0 Output
Logic 1 Output
Input Current on Each
Pin
Input Resistance
SYMBOL
TERR
Active Supply Current
Standby Supply Current
Thermal Drift
ICC
CONDITION
-55°C to +125°C
VOL
VOH
RI
ISTBY
0.4 < VI/O < 0.9 x
VDD
RST to GND
DQ, CLK to VDD
0°C to +70°C
0°C to +70°C
MAX
5.5
VDD + 0.3
0.3 x VDD
UNITS
V
V
V
(-55°C to +125°C; VDD=2.7V to 5.5V)
MIN
2.4
-10
MAX
±2.5
12
UNITS
°C
Bits
NOTES
0.4
3
2
+10
V
V
μA
1
1.5
±0.2
MΩ
MΩ
mA
μA
°C
1
1
SINGLE CONVERT TIMING DIAGRAM (STAND-ALONE MODE)
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NOTES
1
1
1
4
4
10
DS1720
AC ELECTRICAL CHARACTERISTICS
(-55°C to +125°C; VDD=2.7V to 5.5V)
PARAMETER
SYMBOL
Temperature Conversion
TTC
Time
Data to CLK Setup
tDC
CLK to Data Hold
tCDH
CLK to Data Delay
tCDD
CLK Low Time
tCL
CLK High Time
tCH
CLK Frequency
tCLK
CLK Rise and Fall
tR, tF
tCC
RST to CLK Setup
t
CLK to RST Hold
CCH
t
RST Inactive Time
CWH
CLK High to I/O High-Z
tCDZ
tRDZ
RST Low to I/O High-Z
Convert Pulse Width
tCNV
Input Capacitance
CI
I/O Capacitance
CI/O
TYP
EEPROM
MIN
MAX
750
35
40
150
285
285
DC
1.75
500
100
40
125
50
50
500 ms
250 ns
5
10
UNITS
ms
NOTES
ns
ns
ns
ns
ns
MHz
ns
ns
ns
ns
ns
ns
5
5
5, 6, 7
5
5
5
5
5
5, 8
5
5
9
pF
pF
AC ELECTRICAL CHARACTERISTICS
(-55°C to +125°C; VDD=2.7V to 5.5V)
PARAMETER
EEPROM Write Cycle Time
EEPROM Writes
EEPROM Data Retention
CONDITIONS
MIN
-55°C to +55°C
-55°C to +55°C
50k
10
TYP
MAX
10
UNITS
ms
Writes
Years
NOTES:
1.
2.
3.
4.
5.
6.
7.
8.
9.
All voltages are referenced to ground.
Logic one voltages are specified at a source current of 1 mA.
Logic zero voltages are specified at a sink current of 4 mA.
ISTBY, ICC specified with DQ, CLK/ CONV = VDD, and RST = GND.
Measured at VIH = 2.0V or VIL = 0.6V.
Measured at VOH = 2.4V or VOL = 0.4V.
Load capacitance = 50 pF.
tCWH must be 10 ms minimum following any write command that involves the E2 memory.
250ns is the guaranteed minimum pulse width for a conversion to start; however, a smaller pulse
width may start a conversion.
10. Drift data is based on a 1000hr stress test at +125°C with VDD = 5.5V.
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DS1720
DS1720 TYPICAL THERMOMETER ERROR
DS1720
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