SHT21

SHT21 SENSIRION | Alldatasheet

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www.sensirion.com Version 5 – October 2022 1/14 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 Dimensions Figure 1: Drawing of SHT21 sensor package, dimensions are given in mm (1 mm = 0.039 inch), tolerances are ±0.1 mm. The die pad (center pad) is internally connected to VSS. The NC pads must be left floating . VSS = GND, S DA = 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 feature s a generation 4C CMOSe ns® chip. Besides the capacitive r elative 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 senso rs’ housing consists of a plated C u 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 1.0 2.4 0.3 0.4 1.5 0.4 0.75 1.1 0.2 SCL SDA NC NC 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 1.1 mm height it provides calibrated, linearized sensor signals in digital, I2C format. The SHT2x sensors contain a capacitive type humidity sensor, a band gap temperature sensor and specialized analog an d digital integra ted 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 e lectronic identification code is stored on the chip – which can be read out by command. Furthermore, the resolution of SHT2x can be changed b y com mand (8/12 bit up to 12/14 bit 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.

www.sensirion.com Version 5 – October 2022 2/14 Sensor Performance Relative Humidity1234 Parameter Condition Value Units Resolution 1 12 bit 0.04 %RH 8 bit 0.7 %RH Accuracy tolerance 2 typ 2 %RH max see Figure 2 %RH Repeatability 0.1 %RH Hysteresis 1 %RH Nonlinearity <0.1 %RH Response time 3  63% 8 s Operating Range extended 4 0 to 100 %RH Long Term Drift 5 Typ. < 0.25 %RH/yr ± 0 ± 2 ± 4 ± 6 ± 8 ± 10 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity (%RH) DRH (%RH) maximum accuracy typical accuracy Figure 2 Typical and m aximal tolerance at 25°C f or relative humidity. For extensive information see Users Guide, Sect. 1.2. Electrical Specification Parameter Condition min typ max Units Supply Voltage, VDD 2.1 3.0 3.6 V Supply Current, IDD 6 sleep mode 0.15 0.4 µA measuring 200 300 330 µA Power Dissipation 6 sleep mode 0.5 1.2 µW measuring 0.6 0.9 1.0 mW average 8bit 3.2 µW Heater VDD = 3.0 V 5.5mW, DT = + 0.5-1.5°C Communication digital 2-wire interface, I2C protocol Table 1 Electrical specification. For absolute maximum values see Section 4.1 of Users Guide. 1 Default measurement resolutio n is 14 bit (temperature) / 12 bit (humidity). It can be reduced to 12/8 bit, 11/11 bit or 13/10 bit by command to user register. 2 Accuracies are tested at Outgoing Quality Control at 25°C and 3.0 V. Values exclude hysteresis and long term drift and are a pplicable to non -condensing environments only. 3 Time for achieving 63% of a step function, valid at 25°C and 1 m/s airflow.

4 Normal operating range: 0 -80 %RH, beyond this limit sensor may read a

reversible offset with slow kinetics (+3 %RH after 60 h at humidity >80 %RH). For more details please see Section 1.1 of the Users Guide. Temperature567 Parameter Condition Value Units Resolution 1 14 bit 0.01 °C 12 bit 0.04 °C Accuracy tolerance 2 typ 0.3 °C max see Figure 3 Repeatability 0.1 °C Operating Range extended 4 -40 to 125 °C Response Time 7  63% 5 to 30 s Long Term Drift 8 Typ. < 0.02 °C/yr ± 0.0 ± 0.5 ± 1.0 ± 1.5 ± 2.0 -40 -20 0 20 40 60 80 100 120 Temperature (°C) DT (°C) maximum accuracy typical accuracy Figure 3 Typical and maximal tolerance for temperature sensor in °C. Packaging Information Sensor Type Packaging Quantity Order Number SHT21 Tape & Reel 400 1-100707-01 Tape & Reel 1500 1-100645-01 Tape & Reel 5000 1-100694-01 Please Note: This datasheet is subject to change and may be amended without prior notice 5 Typical value for operation in normal RH/T operating range. Max. value is < 0.5 %RH/y. Value may be higher in environments with vaporized solvents , out- gassing tapes, adhesives, packaging materials, etc. For more details please refer to Handling Instructions.

6 Min and max values of Supply Current and Power Dissipation are based on

fixed VDD = 3.0 V and T<60°C. The average value is based on one 8bit measurement per second. 7 Response time depends on heat conductivity of sensor substrate. 8 Max. value is < 0.04°C/y.

www.sensirion.com Version 5 – October 2022 3/14 Users Guide SHT21

1 Extended Specification

For details on how Sensirion is specifying and testing accuracy performance please consult Application N ote “Statement on Sensor Specification”.

