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Datasheet SHT21
Humidity and Temperature Sensor Fully calibrated Digital output, I2C interface Low power consumption Excellent long term stability DFN type package - reflow solderable
Product Summary SHT21, the new humidity and temperature sensor of Sensirion is about to set new standards in terms of size 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 signals in digital, true I2C format. With a completely new designed CMOSens(R) chip, a reworked capacitive type humidity sensor and an improved band gap temperature sensor the performance has been lifted even beyond the outstanding level of the previous sensor generation (SHT1x and SHT7x). For example, measures have been taken to stabilize the behavior at high humidity levels. Dimensions
3.0 0.3 typ
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 SHT21 can be changed by command (8/12bit up to 12/14bit for RH/T), low battery can be detected and a checksum helps to improve communication reliability. With made improvements and the miniaturization of the sensor the performance-to-price ratio has been improved - and eventually, any device should benefit from the cutting edge energy saving operation mode. For testing SHT21 a new evaluation Kit EK-H4 is available.
Sensor Chip SHT21 features a generation 4C CMOSens(R) 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.
1.1
0.2
SHT21 D0AC4
0.8 typ
2.0 typ 1.4 typ
3.0
2.2
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 SHT21 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.
Bottom View
NC VDD SCL
0.4
0.75
0.3
0.4
1.5
2.4
1.0
1.0
NC
VSS
SDA
Figure 1: Drawing of SHT21 sensor package, dimensions are given in mm (1mm = 0.039inch), tolerances are 0.1mm. Die pad (centre pad) is internally connected to VSS. NC are floating. VSS = GND, SDA = DATA.
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Sensor Performance
Relative Humidity1234
Parameter Resolution 1 Accuracy tolerance 2 Repeatability Hysteresis Nonlinearity Response time 3 63% Operating Range extended 4 Long Term Drift 5 normal
RH (%RH) 10 maximal tolerance 8 6 4
1.0
Temperature567
min typ 0.04 0.7 max Units %RH %RH %RH %RH %RH %RH %RH s 100 < 0.5 %RH %RH/yr Parameter Resolution 1 Accuracy tolerance 2 Repeatability Operating Range extended 4 Response Time 7 Long Term Drift 63% -40 -40 5 < 0.04 Condition 14 bit 12 bit typ max min typ 0.01 0.04 max Units C C C C C C F s C/yr
Condition 12 bit 8 bit typ max
2.0 see Figure 2 0.1 1 <0.1 8 0
0.3 see Figure 3 0.1 125 257 30
T (C) 3.0
typical tolerance
2.5 2.0 1.5
2 0 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity (%RH)
0.5 0.0 -40 -20 0 20 40 60 80 100 120 Temperature (C)
Figure 2 Typical and maximal tolerance at 25C for relative humidity. For extensive information see Users Guide, Sect. 1.2.
Figure 3 Maximal tolerance for temperature sensor in C.
Electrical Specification
Parameter Conditions min typ max Units Supply Voltage, VDD 2.1 3.0 3.6 V sleep mode 0.15 0.4 A Supply Current, IDD 6 measuring 270 300 330 A sleep mode 0.5 1.2 W 6 Power Dissipation measuring 0.8 0.9 1.0 mW average 8bit 1.5 W VDD = 3.0 V 5.5mW, T = + 0.5-1.5C Heater Communication digital 2-wire interface, true I2C protocol Table 1 Electrical specification. For absolute maximum values see Chapter 3 of Users Guide.
1
Packaging Information
Sensor Type SHT21 Packaging Tape & Reel Tape & Reel Tape & Reel Quantity 400 1500 5000 Order Number 1-100707-01 1-100645-01 1-100694-01
This datasheet is subject to change and may be amended without prior notice.
