Datasheet

ManualsBrandsSENSIRION ManualsSensors1-100738-01

www.sensirion.com Version 4 – May 2014 1/14

Datasheet SHT21

Humidity and Temperature Sensor IC

 Fully calibrated

 Digital output, I

C interface

 Low power consumption

 Excellent long-term stability

 DFN type package – reflow solderable

Dimensions

Figure 1: Drawing of SHT21 sensor package, dimensions are

given in mm (1mm = 0.039inch), tolerances are ±0.1mm. The

die pad (center pad) is internally connected to VSS. The NC

pads must be left floating. VSS = GND, SDA = DATA.

Numbering of E/O pads starts at lower right corner (indicated by

notch in die pad) and goes clockwise (compare Table 2).

Sensor Chip

SHT21 features a generation 4C CMOSens® chip.

Besides the capacitive relative humidity sensor and the

band gap temperature sensor, the chip contains an

amplifier, A/D converter, OTP memory and a digital

processing unit.

Material Contents

While the sensor itself is made of Silicon the sensors’

housing consists of a plated Cu lead-frame and green

epoxy-based mold compound. The device is fully RoHS

and WEEE compliant, e.g. free of Pb, Cd and Hg.

Additional Information and Evaluation Kits

Additional information such as Application Notes is

available from the web page www.sensirion.com/sht21.

For more information please contact Sensirion via

info@sensirion.com.

For SHT2x two Evaluation Kits are available: EK-H4, a

four-channel device with Viewer Software, that also serves

for data-logging, and a simple EK-H5 directly connecting

one sensor via USB port to a computer.

1.0

2.4

0.3

0.4

1.5

0.4

0.75

1.1

0.2

SCL

SDA

VSS

VDD

Bottom

View

SHT21

D0AC4

3.0

2.2

1.4 max

3.0

0.3 typ

2.4 max

Product Summary

The SHT21 humidity and temperature sensor of Sensirion

has become an industry standard in terms of form factor

and intelligence: Embedded in a reflow solderable Dual

Flat No leads (DFN) package of 3 x 3mm foot print and

1.1mm height it provides calibrated, linearized sensor

signals in digital, I

C format.

The SHT2x sensors contain a capacitive type humidity

sensor, a band gap temperature sensor and specialized

analog and digital integrated circuit – all on a single

CMOSens

chip. This yields in an unmatched sensor

performance in terms of accuracy and stability as well as

minimal power consumption.

Every sensor is individually calibrated and tested. Lot

identification is printed on the sensor and an electronic

identification code is stored on the chip – which can be

read out by command. Furthermore, the resolution of

SHT2x can be changed by command (8/12bit up to

12/14bit for RH/T) and a checksum helps to improve

communication reliability.

With this set of features and the proven reliability and

long-term stability, the SHT2x sensors offer an

outstanding performance-to-price ratio. For testing SHT2x

two evaluation kits EK-H4 and EK-H5 are available.

Summary of content (14 pages)

