1-100811-01 - SENSIRION - Datasheet.Live

www.sensirion.com Version 2 – December 2011 1/12

Datasheet STS21

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 STS21 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

STS21 features a generation 4C CMOSens® chip.

Besides 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. For more

information please contact Sensirion via

info@sensirion.com.

For STS21 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

NC

VSS

VDD

Bottom View

STS21

D0AC4

3.0

2.2

0.8 typ

1.4 typ

3.0

0.3 typ

2.0 typ

Product Summary

STS21, the new 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, I2C

format.

Using the same CMOSens® technology as Sensirion‟s

successful and industry proven SHT2x humidity and

temperature sensors, the STS21 offers superior

performance and reliability. The ±0.2°C temperature

specification allows for implementation of the STS21 in

applications with high demands on temperature accuracy.

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

STS21 can be changed by command (11bit up to 14bit),

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.

www.sensirion.com Version 2 – December 2011 2/12

Sensor Performance

Temperature Specification

Parameter

Condition

min

typ

max

Units

Resolution1

14 bit

0.01

°C

12 bit

0.04

°C

Accuracy

tolerance2

typ

0.2

°C

max

see Figure 2

°C

Repeatability

0.1

°C

Operating Range

extended

-40

125

°C

Response Time3

63%

5

30

s

Long Term Drift

< 0.04

°C/yr

± 0.0

± 0.5

± 1.0

± 1.5

± 2.0

-40 -20 0 20 40 60 80 100 120

Temperature (°C)

T (°C)

maximal tolerance

typical tolerance

Figure 2 Typical and maximal tolerance for temperature sensor

in °C

1 Default measurement resolution is 14bit. It can be reduced to 13bit, 12bit or

11bit by command to user register.

2 Accuracies are tested at Outgoing Quality Control at 25°C and 3.0V. Values

exclude long term drift.

3 Response time depends on heat conductivity of sensor substrate.

Electrical Specification

Parameter

Conditions

min

typ

max

Units

Supply Voltage, VDD

2.1

3.0

3.6

V

Supply Current, IDD4

sleep mode

0.15

0.4

µA

measuring

200

300

330

µA

Power Dissipation4

sleep mode

0.5

1.2

µW

measuring

0.6

0.9

1.0

mW

average 11bit

8.6

µW

Communication

digital 2-wire interface, I2C protocol

Table 1 Electrical specification. For absolute maximum

values see Section 4.1 of Users Guide.

Packaging Information

Sensor Type

Packaging

Quantity

Order Number

STS21

Tape & Reel

400

1-100811-01

Tape & Reel

1500

1-100812-01

Tape & Reel

5000

1-100832-01

This datasheet is subject to change and may be amended

without prior notice.

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

fixed VDD = 3.0V and T<60°C. The average value is based on one 11bit

measurement per second.

www.sensirion.com Version 2 – December 2011 3/12

Users Guide STS21

1 Extended Specification

1.1 Electrical Specification

Current consumption as given in Table 1 is dependent on

temperature and supply voltage VDD. For estimations on

energy consumption of the sensor Figures 3 and 4 may be

consulted. Please note that values given in these Figures

are of typical nature and the variance is considerable.

0

1

2

3

4

5

6

7

8

020 40 60 80 100 120

Temperature (°C)

Supply Current IDD (μA)

Figure 3 Typical dependency of supply current (sleep mode)

versus temperature at VDD = 3.0V. Please note that the

variance of these data can be above ±25% of displayed value.

6

8

10

12

14

16

18

20

2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5

Supply Voltage (VDD)

Supply Current IDD (nA)

Figure 4 Typical dependency of supply current (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).

2 Application Information

2.1 Soldering Instructions

The DFN’s die pad (centre pad) and perimeter I/O pads

are fabricated from a planar copper lead-frame by over-

molding leaving the die pad and I/O pads exposed for

mechanical and electrical connection. Both the I/O pads

and die pad should be soldered to the PCB. In order to

prevent oxidation and optimize soldering, the bottom side

of the sensor pads is plated with Ni/Pd/Au.

On the PCB the I/O lands5 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 5.

The solder mask6 design for the land pattern preferably is

of type Non-Solder Mask Defined (NSMD) with solder

mask openings larger than metal pads. For NSMD pads,

the solder mask opening should be about 120μm to

150μm larger than the pad size, providing a 60μm to 75μm

design clearance between the copper pad and solder

mask. Rounded portions of package pads should have a

matching rounded solder mask-opening shape to minimize

the risk of solder bridging. For the actual pad dimensions,

each pad on the PCB should have its own solder mask

opening with a web of solder mask between adjacent

pads.

Figure 5 Recommended metal land pattern for STS21. 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 0.125mm

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

5 The land pattern is understood to be the metal layer on the PCB, onto which

the DFN pads are soldered to.

6 The solder mask is understood to be the insulating layer on top of the PCB

covering the connecting lines.

1.0

0.3

0.4

1.5

0.4

0.7

0.2

2.4

Datasheet STS21

www.sensirion.com Version 2 – December 2011 4/12

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 paste7 is recommended as well as Nitrogen

purge during reflow.