Default measurement resolution is 14bit (temperature) / 12bit (humidity). It can be reduced to 12/8bit, 11/11bit or 13/10bit by command to user register. 2 Accuracies are tested at Outgoing Quality Control at 25C (77F) and 3.0V. Values exclude hysteresis and non-linearity and are applicable to noncondensing environments only. 3 Time for achieving 63% of a step function, valid at 25C 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 200hours at 90%RH). For more details please see Section 1.1 of the Users Guide.
5
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 = 3.0V and T<60C. The average value is based on one 8bit measurement per second. 7 Response time depends on heat conductivity of sensor substrate.
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Datasheet SHT21
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 "Reconditioning Procedure" for eliminating the offset. Prolonged exposure to extreme conditions may accelerate ageing.
Relative Humidity (%)
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 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. 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 mask10 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 120m to 150m larger than the pad size, providing a 60m to 75m 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.
0.4 0.3
0.2
100 80 60 40 20 0 -40 -20 0 20 40 60 80 100 120 Temperature (C)
Normal Range
Max. Range
Figure 4 Operating Conditions
1.2 RH accuracy at various temperatures Maximal tolerance for RH accuracy at 25C is defined in Figure 2. For other temperatures maximal tolerance has been evaluated to be within limits displayed in Figure 58.
100 90 80 70 60 50 40 30 20 10 0
Relative Humidity (%RH)
6
5
1.6
0.7
4
3
3
3
4
6
2.4
6
5
4 5
5
7
1.0
1.0
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 - 80C.
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.
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
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
Details on how Sensirion is specifying and testing accuracy performance are planned to be published on the Sensirion web page.
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.
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0.2
0.4
5 4
5
7
8
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Datasheet SHT21
the package. The die pad aperture should cover about 70 - 90% of the pad area - say up to 1.4mm x 2.3mm centered on the thermal land area. It can also be split in two openings. Due to the low mounted height of the DFN, "no clean" type 3 solder paste11 is recommended as well as Nitrogen purge during reflow.
TP tP
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. 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 10C - 50C 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 PE-HD13. In manufacturing and transport the sensors shall be prevented of high concentration of chemical solvents and long exposure times. Out-gassing of glues, adhesive tapes and stickers or out-gassing packaging material such as bubble foils, foams, etc. shall be avoided. Manufacturing area shall be well ventilated. For more detailed information please consult the document "Handling Instructions" or contact Sensirion. 2.3 Reconditioning Procedure As stated above extreme conditions or exposure to solvent vapors may offset the sensor. The following reconditioning procedure may bring the sensor back to calibration state: Baking: Re-Hydration: 100 - 105C at < 5%RH for 10h 20 - 30C at ~ 75%RH for 12h 14.
Temperature
TL TS (max)
tL
preheating
critical zone
Time
Figure 7 Soldering profile according to JEDEC standard. TP <= 260C and tP < 40sec for Pb-free assembly. TL < 220C and tL < 150sec. Ramp-up/down speeds shall be < 5C/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-020D with peak temperatures at 260C during up to 40sec for Pb-free assembly in IR/Convection reflow ovens (see Figure 7). For manual soldering contact time must be limited to 5 seconds at up to 350C12. IMPORTANT: After soldering, the devices should be stored at >75%RH for at least 12h to allow the sensor element to re-hydrate. Otherwise the sensor may read an offset that slowly disappears if exposed to ambient conditions. Alternatively the re-hydration process may be performed at ambient conditions (>40%RH) during more than 5 days. 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 applications with exposure of the sensor to corrosive gases the soldering pads shall be sealed to prevent loose contacts or short cuts. 2.2 Storage Conditions and Handling Instructions Moisture Sensitivity Level (MSL) is 2; hence storage time is limited to one year.
11
2.4 Temperature Effects Relative humidity reading strongly depends on temperature. Therefore, it is essential to keep humidity sensors at the same temperature as the air of which the relative humidity is to be measured. In case of testing or qualification the reference sensor and test sensor must show equal temperature to allow for comparing humidity readings. If the sensor shares a PCB with electronic components that produce 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 ventilation, reduction of copper layers between the sensor and the rest of the PCB or milling a slit into the PCB around the sensor - see Figure 8. Furthermore, there are self-heating effects in case the measurement frequency is too high. To keep self heating below 0.1C, SHT2x should not be active for more than 10% of the time - e.g. maximum two measurements per second at 12bit accuracy shall be made.