PAGE 1
Datasheet SHT21 Humidity and Temperature Sensor IC      Fully calibrated Digital output, I2C interface Low power consumption Excellent long-term stability DFN type package – reflow solderable Product Summary The SHT21 humidity and temperature sensor of Sensirion has become an industry standard in terms of form factor and intelligence: Embedded in a reflow solderable Dual Flat No leads (DFN) package of 3 x 3mm foot print and 1.
PAGE 2
Sensor Performance Relative Humidity1234 Parameter Temperature567 Condition 12 bit 8 bit Value 0.04 0.7 Units %RH %RH typ 2 see Figure 2 %RH Repeatability 0.1 %RH Repeatability Hysteresis 1 <0.1 %RH Resolution 1 Accuracy tolerance 2 max Condition 14 bit 12 bit Value 0.01 0.04 Units °C °C typ °C max 0.3 see Figure 3 °C Operating Range extended 4 0.1 -40 to 125 %RH Response Time 7 s 8 s Long Term Drift  63% Typ. 5 to 30 8 < 0.02 °C/yr 0 to 100 < 0.
PAGE 3
Users Guide SHT21 For details on how Sensirion is specifying and testing accuracy performance please consult Application Note “Statement on Sensor Specification”. Relative Humidity (%) 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).
PAGE 4
Datasheet SHT21 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 overmolding 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 lands9 should be 0.2mm longer than the package I/O pads.
PAGE 5
Datasheet SHT21 recommended to further process the sensors within 1 year after date of delivery. It is of great importance to understand that a humidity sensor is not a normal electronic component and needs to be handled with care. Chemical vapors at high concentration in combination with long exposure times may offset the sensor reading.
PAGE 6
Datasheet SHT21 of MCUs. See Table 4 and Table 5 for detailed I/O characteristic of the sensor. 3 Interface Specifications Pin Name Comment 1 SDA Serial Data, bidirectional 4 2 VSS Ground 5 5 VDD Supply Voltage 6 SCL Serial Clock, bidirectional 6 3,4 NC Not Connected 4 Electrical Characteristics 3 2 1 Table 2 SHT2x pin assignment, NC remain floating (top view) 3.1 Power Pins (VDD, VSS) The supply voltage of SHT2x must be in the range of 2.1 – 3.6V, recommended supply voltage is 3.0V.
PAGE 7
Datasheet SHT21 5.1 1/fSCL tSCLH tR tSCLL 70% SCL 30% tSU SDA valid write tHD DATA IN 70% SDA 30% SDA valid read tR tF tVD DATA OUT 70% SDA 30% Figure 12 Timing Diagram for Digital Input/Output Pads, abbreviations are explained in Table 5. SDA directions are seen from the sensor. Bold SDA line is controlled by the sensor, plain SDA line is controlled by the micro-controller. Note that SDA valid read time is triggered by falling edge of anterior toggle.
PAGE 8
Datasheet SHT21 In the hold master mode, the SHT2x pulls down the SCL line while measuring to force the master into a wait state. By releasing the SCL line the sensor indicates that internal processing is terminated and that transmission may be continued. 3 4 5 6 7 8 S 1 0 0 0 0 0 0 0 9 1 1 1 0 0 1 0 1 I2C address + write ACK Measurement Hold during measurement ACK ACK 0 1 0 1 0 0 1 0 Data (MSB) Data (LSB) Stat.
PAGE 9
Datasheet SHT21 Please note: I2C communication allows for repeated Start conditions (S) without closing prior sequence with Stop condition (P) – compare Figures 15, 16 and 18. Still, any sequence with adjacent Start condition may alternatively be closed with a Stop condition. 5.5 Soft Reset This command (see Table 6) is used for rebooting the sensor system without switching the power off and on again.
PAGE 10
Datasheet SHT21 5.8 Serial Number SHT21 provides an electronic identification code. For instructions on how to read the identification code please refer to the Application Note “Electronic Identification Code” – to be downloaded from the web page www.sensirion.com/SHT21. 6 Conversion of Signal Output Default resolution is set to 12 bit relative humidity and 14 bit temperature reading. Measured data are transferred in two byte packages, i.e.
PAGE 11
Datasheet SHT21 frame at diced edge is not covered with respective protective coating. The total weight of the sensor is 25mg. 8.3 Traceability Information All SHT2x are laser marked with an alphanumeric, fivedigit code on the sensor – see Figure 19. The marking on the sensor consists of two lines with five digits each. The first line denotes the sensor type (SHT21). The first digit of the second line defines the output mode (D = digital, Sensibus and I2C, P = PWM, S = SDM).
PAGE 12
Datasheet SHT21 Please note that even if SHT1x/7x protocol is applied the timing values of Table 5 and Table 7 in this SHT2x datasheet apply. For the calculation of physical values the following equation must be applied: For relative humidity RH RH   6  125  SRH 2 RES and for temperature T T   46.85  175.72  ST 2 RES RES is the chosen respective resolution, e.g. 12 (12bit) for relative humidity and 14 (14bit) for temperature. www.sensirion.
PAGE 13
Datasheet SHT21 Revision History Date 6 May 2009 21 January 2010 5 May 2010 Version 0.3 1.0 1.1 9 May 2011 2 December 2011 3 May 2014 4 www.sensirion.com Page(s) 1–9 1 – 4, 7 – 10 1 – 12 Changes Initial preliminary release Complete revision. For complete revision list please require respective document. Typical specification for temperature sensor. Elimination of errors. For detailed information, please require complete change list at info@sensirion.com.
PAGE 14
Datasheet SHT21 Warning, Personal Injury Important Notices Do not use this product as safety or emergency stop devices or in any other application where failure of the product could result in personal injury. Do not use this product for applications other than its intended and authorized use. Before installing, handling, using or servicing this product, please consult the data sheet and application notes. Failure to comply with these instructions could result in death or serious injury.