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PDF DS1720 Data sheet ( Hoja de datos )
| Número de pieza | DS1720 | |
| Descripción | Digital Thermometer and Thermostat | |
| Fabricantes | Dallas | |
| Logotipo |  |
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DS1720
PRELIMINARY
DS1720
Econo – Digital Thermometer and
Thermostat
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)
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
TLOW
TCOM
VDD
– High Temperature Trigger
– Low Temperature Trigger
– 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. 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.
030598 1/12
1 page  
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 configura-
tion register is defined as follows:
CONFIGURATION/STATUS REGISTER
DONE THF TLF NVB 1
0 CPU 1SHOT
where
DONE =
THF =
TLF =
NVB =
CPU =
1SHOT =
Conversion Done bit. 1=conversion com-
plete, 0=conversion in progress.
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.
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.
Nonvolatile Memory Busy Flag. 1=write to
an E2 memory cell in progress. 0=nonvol-
atile memory is not busy. A copy to E2
may take up to 10 ms.
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.
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 E2 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 (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 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
030598 5/12
5 Page 
DS1720
AC ELECTRICAL CHARACTERISTICS
PARAMETER
SYMBOL
Temperature Conversion Time
Data to CLK Setup
CLK to Data Hold
CLK to Data Delay
CLK Low Time
CLK High Time
CLK Frequency
CLK Rise and Fall
RST to CLK Setup
CLK to RST Hold
RST Inactive Time
CLK High to I/O High–Z
RST Low to I/O High–Z
Convert Pulse Width
NV Write Cycle Time
TTC
tDC
tCDH
tCDD
tCL
tCH
fCLK
tR, tF
tCC
tCCH
tCWH
tCDZ
tRDZ
tCNV
tWR
MIN
35
40
285
285
DC
100
40
125
250 ns
(–55°C to +125°C; VDD=2.7V to 5.5V)
TYP
MAX
UNITS NOTES
400 1000 ms
ns 6
ns 6
100 ns 6, 7, 8
ns 6
ns 6
1.75 MHz
6
500 ns
ns 6
ns 6
ns 6, 9
50 ns 6
50 ns 6
500 ms
10 50 ms 12
AC ELECTRICAL CHARACTERISTICS
PARAMETER
SYMBOL
MIN
(–55°C to +125°C; VDD=2.7V to 5.5V)
TYP
MAX
UNITS NOTES
Input Capacitance
I/O Capacitance
CI
CI/O
5
10
pF
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. ICC 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. tCWH 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.
030598 11/12
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet DS1720.PDF ] | |
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