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 >8 0 %RH, may temporarily offset the RH signal (+3 %RH after 60 h). After return into the Normal R ange it will slowly return towards calibration state by itself. Prolonged exposure to extreme conditions may accelerate ageing. Figure 4 Operating Conditions

1.2 RH accuracy at various temperatures

Typical RH accuracy at 25°C is d efined in Figure 2. For other temperatures, typical accuracy has been evaluated to be as displayed in Figure 5. 0 10 20 30 40 50 60 70 80 Relative Humidity [%RH] Temperature [°C] Figure 5 Typical accuracy of relative humidity measurements given in %RH for temperatures 0 – 80°C.

1.3 Electrical Specification

Current consumption as given in Table 1 is dependent on temperature and supply voltage VDD. For estima tions on energy consumption of the sensor Figures 6 and 7 may be consulted. Please note that values given in these Figures are of typical nature and the variance is considerable. 0 20 40 60 80 100 120 Temperature (°C) Supply Current IDD (μA) Figure 6 Typical dep endency o f supply curren t (sleep mode) versus temperature at VDD = 3.0 V. Please note that the variance of these data can be above ±25% of displayed value. Supply Voltage (VDD) Supply Current IDD (nA) Figure 7 Typical dependency of supply curren t (sleep mode) versus supply voltage at 25°C. Please note that deviations may be up to ±50% of displayed value . Values at 60°C scale with a factor of about 15 (compare Table 1). 100 -40 -20 0 20 40 60 80 100 120 Temperature (°C) Relative Humidity (%) Max. Range Normal Range

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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 t he I/O lands9 should be 0.2 mm 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 8. The solder mask10 design for the land pattern preferably is of type Non -Solder Mask Def ined (NSMD) with solder mask openings larger than metal pads. For NSMD pads, the solder mask opening should be about 120 μm to 150 μm larger than the pad size, providing a 60 μm to 75 μm 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 8 Recommended metal land pattern for SHT2x. Values in mm. Die pad (centre pad) may be left floating or be connected to ground , NC pads shall be left floating . 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 0.125 mm stencil thickness is recommended . For the I/O pads the stencil apertures should be 0.1 mm longer than PCB pads and positioned with 0.1 mm offset away from the centre of the package. The die pad aperture should cover about 70 – 90% of the pad area – say up to 1.4 mm x 2.3 mm

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 understo od to be the insulating layer on top of the PCB

covering the connecting lines. centered on the thermal land area. It c an also be split in two openings. Due to th e low mo unted height of the DFN, “ no clean” type 3 solder paste11 is recommended as well as N itrogen purge during reflow. Figure 9 Soldering profile according to JEDEC standard. T P <= 260°C and t P < 30 sec for Pb-free assembly. TL < 220°C and t L < 150sec. Ramp-up/down speeds shall be < 5°C/sec. It is important to note that the diced edge or side faces of the I/O pads may oxidise over time, therefore a solder fillet may or may not form. Hence there is no guarantee for solder joint fillet heights of any kind. For soldering SHT2x, standard reflow soldering ovens may be used. The sensor is qualified to withstand soldering profile according to IPC/JEDEC J -STD-020 with peak temperatures at 260°C during up to 30 sec for Pb-free assembly in IR/Convection reflow ovens (see Figure 9). For manual soldering contact time must be limited to 5 seconds at up to 350°C. Immediately after the exposure to high temperatures th e sensor may te mporarily read a negative humidity offset (typ. -1 to -2 %RH after reflow soldering). This offset slowly disappears again by itself when the sensor is exposed to ambient conditions (typ. within 1-3 days). If RH testing is performed immediate ly after reflow soldering, this offset should be considered when defining the test limits. In no case, neither after manual nor reflow soldering, a board wash shall be applied. Therefore, and as mentioned above, it is strongly recommended to use “no-clean” solder paste. In case of appl ications with exposure of the sensor to corrosive gases or condensed water (i.e. environments with high relative humidity) the soldering pads shal l be sealed (e.g. conformal coating) to prevent loose contacts or short cuts.

