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PDF DS1721 Data sheet ( Hoja de datos )
| Número de pieza | DS1721 | |
| Descripción | 2-Wire Digital Thermometer and Thermostat | |
| Fabricantes | Dallas | |
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DS1721
2-Wire Digital Thermometer
and Thermostat
FEATURES
Temperature measurements require no
external components with ±1°C accuracy
Measures temperatures from -55°C to
+125°C; Fahrenheit equivalent is -67°F to
+257°F
Temperature resolution is configurable from 9
to 12 (default) bits (0.5°C to 0.0625°C
resolution)
Maximum conversion time (9-bit resolution)
of 150 ms
Thermostatic settings are user-definable
Data is read/written via a 2-wire serial
interface (open drain I/O lines); 3-bit
addressability
Wide power supply range (2.7V - 5.5V)
Applications include personal computers,
cellular telephones, office equipment, or any
thermally sensitive system
8-pin, 150-mil SOIC package and 8-pin µSOP
package
PIN ASSIGNMENT
SDA
SCL
TOUT
GND
1
2
3
4
8 VDD
7
SDA
A0 SCL
1*
2
8 VDD
7 A0
6
A1 TOUT
3
6 A1
5 A2 GND 4
5 A2
DS1721S
8-Pin SOIC (150-mil)
DS1721U
8-PIN µ-SOP
PIN DESCRIPTION
SDA
- 2-Wire Serial Data Input/Output
SCL - 2-Wire Serial Clock
GND
- Ground
TOUT
A0
A1
A2
VDD
- Thermostat Output Signal
- Chip Address Input
- Chip Address Input
- Chip Address Input
- Power Supply Voltage (+5V)
DESCRIPTION
The DS1721 2-Wire Digital Thermometer and Thermostat provides 12-bit temperature readings which
indicate the temperature of the device. Thermostatic settings and temperature readings are all
communicated to/from the DS1721 over a simple 2-wire serial interface. No additional components are
required; the device is truly a “temperature-to-digital” converter.
The DS1721 has three address bits that allow a user to multidrop up to eight sensors along the 2-wire bus,
greatly simplifying the bussing of distributed temperature sensing networks.
The thermal alarm output, TOUT, is active when the temperature of the device exceeds a user-defined
temperature TH. The output remains active until the temperature is equal to or below the user-defined
temperature TL, allowing for any hysteresis necessary. The active state of TOUT is configurable by the
user.
For applications that require faster conversion times, the user can adjust the readout resolution from 12 to
9 bits, effectively reducing the conversion time from 1.2 s (MAX) to 150 ms (MAX). This is particularly
useful in applications where temperature changes large magnitudes very rapidly.
Applications for DS1721 include personal computers/services, cellular telephones, office equipment, or
any microprocessor-based, thermally sensitive system.
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111999
1 page  
DS1721
The active state for the totem-pole output is programmable by the user. The power-up default of the
DS1721 has TH=80°C, TL=75°C, and the output state active high. Refer to the “OPERATION-
Programming” section for instructions in adjusting the thermostat setpoints and TCOM active state.
THERMOSTAT OUTPUT OPERATION Figure 2
OPERATION-Programming
There are two areas of interest in programming the DS1721: the Configuration/Status register and the
thermostat setpoints. All programming is done via the 2-wire interface using the protocols discussed in
the “Command Set” section.
Configuration/Status Register Programming
The configuration/status register is accessed via the Access Config (ACh) function command. Writing to
or reading from the register is determined by the R/ W bit of the 2-wire control byte (See “2-wire Serial
Data Bus” section). Data is read from or written to the configuration register MSb first. The format of the
register is illustrated below in Figure 3. The effect each bit has on DS1721 functionality is described
below along with the power-up state of the bit and its ability to be read or written to. The entire register is
volatile and will always power-up in the default state. Therefore, it is recommended that the user issue
any configuration programming commands immediately after power is cycled, before any other
commands are issued.
CONFIGURATION/STATUS REGISTER Figure 3
DONE
X
X
U R1
MSb
R0
POL 1SHOT
LSb
1SHOT = Temperature Conversion Mode. If 1SHOT is "1", the DS1721 will perform and store one
temperature conversion upon reception of the Start Convert T (51h) command. If 1SHOT is "0", the
DS1721 will continuously perform temperature conversions and store the last completed result in the
Thermometer Register. The user has read/write access to the bit and the power-up default state is "0"
(continuous mode).
POL = TCOM Polarity Bit. If POL is "1", the active state of the TCOM output will be high. A "0" stored
in this location sets the thermostat output to an active low state. The user has read/write access to the
POL bit, and the power-up default state is "1" (active high).
U = Undefined. This bit is used internally by the DS1721. It will be a "0" at power-up and will change to
a "1" once the Start Convert T [51h] command is issued. This is a “Don’t Care” on a write; i.e. The
DS1721 will ignore writes to this location.
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DS1721
Stop Convert T [22h]
This command stops temperature conversion. No further data is required. This command may be used to
halt a DS1721 in continuous conversion mode. After issuing this command, the current temperature
measurement will be completed, stored and the DS1721 will remain idle until a Start Convert T is issued
to resume conversions.
DS1721 COMMAND SET Table 4
2-WIRE BUS DATA
INSTRUCTION
DESCRIPTION
PROTOCOL AFTER ISSUING
PROTOCOL
REGISTER COMMANDS
Access
Configuration
Writes to/Reads from 8-bit
configuration/status register
ACh
1 data byte
Access TH
Writes to/Reads from
12-bit TH register
A1h 1 or 2 data bytes
Access TL
Writes to/Reads from
12-bit TL register
A2h 1 or 2 data bytes
CONVERSION COMMANDS
Start Convert T
Initiates temperature
conversion
51h
idle
Stop Convert T
Terminates continuous
conversions
22h
idle
Read
Temperature
Reads 12-bit
Temperature register
AAh
Read 1 or 2 data bytes
NOTES
1
1, 3
1, 3
2
2
3
NOTES:
1. Data direction depends upon R/ W bit in the 2-wire control byte.
2. 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.
3. If the user only desires 8-bit thermometer readings, the master need only read 1 data byte and follow
with a NACK and STOP. If higher resolution is required, 2 bytes must be read.
11 of 16
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet DS1721.PDF ] | |
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