Solder types are related to the solder particle size in the paste: Type 3 covers the size range of 25 - 45 m (powder type 42). 12 260C = 500F, 350C = 662F
13 14
For example, 3M antistatic bag, product "1910" with zipper. 75%RH can conveniently be generated with saturated NaCl solution. 100 - 105C correspond to 212 - 221F, 20 - 30C correspond to 68 - 86F
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Datasheet SHT21
3 Interface Specifications
Pin Name Comment 2 VSS Ground 1 SDA Serial Data, bidirectional 6 SCL Serial Clock, bidirectional 5 VDD Supply Voltage 3,4 NC Not Connected, floating
4 5 6
3 2 1
Figure 8 Top view of example of mounted SHT2x with slits milled into PCB to minimize heat transfer.
Table 2 SHT2x pin assignment, NC remain floating
2.5 Light The SHT2x is not light sensitive. Prolonged direct exposure to sunshine or strong UV radiation may age the sensor. 2.6 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, LCP, POM (Delrin), PTFE (Teflon), PEEK, PP, PB, PPS, PSU, PVDF, PVF. For sealing and gluing (use sparingly): Use high filled epoxy for electronic packaging (e.g. glob top, underfill), and Silicone. Out-gassing of these materials may also contaminate the sensor (see Section 1.3). Therefore try to add the sensor as a last manufacturing step to the assembly, store the assembly well ventilated after manufacturing or bake at >50C for 24h to outgas contaminants before packing. 2.7 Wiring Considerations and Signal Integrity Carrying the SCL and SDA signal parallel and in close proximity (e.g. in wires) for more than 10cm 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. Furthermore, slowing down SCL frequency will possibly improve signal integrity. Power supply pins (VDD, VSS) must be decoupled with a 100nF capacitor - see next Section.
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. Power supply pins Supply Voltage (VDD) and Ground (VSS) must be decoupled with a 100nF capacitor, that shall be placed as close to the sensor as possible - see Figure 9. 3.2 Serial clock (SCL) SCL is used to synchronize the communication between microcontroller (MCU) and the sensor. Since the interface consists of fully static logic there is no minimum SCL frequency. 3.3 Serial SDA (SDA) The SDA pin is used to transfer data in and out of the sensor. For sending a command to the sensor, SDA is valid on the rising edge of SCL and must remain stable while SCL is high. After the falling edge of SCL the SDA value may be changed. For safe communication SDA shall be valid tSU and tHD before the rising and after the falling edge of SCL, respectively - see Figure 10. For reading data from the sensor, SDA is valid tVD after SCL has gone low and remains valid until the next falling edge of SCL.
VDD MCU (master) SCL IN SCL OUT SDA IN SDA OUT GND SDA RP RP SCL SHT2x (slave)
C = 100nF
Figure 9 Typical application circuit, including pull-up resistors RP and decoupling of VDD and VSS by a capacitor.
To avoid signal contention the micro-controller unit (MCU) must only drive SDA and SCL low. External pull-up resistors (e.g. 10k), are required to pull the signal high. For the choice of resistor size please take bus capacity requirements into account (compare Table 5). It should be noted that pull-up resistors may be included in I/O circuits
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Datasheet SHT21
of MCUs. See Table 4 and Table 5 for detailed I/O characteristic of the sensor.
1/fSCK tSCKH tSCKL tR tF 70% 30% tSU
DATA IN
4 Electrical Characteristics
4.1 Absolute Maximum Ratings The electrical characteristics of SHT2x are defined in Table 1. The absolute maximum ratings as given in Table 3 are stress ratings only and give additional information. Functional operation of the device at these conditions is not implied. Exposure to absolute maximum rating conditions for extended periods may affect the sensor reliability (e.g. hot carrier degradation, oxide breakdown).
