DS18B20温度传感器：1-Wire接口，独特特性

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"DS18B20.pdf是关于温度传感器DS18B20的数据手册，该手册详细介绍了DS18B20的功能特性和应用领域。" DS18B20是一款高度集成的温度传感器，它具有独特的1-Wire接口，只需要一个端口引脚即可实现通信，大大简化了硬件设计。每个DS18B20传感器都拥有一个唯一的64位序列代码，存储在非易失性ROM上，便于识别和管理多个传感器节点。这种多滴特性使得分布式温度传感应用变得非常便捷。传感器无需额外外部组件即可工作，电源电压范围为3.0V到5.5V，能够直接从数据线上获取电力。DS18B20可测量的温度范围为-55°C到+125°C，适用于各种环境条件。在-10°C至+85°C的范围内，其精度可达到±0.5°C，提供高度准确的温度读数。 DS18B20的分辨率可以由用户自定义，从9位到12位不等，允许用户根据具体需求调整测量精度。温度转换为12位数字词的时间最快只需750毫秒，确保了快速的响应速度。此外，DS18B20还支持用户定义的非挥发性（NV）报警设置，可以通过"报警搜索命令"来识别和定位那些温度超出预设范围的设备，这对于监控和报警系统尤其有用。 DS18B20传感器封装多样，包括8-pin SO（150mil）、8-pin μSOP和3-pin TO-92封装，适合不同应用场景。软件兼容性方面，DS18B20与DS1822保持一致，这意味着已有的DS1822软件平台可以直接用于DS18B20，降低了开发成本和复杂性。这款传感器在众多领域都有广泛的应用，如恒温控制器、工业系统、消费产品、温度计，以及任何对温度敏感的系统。DS18B20以其高精度、易用性和灵活性，在温度测量解决方案中占据了一席之地。

DS18B20

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OPERATION — ALARM SIGNALING

After the DS18B20 performs a temperature conversion, the temperature value is compared to the user-

defined two’s complement alarm trigger values stored in the 1-byte T

and T

registers (see Figure 3).

The sign bit (S)

indicates if the value is positive or negative: for positive numbers S = 0 and for negative

numbers S = 1. The T

and T

registers are nonvolatile (EEPROM) so they will retain data when the

device is powered down. T

and T

can be accessed through bytes 2 and 3 of the scratchpad as explained

in the MEMORY section of this datasheet.

AND T

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

S 2

Only bits 11 through 4 of the temperature register are used in the T

and T

comparison since T

and T

are 8-bit registers. If the measured temperature is lower than or equal to T

or higher than or equal to T

an alarm condition exists and an alarm flag is set inside the DS18B20. This flag is updated after every

temperature measurement; therefore, if the alarm condition goes away, the flag will be turned off after the

next temperature conversion.

The master device can check the alarm flag status of all DS18B20s on the bus by issuing an Alarm Search

[ECh] command. Any DS18B20s with a set alarm flag will respond to the command, so the master can

determine exactly which DS18B20s have experienced an alarm condition. If an alarm condition exists

and the T

or T

settings have changed, another temperature conversion should be done to validate the

alarm condition.

POWERING THE DS18B20

The DS18B20 can be powered by an external supply on the V

pin, or it can operate in “parasite power”

mode, which allows the DS18B20 to function without a local external supply. Parasite power is very

useful for applications that require remote temperature sensing or that are very space constrained. Figure

1 shows the DS18B20’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via

the DQ pin when the bus is high. The stolen charge powers the DS18B20 while the bus is high, and some

of the charge is stored on the parasite power capacitor (C

) to provide power when the bus is low. When

the DS18B20 is used in parasite power mode, the V

pin must be connected to ground.

In parasite power mode, the 1-Wire bus and C

can provide sufficient current to the DS18B20 for most

operations as long as the specified timing and voltage requirements are met (refer to the DC

ELECTRICAL CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this data

sheet). However, when the DS18B20 is performing temperature conversions or copying data from the

scratchpad memory to EEPROM, the operating current can be as high as 1.5mA. This current can cause

an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be

supplied by C

. To assure that the DS18B20 has sufficient supply current, it is necessary to provide a

strong pullup on the 1-Wire bus whenever temperature conversions are taking place or data is being

copied from the scratchpad to EEPROM. This can be accomplished by using a MOSFET to pull the bus

directly to the rail as shown in Figure 4. The 1-Wire bus must be switched to the strong pullup within

10μs (max) after a Convert T [44h] or Copy Scratchpad [48h] command is issued, and the bus must be

held high by the pullup for the duration of the conversion (t

conv

) or data transfer (t

= 10ms). No other

activity can take place on the 1-Wire bus while the pullup is enabled.

The DS18B20 can also be powered by the conventional method of connecting an external power supply

to the V

pin, as shown in Figure 5. The advantage of this method is that the MOSFET pullup is not

required, and the 1-Wire bus is free to carry other traffic during the temperature conversion time.

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