11 Solder types are related to the solder particle size in the paste: Type 3 covers

the size range of 25 – 45 µm (powder type 42). 1.0 1.0 0.3 0.4 1.5 0.4 0.7 0.2 0.2 2.4 Temperature Time tP TP TL TS (max) tL preheating critical zone

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2.2 Storage Conditions and Handling Instructions

Moisture Sensitivity Level (MSL) is 1, acc ording to IPC/JEDEC J -STD-020. At the same time, it is recommended to further process the sensors within 1 year after date of delivery. It is of great importance to understand that a hu midity sensor is not a normal electronic component and needs to be handled with care. Chemical vapors at high concentration in combination with long exposure time s may offset the sensor reading. For this reason it is recommended to store the sensors in original packaging including the sealed ESD bag at following conditions: Temperature shall be in the range of 10°C – 50°C and humidity at 20 – 60%RH (sensors that are not stored in ESD bags). For sensors that have been removed from the original packaging we recommend to store them in ESD bags made of metal-in PE-HD12. In manufacturing and transport the sensors shall be prevented of high concentration of chemical solve nts and long exposure times. Out-gassing of glues, adhesive tapes and stickers or out -gassing packaging materi al such as bubble foils, foams, etc. shall be avoided. Manufacturing area shall be well ventilated. For more detailed information please consult t he document “Handling Instructions” [1] or contact Sensirion.

2.3 Temperature Effects

Relative hum idity reading strong ly depends on temperature. Therefore, it is essential to keep humidity sensors at the same temperature as the ai r of which the relative humidity is to be measured. In case of testing or qualification the reference sensor and test sensor must show equal tem perature to allow for comparing humidity readings. If the sensor shares a PCB with electronic components that pr oduce heat it should be mounted in a way that prevents heat transfer or keeps it as low as possible. Measures to reduce heat transfer can be ven tilation, reduction of copper layers between the sensor and the rest of the PCB or milling a slit into the PCB a round the sensor – see Figure 10. Furthermore, there are self -heating effects in c ase the measurement frequency is too high. To keep self -heating below 0.1°C, SHT2x should not be active for more than 10% of the time – e.g. maximum two measurements per second at 12 bit accuracy shall be made. 12 For example, 3M antistatic bag, product “1910” with zipper. Figure 10 Top view of example of mounted SHT2x with slits milled into PCB to minimize heat transfer.

2.4 Light

The SHT2x is not light sensitive. Prolonged direct exposure to sunshine or strong UV radiation may age the sensor.

2.5 Materials Used for Sealing / Mounting

Many materials absorb humidity and will act as a buffer increasing response times and hysteresis. Materials in the vicinity of the sensor must therefore be carefully chosen. Recommended materials are: Any metals, LC P, POM (Delrin), PTFE (Teflon), PEEK, PP, PB, PPS, PSU, PVDF, PVF. For sealing and gluing (use sparingly): Use high fille d epoxy for electronic packaging (e.g. glob top, underfill), and Silicone. Out -gassing of these material s may also contaminate the sensor (see Section 2.2). Therefore try to add the sensor as a last manufacturing step to the assembly, store the assembly we ll ventilated after manufacturing or bake at >50°C for 24 h to outgas contaminants before packing.

2.6 Wiring Considerations and Signal Integrity

Carrying the SCL and SDA signal parallel and in close proximity (e.g. in wires) for more than 10 cm may result in cross talk and loss of communication. This may be resolved by routing VDD and/or VSS between the two SDA signals and/or using shielded cables. Furt hermore, slowing down SCL frequency will possibly improve signal integrity. Power supply pins (VDD, VSS ) must be decoupled with a 100 nF capacitor – see Section 3.

3 Interface Specifications

1 SDA Serial Data, bidirectional

2 VSS Ground

5 VDD Supply Voltage

6 SCL Serial Clock, bidirectional

3.1 Power Pins (VDD, VSS)

as close to the sensor as possible – see Figure 11.

3.2 Serial clock (SCL)

3.3 Serial SDA (SDA)

low and remains valid until the next falling edge of SCL. RP and decoupling of VDD and VSS by a capacitor. resistors (e.g. 10 kΩ), are required to pull the signal high. characteristic of the sensor.

4 Electrical Characteristics

4.1 Absolute Maximum Ratings

Table 1. The absolute maximum ratings as given in Table 3 are stress ratings only and give additional info rmation. reliability (e.g. hot carrier degradation, oxide breakdown).

4.2 Input / Output Characteristics

strictly within the limits given in Table 4 & 5 and Figure 12. 2.1 V to 3.6 V, T = -40°C to 125°C, unless otherwise noted.

www.sensirion.com / D1 Version 5 – October 2022 7/14 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. Parameter min typ max Units SCL frequency, fSCL 0 - 0.4 MHz SCL High Time, tSCLH 0.6 - - µs SCL Low Time, tSCLL 1.3 - - µs SDA Set-Up Time, tSU 100 - - ns SDA Hold Time, tHD 0 - 900 ns SDA Valid Time, tVD 0 - 400 ns SCL/SDA Fall Time, tF 0 - 100 ns SCL/SDA Rise Time, tR 0 - 300 ns Capacitive Load on Bus Line, CB 0 - 400 pF Table 5 Timing specifications of digital input/output pads for I2C fast mo de. Entities are displayed in Figure 12. VDD = 2. 1 V to 3.6 V, T = -40°C to 125°C, unless otherwise noted.

