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DS18B20 の電気的特性と機能

DS18B20のメーカーはDallas Semiconductorです、この部品の機能は「Programmable Resolution 1-Wire Digital Thermometer」です。


製品の詳細 ( Datasheet PDF )

部品番号 DS18B20
部品説明 Programmable Resolution 1-Wire Digital Thermometer
メーカ Dallas Semiconductor
ロゴ Dallas Semiconductor ロゴ 




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DS18B20 Datasheet, DS18B20 PDF,ピン配置, 機能
www.dalsemi.com
FEATURES
Unique 1-Wire interface requires only one
port pin for communication
Multidrop capability simplifies distributed
temperature sensing applications
Requires no external components
Can be powered from data line. Power supply
range is 3.0V to 5.5V
Zero standby power required
Measures temperatures from -55°C to
+125°C. Fahrenheit equivalent is -67°F to
+257°F
±0.5°C accuracy from -10°C to +85°C
Thermometer resolution is programmable
from 9 to 12 bits
Converts 12-bit temperature to digital word in
750 ms (max.)
User-definable, nonvolatile temperature alarm
settings
Alarm search command identifies and
addresses devices whose temperature is
outside of programmed limits (temperature
alarm condition)
Applications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitive
system
PRELIMINARY
DS18B20
Programmable Resolution
1-Wire® Digital Thermometer
PIN ASSIGNMENT
DALLAS
DS1820
BOTTOM VIEW
123
123
DS18B20 To-92
Package
NC 1 8 NC
NC 2 7 NC
VDD 3 6 NC
DQ 4 5 GND
DS18B20Z
8-Pin SOIC (150 mil)
PIN DESCRIPTION
GND - Ground
DQ - Data In/Out
VDD - Power Supply Voltage
NC - No Connect
DESCRIPTION
The DS18B20 Digital Thermometer provides 9 to 12-bit (configurable) temperature readings which
indicate the temperature of the device.
Information is sent to/from the DS18B20 over a 1-Wire interface, so that only one wire (and ground)
needs to be connected from a central microprocessor to a DS18B20. Power for reading, writing, and
performing temperature conversions can be derived from the data line itself with no need for an external
power source.
Because each DS18B20 contains a unique silicon serial number, multiple DS18B20s can exist on the
same 1-Wire bus. This allows for placing temperature sensors in many different places. Applications
where this feature is useful include HVAC environmental controls, sensing temperatures inside buildings,
equipment or machinery, and process monitoring and control.
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DS18B20 pdf, ピン配列
DS18B20 BLOCK DIAGRAM Figure 1
DS18B20
64-BIT ROM
DQ AND
1-WIRE PORT
INTERNAL VDD
MEMORY AND
CONTROL LOGIC
SCRATCHPAD
TEMPERATURE SENSOR
HIGH TEMPERATURE
TRIGGER, TH
POWER
VDD SUPPLY
SENSE
8-BIT CRC
GENERATOR
LOW TEMPERATURE
TRIGGER, TL
CONFIGURATION
REGISTER
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power
whenever the DQ or VDD pins are high. DQ will provide sufficient power as long as the specified timing
and voltage requirements are met (see the section titled “1-Wire Bus System”). The advantages of
parasite power are twofold: 1) by parasiting off this pin, no local power source is needed for remote
sensing of temperature, and 2) the ROM may be read in absence of normal power.
In order for the DS18B20 to be able to perform accurate temperature conversions, sufficient power must
be provided over the DQ line when a temperature conversion is taking place. Since the operating current
of the DS18B20 is up to 1.5 mA, the DQ line will not have sufficient drive due to the 5k pullup resistor.
This problem is particularly acute if several DS18B20s are on the same DQ and attempting to convert
simultaneously.
There are two ways to assure that the DS18B20 has sufficient supply current during its active conversion
cycle. The first is to provide a strong pullup on the DQ line whenever temperature conversions or copies
to the E2 memory are taking place. This may be accomplished by using a MOSFET to pull the DQ line
directly to the power supply as shown in Figure 2. The DQ line must be switched over to the strong pull-
up within 10 µs maximum after issuing any protocol that involves copying to the E2 memory or initiates
temperature conversions. When using the parasite power mode, the VDD pin must be tied to ground.
Another method of supplying current to the DS18B20 is through the use of an external power supply tied
to the VDD pin, as shown in Figure 3. The advantage to this is that the strong pullup is not required on the
DQ line, and the bus master need not be tied up holding that line high during temperature conversions.
This allows other data traffic on the 1-Wire bus during the conversion time. In addition, any number of
DS18B20s may be placed on the 1-Wire bus, and if they all use external power, they may all
simultaneously perform temperature conversions by issuing the Skip ROM command and then issuing the
Convert T command. Note that as long as the external power supply is active, the GND pin may not be
floating.
The use of parasite power is not recommended above 100°C, since it may not be able to sustain
communications given the higher leakage currents the DS18B20 exhibits at these temperatures. For
applications in which such temperatures are likely, it is strongly recommended that VDD be applied to the
DS18B20.
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3Pages