Parameter VDD to VSS Digital IO Pins (SDA, SCL) to VSS Input Current on any Pin min -0.3 -0.3 -100 max 5 VDD + 0.3 100 Units V V mA
SCL
SDA valid write tHD
SDA
SDA valid read tVD
DATA OUT
70% 30% tF tR 70% 30%
SDA
Figure 10 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. Both valid times (SDA read and SDA write) refer to the left SCL toggle. Parameter SCL frequency, fSCL SCL High Time, tSCLH SCL Low Time, tSCLL SDA Set-Up Time, tSU SDA Hold Time, tHD SDA Valid Time, tVD SCL/SDA Fall Time, tF SCL/SDA Rise Time, tR Capacitive Load on Bus Line, CB min 0 0.6 1.3 100 0 0 0 0 0 typ max Units 0.4 MHz s s ns 900 ns 400 ns 100 ns 300 ns 400 pF
Table 3 Electrical absolute maximum ratings
ESD immunity is qualified according to MIL STD 883E, method 3015 (Human Body Model at 2 kV). Latch-up immunity is provided at a force current of 100mA with Tamb = 80C according to JEDEC78A. For exposure beyond named limits the sensor needs additional protection circuit. 4.2 Input / Output Characteristics The electrical characteristics such as power consumption, low and high level input and output voltages depend on the supply voltage. For proper communication with the sensor it is essential to make sure that signal design is strictly within the limits given in Table 4 & 5 and Figure 10.
Parameter Output Low Voltage, VOL Output High Voltage, VOH Output Sink Current, IOL Input Low Voltage, VIL Input High Voltage, VIH Input Current Conditions
VDD = 3.0 V, -4 mA < IOL < 0mA
Table 5 Timing specifications of digital input/output pads for I2C fast mode. Entities are displayed in Figure 10. VDD = 2.1V to 3.6V, T = -40C to 125C, unless otherwise noted.
5 Communication with Sensor
min 0 70% VDD 0 70% VDD
VDD = 3.6 V, VIN = 0 V to 3.6 V
typ -
max Units 0.4 VDD -4 30% VDD VDD 1 V V mA V V uA
SHT21 communicates with true I2C protocol. For information on I2C beyond the information in the following Sections please refer to the following website: http://www.standardics.nxp.com/support/i2c/. Please note that all sensors are set to the same I2C address, as defined in Section 5.3. 15 Furthermore, please note, that Sensirion provides a sample code on its home page - compare www.sensirion.com/sht21. 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 idle state, i.e. to be ready accepting
15 For sensors with alternative I2C address please contact Sensirion via
-
Table 4 DC characteristics of digital input/output pads. VDD = 2.1 V to 3.6 V, T = -40 C to 125 C, unless otherwise noted.
info@sensirion.com.
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Datasheet SHT21
commands from the master (MCU). Current consumption during start up is 350A maximum. 5.2 Start / Stop Sequence Each transmission sequence begins with Start condition (S) and ends with Stop condition (P) as displayed in Figure 11 and Figure 12. SCL
70% 30%
5.4 Hold / No Hold Master Mode There are two different operation modes to communicate with the sensor: 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 measurement. No hold master mode allows for processing other I2C communication tasks on a bus while the sensor is measuring. A communication sequence of the two modes is displayed in Figure 13 and Figure 14, respectively. 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.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
SDA
70% 30%
ACK
S10000000
11100101
Command (see Table 6)
SCL
70% 30%
I2C address + write
19 20 21 22 23 24 25 26 27
SDA
70% 30%
S10000001
I2C address + read
28 29 30 31 32 33 34
ACK
Measurement
Hold during measurement
Figure 12 Transmission Stop Condition (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).
35 36 37 38 39 40 41 42 43 44
ACK
01100011
Data (MSB)
01010010
Data (LSB) Stat.