5 Communication with Sensor

SHT21 communicates with I2C protocol. For information on I2C beyond the info rmation in the following Sections please look for the NXP I 2C-bus specifications and user manual. Please note that all sensors are set to the same I 2C address, as defined in Section 5.3. Furthermore, please note, that Sensirio n provides an exemplary sample code on its home page – compare www.sensirion.com/products/catalog/SHT20/. Please note that in case VDD is set to 0 V (GND), e.g. in case of a power off of the SHT2x, the SCL and SDA pads are also pulled to GND. Consequently, the I2C bus is blocked while VDD of the SHT2x is set to 0 V.

5.1 Start Up Sensor

As a first step, the sensor is powered up to the chosen supply voltage VDD (between 2.1 V and 3.6 V). After power-up, the sensor needs at most 15 ms, while SCL is high, for reaching id le state, i.e. to be ready accepting commands from the master (MCU). Current consumption during start up is 350 µA maximum. Whenever the sensor is powered up, but not performing a measu rement or communicating, it is automatically in idle state (sleep mode).

5.2 Start / Stop Sequence

Each transmi ssion sequence begins with Start condition (S) and ends with Stop condition (P) as displayed in Figure 13 and Figure 14. Figure 13 Transmission Start c ondition (S) - a high to low transition on the SDA line while SCL is high. The Start condition is a unique state on the bus created by the master, indicating to the slaves the beginning of a transmission sequence (bus is considered busy after a Start). Figure 14 Transmission Stop c ondition (P) - a low to high transition on the SDA line while SCL is high. The Stop condition is a unique state on the bus created by the master, indicating to the slaves the end of a transmission sequence (bus is considered free after a Stop).

5.3 Sending a Command

After sendi ng the Start condition, the subsequent I 2C header consists of the 7-bit I2C device address ‘1000’000’ and an SDA direction bit (Read R: ‘1’ , Write W: ‘0’). The sensor indicates the proper reception of a byte by pulling the SDA pin low (ACK bit) after the f alling edge of t he 8th SCL clock . After the issue of a measurement command (‘1110’0011’ for temperature, ‘ 1110’0101’ for relative humidity’), the MCU must wait for the measurement to complete. The basic commands are summarized in Table SCL 70% 30% tSCLL 1/fSCL tSCLH tR tF SDA 70% 30% tSU tHD SDA valid read DATA IN tR SDA 70% 30% DATA OUT tVD tF SDA valid write SDA SCL 70% 30% 70% 30% SDA SCL 70% 30% 70% 30%

www.sensirion.com / D1 Version 5 – October 2022 8/14 Command Comment Code Trigger T measurement hold master 1110’0011 Trigger RH measurement hold master 1110’0101 Trigger T measurement no hold master 1111’0011 Trigger RH measurement no hold master 1111’0101 Write user register 1110’0110 Read user register 1110’0111 Soft reset 1111’1110 Table 6 Basic command set, RH stands for relative humidity, and T stands for temperature Hold master or no hold master modes are explained in next Section.

