DS18B20数字温度计：1-wire接口与独特特性

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"DS18B20英文手册是一份详细的技术文档，涵盖了DS18B20数字温度计的特性、引脚分配、工作原理和应用领域。" DS18B20是一款由Maxim Integrated制造的数字温度传感器，其主要特点包括： 1. **独特的1-Wire接口**：只需一个端口引脚即可实现通信，极大地简化了硬件设计，减少了电路板空间的占用。 2. **唯一的64位序列码**：每个DS18B20设备都拥有独一无二的序列号，存储在非易失性ROM中，方便在多设备系统中进行区分和管理。 3. **多滴落能力**：支持分布式温度传感应用，可以连接多个DS18B20在同一总线上，实现温度的分布式监测。 4. **无需外部组件**：设计简洁，无需额外的电容或电阻等外部元件，降低了使用成本。 5. **电源范围广泛**：可在3.0V至5.5V的电压范围内工作，可直接从数据线获取电源。 6. **宽温度测量范围**：能够测量从-55°C到+125°C（-67°F到+257°F）的温度，适用于各种环境条件。 7. **高精度**：在-10°C到+85°C的范围内，精度可达±0.5°C，确保了温度读取的准确性。 8. **可调整分辨率**：用户可以根据需求选择9到12位的分辨率，以满足不同应用场景对温度测量精度的需求。 9. **快速转换时间**：能够在750毫秒内将温度转换为12位数字值，提高了实时性。 10. **用户定义的非挥发性报警设置**：允许用户设定温度报警阈值，当温度超出设定范围时，会触发报警信号。 11. **报警搜索命令**：通过此命令可以快速识别并定位温度超出设定限制的设备，便于系统监控和故障排查。 12. **软件兼容性**：与DS1822保持软件兼容，方便已使用DS1822的系统进行升级或扩展。 DS18B20的引脚分配如下： - GND：接地 - DQ：数据输入/输出，既是数据传输线也是电源线 - VDD：电源电压 - NC：无连接，表示该引脚不需连接任何电路这款传感器广泛应用于恒温控制、工业系统、消费产品、温度计以及任何对温度敏感的系统中。其高集成度、易用性和精确度使其成为许多温度监测和控制应用的理想选择。

DS18B20

4 of 20

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 result of a temperature measurement is higher than T

or lower than 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 1.5 mA. 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 10

µs (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

= 10 ms). 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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