46 47 48 49 50 51 52 53 54
5.3 Sending a Command After sending the Start condition, the subsequent I2C 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 falling edge of the 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 6. Hold master or no hold master modes are explained in next Section.
Command Trigger T measurement Trigger RH measurement Trigger T measurement Trigger RH measurement Write user register Read user register Soft reset Comment hold master hold master no hold master no hold master Code 1110'0011 1110'0101 1111'0011 1111'0101 1110'0110 1110'0111 1111'1110
01100011
Checksum
NACK
P
Figure 13 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 MCU has to poll for the termination of the internal processing of the sensor. This is done by sending a Start condition followed by the I2C header (1000'0001) as shown in Figure 14. 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 the Start condition must be issued once more. For both modes, since the maximum resolution of a measurement is 14 bit, the two last LSBs (bits 43 and 44) are used for transmitting status information. Bit 1 of the two LSBs indicates the measurement type (`0': temperature, `1' humidity). Bit 0 is currently not assigned.
Table 6 Basic command set, RH stands for relative humidity, and T stands for temperature
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ACK
ACK
45
Figure 11 Transmission Start Condition (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).
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
S10000000
I2C address + write
11110101
Command (see Table 6)
19 20 21 22 23 24 25 26 27
Measurement
measuring
S10000001
I2C address + read
NACK
5.5 Soft Reset This command (see Table 6) is used for rebooting the sensor system without switching the power off and on again. Upon reception of this command, the sensor system reinitializes and starts operation according to the default settings. 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
ACK
ACK
ACK
19 20 21 22 23 24 25 26 27
S10000000
I2C address + write
11111110
Soft Reset
ACK
P
Measurement
continue measuring
S10000001
I2C address + read
ACK
Figure 15 Soft Reset - grey blocks are controlled by SHT2x.
45
28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
01100011
Data (MSB)
01010010
Data (LSB) Stat.
5.6 User Register The content of user register is described in Table 8. Please note that reserved bits must not be changed.
Bit 7, 0 # Bits 2 Description / Coding Measurement resolution `00' `01' `10' `11' 6 1 RH 12 bit 8 bit 10 bit 11 bit T 14 bit 12 bit 13 bit 11 bit `0' Default `00'
ACK
46 47 48 49 50 51 52 53 54
01100011
Checksum
NACK
P
Figure 14 No Hold master communication sequence - grey blocks are controlled by SHT2x. If measurement is not completed upon "read" command, sensor 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.
ACK
In the examples given in Figure 13 and Figure 14 the sensor output is SRH = `0110'0011'0101'0000'. For 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.
Resolution RH typ RH max 14 bit 13 bit 12 Bit 22 29 11 bit 12 15 10 bit 7 9 8 bit 3 4 T typ 66 33 17 9 T max 85 43 22 11 Units ms ms ms ms ms ms
3, 4, 5 2 1
3 1 1
Status: End of battery16 `0': VDD > 2.25 V `1': VDD < 2.25 V Reserved Enable on-chip heater Disable OTP reload
`0' `1'
Table 8 User Register. Cut-off value for End of Battery signal may vary by 0.05V. Reserved bits must not be changed. "OTP reload" = `0' loads default settings after each time a measurement command is issued.
The End of Battery alert is activated when the battery power falls below 2.25V. The heater is intended to be used for functionality diagnosis - relative humidity drops upon rising temperature. The heater consumes about 5.5mW and provides a temperature increase of about 0.5 - 1.5C. OTP Reload is a safety feature and loads the entire OTP settings to the register before every measurement. This feature is disabled per default and is not recommended for use. Please use Soft Reset instead - it contains OTP Reload. An example for I2C communication reading and writing the User Register is given in Figure 16. It is important that first the content of the register is read in order getting the default values. Hereafter, the resolution is changed by configuring register. Please note that the reserved userregister bits must not be changed.