5.4 Hold / No Hold Master Mode

There are two different operation modes to communicate with the se nsor: Hold Master mode or No Hold Master mode. In the first case the SCL line is blocked (controlled by sensor) during measurement process while in the latter case the SCL line remains open for other communication while the sensor is processing the measure ment. No hold master mode allows for processing other I 2C communication tasks on a bus while the sensor is measuring. A communication sequence of the two modes is displayed in Figure 15 and Figure 16, respectively. In the hold master mode , the SHT2x pulls down the SCL line while measuring to force the master into a wait s tate. By releasing the SCL line the sensor indicates that internal processing is terminat ed and that tran smission may be continued. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 S 1 0 0 0 0 0 0 0 ACK 1 1 1 0 0 1 0 1 ACK I2C address + write Command (see Table 6) 19 20 21 22 23 24 25 26 27 S 1 0 0 0 0 0 0 1 ACK Measurement I2C address + read Hold during measurement 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 0 1 1 0 0 0 1 1 ACK 0 1 0 1 0 0 1 0 ACK Data (MSB) Data (LSB) Stat. 46 47 48 49 50 51 52 53 54 0 1 1 0 0 1 0 0 NACK P Checksum Figure 15 Hold master communication sequence – grey blocks are controlled by SHT2x . Bit 45 may be changed to NACK followed by Stop condition (P) to omit checksum transmission. In no hold master mode, the M CU has to poll for the termination of the internal processing of the sensor. This is done by s ending a Start condition followed by the I 2C header (1000’0001) as show n in Figure 16. If the internal processing is finished, the sensor acknowledges the poll of the MCU and data can be read by the MCU. If the measurement processing is not finished the sensor answers no ACK bit and t he Start condition must be issued once more. When using the no hold master mode it is recommended to include a wait period of 18.5 µs after the reception of the sensor’s ACK bit (bit 18 in Figure 16) and before the Stop condition (see section 5.8). For both modes, since the maximum resolution of a measurement is 1 4 bit, the two last least significant bits (LSBs, bits 43 and 44) are used for transmitting status information. Bit 1 of the t wo LSBs indicates the measurement type (‘0’: temperature, ‘1’ humidity). Bit 0 is currently not assigned. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 S 1 0 0 0 0 0 0 0 ACK 1 1 1 1 0 1 0 1 ACK wait P I2C address + write Command (see Table 6) 20µs 19 20 21 22 23 24 25 26 27 Measurement S 1 0 0 0 0 0 0 1 NACK P measuring I2C address + read 19 20 21 22 23 24 25 26 27 Measurement S 1 0 0 0 0 0 0 1 ACK continue measuring I2C address + read 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 0 1 1 0 0 0 1 1 ACK 0 1 0 1 0 0 1 0 ACK Data (MSB) Data (LSB) Stat. 46 47 48 49 50 51 52 53 54 0 1 1 0 0 1 0 0 NACK P Checksum Figure 16 No Hold master communication sequence – grey blocks are controlled by SHT2x . If measurement is not completed upon “read” command, sens or does not provide ACK on bit 27 (more of these iterations are possible). If bit 45 is changed to NACK followed by Stop condition (P) checksum transmission is omitted. In the examples given in Figure 15 and Figure 16 the sensor output is S RH = ‘0110’0011’0101’00 00’. F or the calculation of physical values Status Bits must be set to ‘0’ – see Chapter 6. The maximum duration for measurements depends on the type of measurement and resolution chosen – values are displayed in Table 7. Maximum values shall be chosen for the communication planning of the MCU.

www.sensirion.com / D1 Version 5 – October 2022 9/14 Resolution RH typ RH max T typ T max Units 14 bit 66 85 ms 13 bit 33 43 ms 12 bit 22 29 17 22 ms 11 bit 12 15 9 11 ms 10 bit 7 9 ms 8 bit 3 4 ms Table 7 Measurement time s for RH and T measurements at different resolutions. Typical values are recommende d for calculating energy co nsumption while maximum values shall be applied for calculating waiting times in communication. Please note: I 2C communication allows for repeated Start conditions (S) without closing p rior sequence with Stop condition (P) – compare Figures 1 5, 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 u sed for rebooting the sensor system w ithout switching the power off and on again. Upon reception of this command, the sensor system reinitializes and starts operation according to the default settings – with the exception of the heater bit in the user register (see Sect. 5.4). The soft reset takes less than 15 ms. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 S 1 0 0 0 0 0 0 0 ACK 1 1 1 1 1 1 1 0 ACK P I2C address + write Soft Reset Figure 17 Soft Reset – grey blocks are controlled by SHT2x.

5.6 User Register

The conten t of User Register is described in Table 8. Please note that reserved bits must not be changed and default values of respective reserved bits m ay change over time without prior notice . Therefore, for any writing to the User Register, default values of reserved bits must be read first . Thereafter, the full User Register string is composed of respective default values of reserved bits and the remainder of accessible bits optionally with default or non-default values. The end of battery alert is activated when the battery power falls below 2.25 V. The heater is intended to be used for functionality diagnosis – relative humidity drops upon rising temperature. The heater consumes about 5.5 mW and provides a temperature increase of about 0.5 – 1.5°C. OTP Reload is a safety feature and loads the entire OTP settings to the register, except for the heater bit, before every measurement. This feature is dis abled per default and is not recommended for use. Please use Soft Reset instead – it contains OTP Reload. Bit # Bits Description / Coding Default 7, 0 2 Measurement resolution RH T ‘00’ 12 bit 14 bit ‘01’ 8 bit 12 bit ‘10’ 10 bit 13 bit ‘11’ 11 bit 11 bit ‘00’ 6 1 Status: End of battery13 ‘0’: VDD > 2.25V ‘1’: VDD < 2.25V ‘0’ 3, 4, 5 3 Reserved 2 1 Enable on-chip heater ‘0’ 1 1 Disable OTP Reload ‘1’ Table 8 User Register. Cut -off value for End of Battery signal may vary by ±0. 1V. Reserved bits must not be changed. “OTP reload” = ‘0’ l oads default settings after each time a measurement command is issued. An example for I2C communication reading and writing the User Register is given in Figure 18. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 S 1 0 0 0 0 0 0 0 ACK 1 1 1 0 0 1 1 1 ACK I2C address + write Read Register 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 S 1 0 0 0 0 0 0 1 ACK 0 0 0 0 0 0 1 0 NACK I2C address + read Register content 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 S 1 0 0 0 0 0 0 0 ACK 1 1 1 0 0 1 1 0 ACK I2C address + write Write Register 55 56 57 58 59 60 61 62 63 0 0 0 0 0 0 1 1 ACK P Register content to be written Figure 18 Read and write register sequence – grey blocks are controlled by SHT2x. In this example, the resolution is set to 8bit / 12bit.

