DS18B20温度传感器详解

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"DS18B20 是一种数字温度传感器，由 Dallas Semiconductor（现 Maxim Integrated）制造。这款传感器以其独特的1-Wire 接口而知名，只需一个端口引脚即可实现通信，大大简化了硬件连接。每个DS18B20 设备都拥有一个唯一的64位序列代码，存储在芯片上的非易失性ROM 中，这使得在同一系统中可以轻松地识别和管理多个传感器。 DS18B20 具有多滴功能，非常适合分布式温度传感应用。它不需要外部组件，电源电压范围在3.0V到5.5V之间，并且可以从数据线上获取电源。这款传感器能够测量-55°C到+125°C之间的温度，具有较高的精度，在-10°C到+85°C范围内精度可达±0.5°C。温度分辨率可由用户选择，范围为9至12位，这意味着它可以提供非常精细的温度读数。转换温度至12位数字词的时间最大为750毫秒，提供了快速的温度更新能力。DS18B20 还支持用户定义的非挥发性报警设置，当温度超出预设范围时，可以通过报警搜索命令来识别和寻址这些设备。这使得它在温度报警条件下的应用非常灵活，如在温控系统、工业设备、消费产品、温度计以及任何对温度敏感的系统中都有广泛的应用。 DS18B20 提供三种封装选项：8引脚SO（150mil）、8引脚μSOP 和3引脚TO-92。此外，其软件兼容DS1822，这意味着如果你熟悉DS1822，使用DS18B20 将更加得心应手。总结来说，DS18B20 是一种高效、高精度、易于集成的数字温度传感器，尤其适用于需要多点温度监控的场合。其独特的特性，如1-Wire 接口、内部电源管理和报警功能，使其成为各种温度监测应用的理想选择。" 这篇摘要详细介绍了DS18B20 温度传感器的主要特点、功能、性能参数以及封装形式，涵盖了从硬件连接、通信方式到软件兼容性和应用场景等多个方面，有助于读者深入理解并有效利用这款芯片。

DS18B20

5 of 21

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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