SHT21温湿度传感器：全校准，I2C接口，长期稳定性优秀
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"SHT21是一款高精度的温湿度传感器，具有全校准、数字输出（I2C接口）、低功耗、长期稳定性优异等特点。该传感器采用DFN封装，中心焊盘内部连接至VSS（GND）。SHT21的核心是第4代CMOSens®芯片，集成了电容式相对湿度传感器、带隙温度传感器、放大器、A/D转换器、OTP内存和数字处理单元。传感器的外壳由镀铜铅框架和绿色环氧基模塑化合物制成，符合RoHS和WEEE标准，不含铅、镉和汞。用户可以访问www.sensirion.com/sht21获取更多应用笔记等信息，或通过info@sensirion.com联系Sensirion获取详细评估套件和技术支持。"
SHT21温湿度传感器是Sensirion公司推出的一款高性能传感器，它在工业、农业、医疗、智能家居等多个领域有广泛应用。该传感器的主要特点包括：
1. **全校准**：SHT21出厂时已经进行了全面校准，用户无需额外的校准步骤即可直接使用，提高了测量的准确性和一致性。
2. **数字输出，I2C接口**：通过I2C接口，SHT21能够与微控制器或其他系统轻松通信，实现数据的高速传输，并减少了所需的外部硬件。
3. **低功耗设计**：这使得SHT21适用于电池供电或能源有限的环境，如物联网设备和移动设备。
4. **长期稳定性**：SHT21的传感器性能在长时间内保持稳定，减少了因时间推移导致的测量误差。
5. **封装形式**：采用DFN封装，这种小型化设计便于集成到各种紧凑型设备中，同时中心焊盘连接至VSS（接地），简化了电路设计。
6. **材料和环保**：传感器主体由硅制成，外壳材料符合RoHS和WEEE标准，确保了环保要求。
7. **功能集成**：SHT21的CMOSens®芯片集成了多种功能，包括湿度和温度传感器、放大器、A/D转换器、OTP内存和数字处理单元，实现了高集成度和高效能。
8. **附加资源**：Sensirion公司提供了丰富的附加信息，如应用笔记和评估套件，帮助开发者更好地理解和应用SHT21。
在实际应用中，SHT21可广泛用于室内空气质量监测、温室环境控制、人体舒适度检测、医疗设备和数据中心环境监控等领域。其高精度和稳定性使其成为许多需要精确温湿度数据的场合的理想选择。用户可以通过官方网站或直接联系厂家获取技术支持，进一步优化其在具体应用中的性能表现。
Datasheet SHT21
www.sensirion.com Version 1.0 – January 2010 3/12
Users Guide SHT2x
1 Extended Specifications
1.1 Operating Range
The sensor works stable within recommended Normal
Range – see Figure 4. Long term exposure to conditions
outside Normal Range, especially at humidity >80%RH,
may temporarily offset the RH signal (+3%RH after 60h).
After return into the Normal Range it will slowly return
towards calibration state by itself. See Section 2.3 “Recon-
ditioning Procedure” for eliminating the offset. Prolonged
exposure to extreme conditions may accelerate ageing.
Figure 4 Operating Conditions
1.2 RH accuracy at various temperatures
Maximal tolerance for RH accuracy at 25°C is defined in
Figure 2. For other temperatures maximal tolerance has
been evaluated to be within limits displayed in Figure 5
8
.
100
±5
90
±6
±5
±4
±5 ±7 ±8
80
70
60
50
40
30
±4 ±3 ±3
±3 ±4 ±6
20
10
±6 ±5
±4
±5
Relative Humidity (%RH)
0
±5
±7
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
Temperature (°C)
Figure 5 Maximal tolerance of relative humidity measurements
given in %RH for temperatures 0 – 80°C.
Please note that above values are maximal tolerances (not
including hysteresis) against a high precision reference
such as a dew point mirror. Typical deviations are at
±2%RH where maximal tolerance is ±3%RH and about
half the maximal tolerance at other values.
8
Details on how Sensirion is specifying and testing accuracy performance are
planned to be published on the Sensirion web page.
2 Application Information
2.1 Soldering Instructions
The DFN’s die pad (centre pad) and perimeter I/O pads
are fabricated from a planar copper lead-frame by over-
molding leaving the die pad and I/O pads exposed for
mechanical and electrical connection. Both the I/O pads
and die pad should be soldered to the PCB. In order to
prevent oxidation and optimize soldering, the bottom side
of the sensor pads is plated with Ni/Pd/Au.
On the PCB the I/O lands
9
should be 0.2mm longer than
the package I/O pads. Inward corners may be rounded to
match the I/O pad shape. The I/O land width should match
the DFN-package I/O-pads width 1:1 and the land for the
die pad should match 1:1 with the DFN package – see
Figure 6.
The solder mask
10
design for the land pattern preferably is
of type Non-Solder Mask Defined (NSMD) with solder
mask openings larger than metal pads. For NSMD pads,
the solder mask opening should be about 120µm to
150µm larger than the pad size, providing a 60µm to 75µm
design clearance between the copper pad and solder
mask. Rounded portions of package pads should have a
matching rounded solder mask-opening shape to minimize
the risk of solder bridging. For the actual pad dimensions,
each pad on the PCB should have its own solder mask
opening with a web of solder mask between adjacent
pads.
Figure 6 Recommended metal land pattern for SHT2x. Values
in mm. Die pad (centre pad) and NC pads may be left floating or
be connected to ground. The outer dotted line represents the
outer dimension of the DFN package.
For solder paste printing a laser-cut, stainless steel stencil
with electro-polished trapezoidal walls and with 0.125mm
stencil thickness is recommended. For the I/O pads the
stencil apertures should be 0.1mm longer than PCB pads
and positioned with 0.1mm offset away from the centre of
9
The land pattern is understood to be the metal layer on the PCB, onto which
the DFN pads are soldered to.
10
The solder mask is understood to be the insulating layer on top of the PCB
covering the connecting lines.
0
20
40
60
80
100
-40 -20 0 20 40 60 80 100 120
Temperature (°C)
Relative Humidity (%)
Max.
Range
Normal
Range
1.0
1.0
0.3
0.4
1.6
0.4
0.7
0.2
0.2
2.4
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