5.7 CRC Checksum

SHT21 provides a CRC -8 checksum for error dete ction. The polynomial used is x8 + x5 + x4 +1. For more details and implementation please refer to the application note “CRC Checksum Calculation for SHT2x”.

13 This status bit is updated after each measurement

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5.8 I2C Communication Recommendation

Uncontrolled operation in the No-Hold Master Mode (see section 5.4) can very r arely result in false offse ts of the temperature or relative humid ity measurement values 14. These offsets can occur, if a rising edge on the SCL falls within 15 µs to 18.5 µs after the sensor has sent an ACK bit, w hich confirms the correct r eception of a measurement command. In this time window the sen sor’s calibration data stored in the O TP memory , might be corrupted during transmission to the w orking memory . Once the offsets manifest in the measur ement data, it will remain until the next soft or hard reset. These offsets can be completely avoided using one of t he following four workarounds: 1. Recommended: Avoiding of rising edges in clock line (SCL) during critical time window. To this end the stop condition from the master should be sen t >18.5 µs after the ACK bit is send from the slave. This prevents the offset to occur under all circumstances. Figure 19 Stop condition after critical time window 2. Sending the stop condition before the critical time window, i.e. <15 µs and other communications after 18.5 µs. Figure 20 Stop condition before critical time window 3. Operating in the Hold-Master mode only (see section 5.4). 4. Performing an OTP reload each time a measurement command is is sued. This entails copying the content of the OTP into the working memory , which results in an increased measuremen t time of aro und 2.5 ms. This can be achieved by changing the relevant bit in the user register. As part of the OTP reload, all values in the user register are reinitialized to their default values (except the heater bit). Therefore, the bit (BIT 1) in the user register that controls the OTP must be changed prior to every measurement (see section 5.6).

14 If the sensor is operated using Sensibus commands the offset will not occur

5.9 Serial Number

SHT21 provides an e lectronic identification code. For instructions on how to read the identification code please refer to the A pplication Note “Electronic Identification Code” – to be downloaded from the web page www.sensirion.com/products/catalog/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. in frames of 8 bit length where the most significant bit (MSB) is tr ansferred first (left aligned). Each byte is followed by an acknowledge bit. The two status bits, the last bits of LSB, must be set to ‘0’ before calculating physical values. In the example of Figure 15 and Figure 16, the transferred 16 bit relative humidity data is ‘0110’0011’0101’0000’ = 25424.

6.1 Relative Humidity Conversion

With the relative humidity signal out put SRH the relative humidity RH is obtained by the following formula (result in %RH), no matter which resolution is chosen: RH S1256 RH +−= In the example given in Figure 15 and Figure 16 the relative humidity results to be 42.5 %RH. The physical value RH given above corresponds to the relative humidity above l iquid water according to World Meteorological Organization (WMO). F or relative humidity above ice RHi the values need to be transformed from relative humidity above water RHw at temperature t. The equation is given in the following, compare also Application Note “Introduction to Humidity”: = tλ tβ tλ tβRHRH i i w w wi expexp Units a re %RH for relative humidity and °C for temperature. The corresponding coefficients are defined as follows: βw = 17.62, λw = 243.12°C, βi = 22.46, λi = 272.62°C.

6.2 Temperature Conversion

The temperature T is calculated by inserting temperature signal output ST into the following formula (result in °C), no matter which resolution is chosen: T

