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DS1721 Schematic ( PDF Datasheet ) - Dallas

Teilenummer DS1721
Beschreibung 2-Wire Digital Thermometer and Thermostat
Hersteller Dallas
Logo Dallas Logo 




Gesamt 16 Seiten
DS1721 Datasheet, Funktion
www.dalsemi.com
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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DS1721 Datasheet, Funktion
DS1721
R0, R1 = Thermometer Resolution Bits. Table 3 below defines the resolution of the digital thermometer,
based on the settings of these two bits. There is a direct tradeoff between resolution and conversion time,
as depicted in the DC Electrical Characteristics: Digital Thermometer table. The designer has read/write
access to R0 and R1, and the default state is R0="1" and R1="1" (12-bit conversions).
THERMOMETER RESOLUTION CONFIGURATION Table 3
THERMOMETER
R1 R0 RESOLUTION
0 0 9-BIT
0 1 10-BIT
1 0 11-BIT
1 1 12-BIT
MAX
CONVERSION
TIME
0.15s
0.3s
0.6s
1.2s
X = Undefined. These bits are used internally by the DS1721.
DONE = Temperature Conversion Status Bit. "1" = conversion complete and "0" = conversion in
progress. The DONE bit is read-only, and the power-up state is "1". In the continuous conversion mode,
DONE = "0".
Thermostat Setpoints Programming
The thermostat registers (TH and TL) define the setpoints for operation of the TCOM output. The
respective register can be accessed over the 2-wire bus via the Access TH (A1h) or Access TL (A2h)
commands. Reading from or writing to the respective register is controlled by the state of the R/ W bit in
the 2-wire control byte (See “2-Wire Serial Data Bus” section).
The format of the TH and TL registers is a 12-bit 2’s complement representation of the temperature in °C.
The user can program the number of bits (9, 10, 11, or 12) for each TH and TL that correspond to the
thermometer resolution configuration chosen. If the 9-bit mode is chosen, for example, the 3 least
significant bits of TH and TL will be ignored by the thermostat comparator. The format for both TH and
TL is shown in Figure 4. The power-up default of TH is 80°C and that for TL is 75°C.
TEMPERATURE/DATA RELATIONSHIPS Figure 4
S 26 25 24 23 22
MSb
(UNIT = °C)
2-1 2-2 2-3 2-4
0
0
21 20 MSB
LSb
0 0 LSB
TEMP
+80°C
+75°C
+10.125°C
+0.5°C
+0°C
-0.5°C
-10.125°C
-25.0625°C
-55°C
DIGITAL OUTPUT
(Binary)
0101 0000 0000 0000
0100 1011 0000 0000
0000 1010 0010 0000
0000 0000 1000 0000
0000 0000 0000 0000
1111 1111 1000 0000
1111 0101 1110 0000
1110 0110 1111 0000
1100 1001 0000 0000
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DIGITAL OUTPUT
(Hex)
5000h
4B00h
0A20h
0080h
0000h
FF80h
F5E0h
E6F0h
C900h

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DS1721 pdf, datenblatt
DS1721
SAMPLE COMMAND SEQUENCE Table 5
Example: After power-up, initiates a temperature conversion, bus master reads temperature
BUS MASTER DS1721 DATA (MSB COMMENTS
MODE
MODE
FIRST)
TX RX START Bus Master initiates a START condition
TX RX <address, 0> Bus Master sends DS1721 address; R/ W = 0
RX
TX
ACK
DS1721 generates acknowledge bit
TX RX 51h Bus Master sends start convert T protocol
RX
TX
ACK
DS1721 generates acknowledge bit
TX RX START Bus Master initiates a repeated START condition
TX RX <address, 0> Bus Master sends DS1721 address; R/ W = 0
RX
TX
ACK
DS1721 generates acknowledge bit
TX
RX
AAh
Bus Master sends read temperature protocol
RX
TX
ACK
DS1721 generates acknowledge bit
TX RX START Bus Master initiates a repeated START condition
TX RX <address, 1> Bus Master sends DS1721 address; R/ W =1
RX
TX
ACK
DS1721 generates acknowledge bit
RX TX <1 data byte> DS1721 transmits MSB of temperature
TX
RX
ACK
Bus Master generates acknowledge bit
RX TX <1 data byte> DS1721 transmits LSB of temperature
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