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### DS18B20 数字温度传感器技术解析 #### 一、概述 DS18B20是一款高性能数字温度传感器，由Dallas Semiconductor（现在是Maxim Integrated的一部分）制造。这款传感器采用独特的单线（1-Wire）通信协议，只需要通过一条数据线即可完成与微处理器的数据交换，极大地简化了系统设计并减少了外部组件的需求。DS18B20适用于多种温度测量应用场合，如工业控制、家用电器、环境监测等。 #### 二、主要特性 1. **独特的单线接口**：DS18B20仅需一条数据线（加上地线）进行通信，简化了分布式温度传感系统的布线复杂度。 2. **多路复用能力**：支持在同一总线上挂载多个DS18B20传感器，便于构建大规模的温度监测网络。 3. **无需外部组件**：集成电源管理功能，可直接从数据线获取工作所需电能，无需额外的电源电路。 4. **宽电压范围**：供电电压范围为3.0V至5.5V，适应性广泛。 5. **零待机功耗**：在待机状态下几乎不消耗任何电能，适合电池供电的应用场景。 6. **测量范围广**：可测量-55°C到+125°C的温度区间，转换为华氏度为-67°F到+257°F。 7. **高精度**：在-10°C到+85°C的范围内，测量精度可达±0.5°C。 8. **可编程分辨率**：温度分辨率可在9位至12位之间选择，满足不同应用场景的需求。 9. **快速转换时间**：将12位温度值转换为数字信号的时间不超过750毫秒。 10. **用户自定义报警设置**：可通过软件配置温度报警阈值，并且这些设置存储在非易失性内存中。 11. **报警搜索命令**：能够自动识别并定位那些超出设定温度范围的传感器。 #### 三、引脚说明 - **GND**：接地引脚。 - **DQ**：数据输入/输出引脚。对于单线操作而言，该引脚采用开漏设计。（参见“寄生电源”部分。） - **VDD**：电源引脚。如果使用寄生电源模式，则此引脚无需连接外部电源。 #### 四、应用领域 DS18B20数字温度传感器因其独特的特性和优势，在众多领域得到了广泛应用： 1. **恒温控制系统**：用于恒温器等恒温控制设备中，实现对温度的精确控制。 2. **工业系统**：在工业自动化领域，用于实时监测关键设备的工作温度，确保运行安全。 3. **消费产品**：集成于各种家用电器中，例如空调、冰箱等，提供智能化的温度管理功能。 4. **温度计**：作为专业温度计的核心部件，提供高精度的温度测量。 5. **热敏感系统**：广泛应用于对温度变化敏感的系统中，如化学反应过程监控、半导体制造等。 #### 五、封装形式 DS18B20提供两种封装形式： - **TO-92**：适用于空间受限或成本敏感的应用。 - **8-Pin SOIC (150mil)**：更适合需要较高可靠性和易于焊接的场合。 #### 六、结论 DS18B20以其独特的优势成为了数字温度传感器领域的佼佼者。其强大的功能、简单的接口以及广泛的适用性使其成为诸多工业和消费电子产品的理想选择。无论是对于初学者还是经验丰富的工程师来说，掌握DS18B20的工作原理和技术细节都是非常有价值的。

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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

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

- 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.

DS18B20

Programmable Resolution

1-Wire

Digital Thermomete

www.dalsemi.com

PRELIMINARY

DALLAS

DS1820

1 2 3

GND

VDD

1 2 3

BOTTOM VIEW

DS18B20 To-92

Package

GND

DS18B20Z

8-Pin SOIC (150 mil)

DS18B20

2 of 27

DETAILED PIN DESCRIPTION Table 1

8PIN SOIC

TO92 SYMBOL DESCRIPTION

5 1 GND Ground.

42DQData Input/Output pin. For 1-Wire operation: Open

drain. (See “Parasite Power” section.)

33V

Optional V

pin. See “Parasite Power” section for

details of connection. V

must be grounded for

operation in parasite power mode.

DS18B20Z (8-pin SOIC): All pins not specified in this table are not to be connected.

OVERVIEW

The block diagram of Figure 1 shows the major components of the DS18B20. The DS18B20 has four

main data components: 1) 64-bit lasered ROM, 2) temperature sensor, 3) nonvolatile temperature alarm

triggers TH and TL, and 4) a configuration register. The device derives its power from the 1-Wire

communication line by storing energy on an internal capacitor during periods of time when the signal line

is high and continues to operate off this power source during the low times of the 1-Wire line until it

returns high to replenish the parasite (capacitor) supply. As an alternative, the DS18B20 may also be

powered from an external 3 volt - 5.5 volt supply.