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7 Environmental Stability

The SHT2x sensor series were tested based on AEC- Q100 Rev. G qualification test method where applicable. Sensor specifications are tested to prevail under the AEC - Q100 temperature grade 1 test conditions listed in Table 915. Environment Standard Results16 HTOL 125°C, 408 hours Pass TC -50°C - 125°C, 1000 cycles Pass UHST 130°C / 85 %RH / ≈2.3 bar, 96 h Pass THB 85°C / 85 %RH, 1000 h Pass HTSL 150°C, 1000h Pass ELFR 125°C, 48h Pass ESD immunity HBM 4 kV, MM 200 V, CDM 750V/500V (corner/other pins) Pass Latch-up force current of ±100 mA with Tamb = 125°C Pass Table 9: Performed qualification test series . HTOL = High Temperature Operating Lifetime, TC = Temperature Cycles, UHST = Unbiased Highly accelerated Stress Test, THB = Temperature Humidity Biased , HTSL = High Temperatur e Storage Lifetime, ELFR = Early Life Failure Rate. For details on ESD see Sect.4.1. Sensor performance under other test conditions cannot be guaranteed and is not part of the sensor specifications. Especially, no guarantee can be given for sensor performance in the field or for customer’s specific application. If sensors are qualified for reliability and behavior in extreme conditions, please make sure that they experience same conditions as the reference sensor. It should be t aken into account that response times in assemblies may be longer, hence enough dwell time for the measurement shall be granted. For detailed information please consult Application Note “ Testing Guide”.

8 Packaging

8.1 Packaging Type

SHT2x sensors are provided i n D FN packaging ( in analogy wit h QFN packaging). DF N stands for Dual Flat No leads. The sensor chip is mounted to a lead frame m ade of Cu and pla ted with Ni/Pd/ Au. Chip and lead frame are over molded by green epoxy -based mold compound. Please note that side walls of sensors are diced and hence lead 15 Temperature range is -40 to 125°C (AEC-Q100 temperature grade 1). 16 According to accuracy and long term drift specification given on Page 2. frame at diced edge is not covered with respective protective coating. The total weight of the sensor is 25 mg.

8.2 Filter Cap and Sockets

For SHT2x a filter cap SF2 will is available . It is designed for fast respon se times and compact size. Plea se find the datasheet on Sensirion’s web page. For testing of SHT2x sensors sockets , such as from Plastronics, part number 10LQ50S13030 are recommended.

8.3 Traceability Information

All SHT2 x are laser marked with an alphanumeric , five - digit code on the sensor – see Figure 21. The marking on the sensor consists of two lines with five digits each. The first line den otes the sensor type (SHT21). The first digit of the second line defines th e output mode (D = digital, Sensibus and I2C, P = PWM, S = SDM). The second digit defines the manufacturing year (0 = 2010, 1 = 2011, etc.). The last three digits represent an alphanumeric tracking code. That code can be decoded by Sensirion only and allow s for tracking on batch level through production, calibration and testing – and will be provided upon justified request. Figure 21 Laser marking on SHT21. For details see text. Reels are also labeled, as displayed in Figure 22 and Figure 23, and give additional traceability information. Figure 22: First label on reel: XX = Sensor Type (21 for SHT21), O = O utput mode (D = Digital, P = PWM, S = SDM), N N = product revision no. , Y = last digit of year, RRR = number of sensors on reel d ivided by 10 (200 for 2000 units), TTTTT = Traceability Code. SHT21 D0AC4 Lot No.: XXO-NN-YRRRTTTTT Quantity: RRRR RoHS: Compliant Lot No.

www.sensirion.com / D1 Version 5 – October 2022 12/14 Figure 23: Second label on reel: For Device Type and Part Order Number (See Packaging Information on page 2) , Delivery Date (also Date Cod e) is date of packaging of sensors (DD = day, MM = month, YYYY = year), CCCC = Sensirion order number.

8.4 Shipping Package

SHT2x are provided in tape & reel shipment packaging, sealed into antistatic ESD bags. Standard packaging sizes are 400, 1500 and 5000 units per reel. For SHT21, e ach reel contains 440 mm (55 pockets) header tape and 200 mm (25 pockets) trailer tape. The drawing of the packaging tapes with sensor orientation is shown in Figure 24. The reels are provided in sealed antistatic bags. Figure 24 Sketch of packaging tape and sensor orientation. Header tape is to the right and trailer tape to the left on this sketch.

9 Compatibility to SHT1x / 7x protocol

SHT2x sensors may be run by communicating with the Sensirion specific communication protocol used for SHT1x and SHT7x. In case such p rotocol is applied please refer to the communication chapter of datasheet SHT1x or SHT7x. Please note that reserved s tatus bits of user register must not be changed. Please understand that with the SHT1x/7x communication protocol only functions described i n respective datasheets can be used except for the OTP Reload function that is not set to default on SHT2x. As an alternative to OTP Reload the soft reset may be used. 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 RES RH S1256 RH +−= and for temperature T RES T RES is the chosen respective resolution, e.g. 12 (12 bit) for relative humidity and 14 (14 bit) for temperature.