DS18B20 電子部品, 半導体
DS18B20
64-BIT LASERED ROM
Each DS18B20 contains a unique ROM code that is 64-bits long. The first 8 bits are a 1-Wire family
code (DS18B20 code is 28h). The next 48 bits are a unique serial number. The last 8 bits are a CRC of
the first 56 bits. (See Figure 4.) The 64-bit ROM and ROM Function Control section allow the DS18B20
to operate as a 1-Wire device and follow the 1-Wire protocol detailed in the section “1-Wire Bus
System.” The functions required to control sections of the DS18B20 are not accessible until the ROM
function protocol has been satisfied. This protocol is described in the ROM function protocol flowchart
(Figure 5). The 1-Wire bus master must first provide one of five ROM function commands: 1) Read
ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm Search. After a ROM function
sequence has been successfully executed, the functions specific to the DS18B20 are accessible and the
bus master may then provide one of the six memory and control function commands.
CRC GENERATION
The DS18B20 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master
can compute a CRC value from the first 56-bits of the 64-bit ROM and compare it to the value stored
within the DS18B20 to determine if the ROM data has been received error-free by the bus master. The
equivalent polynomial function of this CRC is:
CRC = X8 + X5 + X4 + 1
The DS18B20 also generates an 8-bit CRC value using the same polynomial function shown above and
provides this value to the bus master to validate the transfer of data bytes. In each case where a CRC is
used for data transfer validation, the bus master must calculate a CRC value using the polynomial
function given above and compare the calculated value to either the 8-bit CRC value stored in the 64-bit
ROM portion of the DS18B20 (for ROM reads) or the 8-bit CRC value computed within the DS18B20
(which is read as a ninth byte when the scratchpad is read). The comparison of CRC values and decision
to continue with an operation are determined entirely by the bus master. There is no circuitry inside the
DS18B20 that prevents a command sequence from proceeding if the CRC stored in or calculated by the
DS18B20 does not match the value generated by the bus master.
The 1-Wire CRC can be generated using a polynomial generator consisting of a shift register and XOR
gates as shown in Figure 6. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is
available in Application Note 27 entitled “Understanding and Using Cyclic Redundancy Checks with
Dallas Semiconductor Touch Memory Products.”
The shift register bits are initialized to 0. Then starting with the least significant bit of the family code,
1 bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number is
entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC
value. Shifting in the 8 bits of CRC should return the shift register to all 0s.
64-BIT LASERED ROM Figure 4
8-BIT CRC CODE
48-BIT SERIAL NUMBER
8-BIT FAMILY CODE
(28h)
MSB
LSB MSB
LSB MSB
LSB
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共有リンク

Link :


部品番号部品説明メーカ
DS18B20

Programmable Resolution 1-Wire Digital Thermometer

Maxim Integrated Products
Maxim Integrated Products
DS18B20

Programmable Resolution 1-Wire Digital Thermometer

Dallas Semiconductor
Dallas Semiconductor
DS18B20-PAR

1-Wire Parasite-Power Digital Thermometer

Maxim Integrated Products
Maxim Integrated Products
DS18B20X

Flipchip 1-Wire Digital Thermometer

Dallas Semiconductor
Dallas Semiconductor


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