Communication to the DS18B20 is via a 1-Wire port. With the 1-Wire port, the memory and control

functions will not be available before the ROM function protocol has been established. The 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. These commands operate on the 64-bit lasered ROM portion of each

device and can single out a specific device if many are present on the 1-Wire line as well as indicate to

the bus master how many and what types of devices are present. After a ROM function sequence has

been successfully executed, the memory and control functions are accessible and the master may then

provide any one of the six memory and control function commands.

One control function command instructs the DS18B20 to perform a temperature measurement. The result

of this measurement will be placed in the DS18B20’s scratch-pad memory, and may be read by issuing a

memory function command which reads the contents of the scratchpad memory. The temperature alarm

triggers TH and TL consist of 1 byte EEPROM each. If the alarm search command is not applied to the

DS18B20, these registers may be used as general purpose user memory. The scratchpad also contains a

configuration byte to set the desired resolution of the temperature to digital conversion. Writing TH, TL,

and the configuration byte is done using a memory function command. Read access to these registers is

through the scratchpad. All data is read and written least significant bit first.

DS18B20

3 of 27

DS18B20 BLOCK DIAGRAM Figure 1

PARASITE POWER

The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power

whenever the DQ or V

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 E

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 E

memory or initiates

temperature conversions. When using the parasite power mode, the V

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 V

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 V

be applied to the

DS18B20.

64-BIT ROM

AND

1-WIRE PORT

MEMORY AND

CONTROL LOGIC

SCRATCHPAD

8-BIT CRC

ENERAT

TEMPERATURE SENSOR

HIGH TEMPERATURE

TRIGGER, TH

LOW TEMPERATURE

TRIGGER, TL

CONFIGURATION

POWER

SUPPLY

SENSE

INTERNAL V

DS18B20

5 of 27

OPERATION - MEASURING TEMPERATURE

The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the

DS18B20 is configurable (9, 10, 11, or 12 bits), with 12-bit readings the factory default state. This

equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C. Following the issuance of

the Convert T [44h] command, a temperature conversion is performed and the thermal data is stored in

the scratchpad memory in a 16-bit, sign-extended two’s complement format. The temperature

information can be retrieved over the 1-Wire interface by issuing a Read Scratchpad [BEh] command

once the conversion has been performed. The data is transferred over the 1-Wire bus, LSB first. The

MSB of the temperature register contains the “sign” (S) bit, denoting whether the temperature is positive

or negative.

Table 2 describes the exact relationship of output data to measured temperature. The table assumes 12-bit

resolution. If the DS18B20 is configured for a lower resolution, insignificant bits will contain zeros. For

Fahrenheit usage, a lookup table or conversion routine must be used.

Temperature/Data Relationships Table 2

-1

-2

-3

-4

LSB

MSb

(unit = °C)

LSb

SSSSS2

MSB

TEMPERATURE DIGITAL OUTPUT

(Binary)

DIGITAL

OUTPUT

(Hex)

+125°C 0000 0111 1101 0000 07D0h

+85°C 0000 0101 0101 0000 0550h*

+25.0625°C 0000 0001 1001 0001 0191h

+10.125°C 0000 0000 1010 0010 00A2h

+0.5°C 0000 0000 0000 1000 0008h

0°C 0000 0000 0000 0000 0000h

-0.5°C 1111 1111 1111 1000 FFF8h

-10.125°C 1111 1111 0101 1110 FF5Eh

-25.0625°C 1111 1110 0110 1111 FF6Fh

-55°C 1111 1100 1001 0000 FC90h

*The power on reset register value is +85°C.

OPERATION - ALARM SIGNALING

After the DS18B20 has performed a temperature conversion, the temperature value is compared to the

trigger values stored in TH and TL. Since these registers are 8-bit only, bits 9-12 are ignored for

comparison. The most significant bit of TH or TL directly corresponds to the sign bit of the 16-bit

temperature register. If the result of a temperature measurement is higher than TH or lower than TL, an

alarm flag inside the device is set. This flag is updated with every temperature measurement. As long as

the alarm flag is set, the DS18B20 will respond to the alarm search command. This allows many

DS18B20s to be connected in parallel doing simultaneous temperature measurements. If somewhere the

temperature exceeds the limits, the alarming device(s) can be identified and read immediately without

having to read non-alarming devices.

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