10 Bibliography

[1] Sensirion, "Handling Instructions for Humidity Sensors," 2020. 8.0 2.0 4.0 0.3 1.3 R0.3 MAX R0.25 Ø1.5 MIN Ø1.5 MIN 3.3 0.25 3.3 1.75 5.5 12.0 Device Type: 1-100PPP-NN Description: Humidity & Temperature Sensor SHTxx Part Order No. 1-100PPP-NN or Customer Number Date of Delivery: DD.MM.YYYY Order Code: 46CCCC / 0

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Revision History

Date Version Page(s) Changes 6 May 2009 0.3 1 – 9 Initial preliminary release 21 January 2010 1.0 1 – 4, 7 – 10 Complete revision. For complete revision list please require respective document. 5 May 2010 1.1 1 – 12 Typical specification for temperature sensor. Elimination of errors. For detailed information, please require complete change list at info@sensirion.com.

9 May 2011

2 1 – 7, 10 – Updated temperature accuracy specifications, MSL and standards. Elimination of errors. For detailed information, please require complete change list at info@sensirion.com. December 2011 3 1, 7-10 Tolerance of threshold value for low battery signal, minor text adaptations and corrections. May 2014 4 1-4, 7-8, 9-10 Sensor window dimension updated, several minor adjustments October 2022 5 10 Changed wait from 20 µs to 18.5 µs in Figure 16 and added a corresponding clarification chapter 5.8 I2C communication recommendation, corrected typos, added bibliography, updated important notices.

www.sensirion.com / D1 Version 5 – October 2022 14/14 Important Notices Warning, Personal Injury Do not use this product as safety or emergency stop devices or in any other application where failure of the product could re sult in personal injury. Do not use this product for applications other than its intended and authorized use. Before installing, ha ndling, 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. If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify and hold harmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if SENSIRION shall be allegedly negligent with respect to the design or the manufacture of the product. ESD Precautions The inher ent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESD -induced damage and/or degradation, take customary and statutory ESD precautions when handling this product. See application note “ESD, Latchup and EMC” for more information. Warranty SENSIRION warrants solely to the original purchaser of this product for a period of 12 months (one year) from the date of del ivery that this product shall be of the quality, material and workmanship defined in SENSIRION’s pub lished specifications of the product. Within such period, if proven to be defective, SENSIRION shall repair and/or replace this product, in SENSIRION’s discretion, free of charge to the Buyer, provided that:

• notice in writing describing the defects shall be given to SENSIRION within fourteen (14) days after their appearance;
• such defects shall be found, to SENSIRION’s reasonable satisfaction, to have arisen from SENSIRION’s faulty design, material, or workmanship;
• the defective product shall be returned to SENSIRION’s factory at the Buyer’s expense; and
• the warranty period for any repaired or replaced product shall be limited to the unexpired portion of the original period. This warranty does not apply to any equipment which has not been installed and used within the specifications recommended by SENSIRION for the intended and proper use of the equipment. EXCEPT FOR THE WARRANTIES EXPRESSLY SET FORTH HEREIN, SENSIRION MAKES N O WARRANTIES, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THE PRODUCT. ANY AND ALL WARRANTIES, INCLUDING WITHOUT LIMITATION, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE EXPRESSLY EXCLUDED AND DECLINED. SENSIRION is only liable for defects of this product arising under the conditions of operation provided for in the data sheet and proper use of the goods. SENSIRION explicitly disclaims all warranties, express or implied, for any period during which the goods are operated or stored n ot in accordance with the technical specifications. SENSIRION does not assume any liability arising out of any application or use of any product or circuit and specifically disclaims any and all liability, including without limitation consequential or inci dental damages. All operating parameters, including without limitation recommended parameters, must be validated for each customer’s applications by customer’s technical experts. Recommended parameters can and do vary in different applications. SENSIRION reserves the right, without further notice, (i) to change the product specifications and/or the information in this document a nd (ii) to improve reliability, functions and design of this product. Copyright © 2022, by SENSIRION. CMOSens® is a trademark of Sensirion. All rights reserved Headquarters and Subsidiaries Sensirion AG Laubisruetistr. 50 CH-8712 Staefa ZH Switzerland phone: +41 44 306 40 00 fax: +41 44 306 40 30 info@sensirion.com www.sensirion.com Sensirion Inc., USA phone: +1 312 690 5858 info-us@sensirion.com www.sensirion.com Sensirion Korea Co. Ltd. phone: +82 31 337 7700~3 info-kr@sensirion.com www.sensirion.com/kr Sensirion Japan Co. Ltd. phone: +81 3 3444 4940 info-jp@sensirion.com www.sensirion.com/jp Sensirion China Co. Ltd. phone: +86 755 8252 1501 info-cn@sensirion.com www.sensirion.com/cn Sensirion Taiwan Co. Ltd phone: +886 3 5506701 info@sensirion.com www.sensirion.com To find your local representative, please visit www.sensirion.com/distributors