16
Table 7 Measurement times for RH and T measurements at different resolutions. Typical values are recommended for calculating energy consumption while maximum values shall be applied for calculating waiting times in communication.
Please note: I2C communication allows for repeated Start conditions (S) without closing prior sequence with Stop condition (P) - compare Figures 13, 14 and 16. Still, any sequence with adjacent Start condition may alternatively be closed with a Stop condition.
This status bit is updated after each measurement
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
S10000000
I2C address + write
11100111
Read Register
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
Meteorological Organization (WMO). For 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:
t RH i RH w exp w t w t exp i t i
ACK
S10000001
I2C address + read
00000010
Register content
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
NACK
ACK
ACK
S10000000
I2C address + write
55 56 57 58 59 60 61
11100110
Write Register
62 63
Units are %RH for relative humidity and C for temperature. The corresponding coefficients are defined as follows: w = 17.62, w = 243.12C, i = 22.46, i = 272.62C. 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:
ACK
00000011
Register content to be written
ACK
P
Figure 16 Read and write register sequence - grey blocks are controlled by SHT2x. In this example, the resolution is set to 8bit / 12bit.
ACK
5.7 CRC Checksum For implementing CRC8 checksum please refer to Wikipedia (http://en.wikipedia.org/wiki/crc8). 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.
T 46.85 175.72
ST 216
7 Environmental Stability
The SHT2x sensor series were tested according to AECQ100 Rev. F qualification test method. Sensor specifications are tested to prevail under the AEC-Q100 temperature grade 2 test conditions listed in Table 917. 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.
Environment Standard HTSL 125C, 1000 hours TC UHST THU -50C - 125C, 1000 cycles Acc. JESD22-A104-C 130C / 85%RH, 96h 85C / 85%RH, 1000h Results18 Within specifications Within specifications Within specifications Within specifications Qualified
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 transferred 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 13 and Figure 14, the transferred 16 bit relative humidity data is `0110'0011'0101'0000' = 25424. 6.1 Relative Humidity Conversion With the relative humidity signal output SRH the relative humidity RH is obtained by the following formula (result in %RH), no matter which resolution is chosen:
ESD immunity MIL STD 883E, method 3015 (Human Body Model at 2kV) Latch-up force current of 100mA with Qualified Tamb = 80C, acc. JEDEC 17
S RH 6 125 RH 216
In the example given in Figure 13 and Figure 14 the relative humidity results to be 42.5%RH. The physical value RH given above corresponds to the relative humidity above liquid water according to World
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Table 9: Qualification tests: HTSL = High Temperature Storage Lifetime, TC = Temperature Cycles, UHST = Unbiased Highly accelerated Stress Test, THU = Temperature Humidity Unbiased.
17
Sensor operation temperature range is -40 to 105C according to AEC-Q100 temperature grade 2. 18 According to accuracy and long term drift specification given on Page 2.
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Datasheet SHT21
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 taken 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 "Qualification Guide".
Lot No.: Quantity: RoHS:
Lot No.
XXO-NN-YRRRRTTTT RRRR Compliant
8 Packaging
8.1 Packaging Type
SHT2x sensors are provided in DFN packaging (in analogy with QFN packaging). DFN stands for Dual Flat No leads. The sensor chip is mounted to a lead frame made of Cu and plated 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 frame at diced edge is not covered with respective protective coating. The total weight of the sensor is 25mg. 8.2 Filter Cap and Sockets For SHT2x a filter cap SF2 will be provided. It is designed for fast response times and compact size. Please find the datasheet on Sensirion's web page by February 2010. For testing of SHT2x sensors sockets, such as from Plastronics, part number 10LQ50S13030 are recommended (see e.g. www.locknest.com). 8.3 Traceability Information All SHT2x are laser marked with an alphanumeric, fivedigit code on the sensor - see Figure 17. 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). 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 allows for tracking on batch level through production, calibration and testing - and will be provided upon justified request.
Figure 18: First label on reel: XX = Sensor Type (21 for SHT21), O = Output mode (D = Digital, P = PWM, S = SDM), NN = Chip Version, Y = last digit of year, RRRR = number of sensors on reel, TTTT = Traceability Code.
Device Type: Description:
1-100PPP-NN Humidity & Temperature Sensor SHTxx Part Order No. 1-100PPP-NN or Customer Number Date of Delivery: DD.MM.YYYY Order Code: 45CCCC / 0
Figure 19: Second label on reel: For Device Type and Part Order Number (See Packaging Information on page 2), Delivery Date (also Date Code) 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, each reel contains 440mm (55 pockets) header tape and 200mm (25 pockets) trailer tape. The drawing of the packaging tapes with sensor orientation is shown in Figure 20. The reels are provided in sealed antistatic bags.
8.0 0.3 R0.3 MAX
3.3
2.0 4.0
O0.15 MIN
1.75 5.5
O0.15 MIN
1.3 3.3
SHT21 D0AC4
Figure 17 Laser marking on SHT21. For details see text.
0.25 R0.25
Figure 20 Sketch of packaging tape and sensor orientation. Header tape is to the right and trailer tape to the left on this sketch.
Reels are also labeled, as displayed in Figure 18 and Figure 19, and give additional traceability information.
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Datasheet SHT21
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 protocol is applied please refer to the communication chapter of datasheet SHT1x or SHT7x. Please note that reserved status bits of user register must not be changed. Please understand that with the SHT1x/7x communication protocol only functions described in respective datasheets can be used with the exception of 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 as well as the calculation of physical values in this SHT2x datasheet apply.
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Datasheet SHT21
Revision History
Date 6 May 2009 7 Sept 2009 21 January 2010 Version 0.3 0.5 1.0 Page(s) 1-9 1,3,6,8-9 1 - 4, 7 - 10 Changes Initial preliminary release Revise Section 1.2, Figs. 1, 5 and 9, Table 5. Add Chapter 7 Complete revision. For complete revision list please require respective document from Sensirion.
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 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. 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 inherent 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 delivery that this product shall be of the quality, material and workmanship defined in SENSIRION's published 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 NO 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 not 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 incidental 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 and (ii) to improve reliability, functions and design of this product. Copyright (c) 2010, by SENSIRION. CMOSens(R) is a trademark of Sensirion All rights reserved
Headquarter and Sales Offices
Headquarter SENSIRION AG Laubisruetistr. 50 CH-8712 Staefa ZH Switzerland Sales Office USA: SENSIRION Inc. 2801 Townsgate Rd., Suite 204 Westlake Village, CA 91361 USA Sales Office Japan: SENSIRION JAPAN Co. Ltd. Postal Code: 108-0074 Shinagawa Station Bldg. 7F, 4-23-5, Takanawa, Minato-ku Tokyo, Japan Phone: +41 44 306 40 00 Fax: +41 44 306 40 30 info@sensirion.com http://www.sensirion.com/ Sales Office Korea: SENSIRION KOREA Co. Ltd. #1414, Anyang Construction Tower B/D, 1112-1, Bisan-dong, Anyang-city Gyeonggi-Province South Korea Sales Office China: Sensirion China Co. Ltd. Room 2411, Main Tower Jin Zhong Huan Business Building, Futian District, Shenzhen, Postal Code 518048 PR China Phone: +82 31 440 9925~27 Fax: +82 31 440 9927 info@sensirion.co.kr http://www.sensirion.co.kr
Phone: +1 805 409 4900 Fax: +1 805 435 0467 michael.karst@sensirion.com http://www.sensirion.com/
phone: +86 755 8252 1501 fax: +86 755 8252 1580 info@sensirion.com.cn www.sensirion.com.cn
Phone: +81 3 3444 4940 Fax: +81 3 3444 4939 info@sensirion.co.jp http://www.sensirion.co.jp
Find your local representative at: http://www.sensirion.com/reps
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