Figure 6 Soldering profile according to JEDEC standard. TP <=

260°C and tP < 30sec for Pb-free assembly. TL < 220°C and tL <

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 STS21, 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 30sec for Pb-free

assembly in IR/Convection reflow ovens (see Figure 6).

For manual soldering contact time must be limited to 5

seconds at up to 350°C.

2.2 Storage Conditions and Handling Instructions

Moisture Sensitivity Level (MSL) is 1, according 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.

During storage, temperature shall be in the range of 10°C

– 50°C.

2.3 Temperature Effects

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 7.

7 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).

Furthermore, there are self-heating effects in case the

measurement frequency is too high. To keep self heating

below 0.1°C, STS21 should not be active for more than

10% of the time – e.g. maximum two measurements per

second at 14bit accuracy shall be made.

Figure 7 Top view of example of mounted STS21 with slits

milled into PCB to minimize heat transfer.

2.4 Light

The STS21 is not light sensitive. Prolonged direct

exposure to sunshine or strong UV radiation may age the

sensor.

2.5 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 Interface Specifications

Name

Comment

1

SDA

Serial Data, bidirectional

2

VSS

Ground

5

VDD

Supply Voltage

6

SCL

Serial Clock, bidirectional

3,4

NC

Not Connected

Table 2 STS21 pin assignment, NC remain floating (top view)

3.1 Power Pins (VDD, VSS)

The supply voltage of STS21 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 8.

3.2 Serial clock (SCL)

SCL is used to synchronize the communication between

microcontroller (MCU) and the sensor. Since the interface

Temperature

Time

tP

TP

TL

TS (max)

tL

preheating

critical zone

1

6

5

2

4

3

Datasheet STS21

www.sensirion.com Version 2 – December 2011 5/12

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 9. 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.

Figure 8 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. 10kΩ), 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

of MCUs. See Table 4 and Table 5 for detailed I/O

characteristic of the sensor.

4 Electrical Characteristics

4.1 Absolute Maximum Ratings

The electrical characteristics of STS21 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

min

max

Units

VDD to VSS

-0.3

5

V

Digital I/O Pins (SDA, SCL)

to VSS

-0.3

VDD + 0.3

V

Input Current on any Pin

-100

100

mA

Table 3 Electrical absolute maximum ratings

ESD immunity is qualified according to JEDEC JESD22-

A114 method (Human Body Model at 4kV), JEDEC

JESD22-A115 method (Machine Model 200V) and ESDA

ESD-STM5.3.1-1999 and AEC-Q100-011 (Charged

Device Model, 750V corner pins, 500V other pins). Latch-

up immunity is provided at a force current of 100mA with

Tamb = 125°C according to JEDEC JESD78. 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 9.

Parameter

Conditions

min

typ

max

Units

Output Low

Voltage, VOL

VDD = 3.0 V,

-4 mA < IOL < 0mA

0

-

0.4

V

Output High

Voltage, VOH

70%

VDD

-

VDD

V

Output Sink

Current, IOL

-

-4

mA

Input Low

Voltage, VIL

0

-

30%

VDD

V

Input High

Voltage, VIH

70%

VDD

-

VDD

V

Input Current

VDD = 3.6 V,

VIN = 0 V to 3.6 V

-

±1

uA

Table 4 DC characteristics of digital input/output pads. VDD =

2.1V to 3.6V, T = -40°C to 125°C, unless otherwise noted.

Figure 9 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.

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

GND

VDD

MCU (master)

RP

SCL OUT

SDA OUT

SDA IN

SCL IN

C = 100nF

STS21

(slave)

Datasheet STS21

www.sensirion.com Version 2 – December 2011 6/12

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 mode. Entities are displayed in Figure 9. VDD = 2.1V to

3.6V, T = -40°C to 125°C, unless otherwise noted. For further

information regarding timing, please refer to

http://www.standardics.nxp.com/support/i2c/.

5 Communication with Sensor

STS21 communicates with 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. 8

Furthermore, please note, that Sensirion provides an

exemplary sample code for SHT21 sensors on its home

page – compare www.sensirion.com/SHT21. This sample

code can be used for STS21 sensors with minor

adjustments (I2C address, no RH measurement).

5.1 Start Up Sensor

As a first step, the sensor is powered up to the chosen

supply voltage VDD (between 2.1V and 3.6V). After

power-up, the sensor needs at most 15ms, while SCL is

high, for reaching idle state, i.e. to be ready accepting

commands from the master (MCU). Current consumption

during start up is 350µA maximum. Whenever the sensor

is powered up, but not performing a measurement or

communicating, it is automatically in sleep mode (idle

state).

5.2 Start / Stop Sequence

Each transmission sequence begins with Start condition

(S) and ends with Stop condition (P) as displayed in Figure

10 and Figure 11.

8 For sensors with alternative I2C address please contact Sensirion via

info@sensirion.com.

Figure 10 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).

Figure 11 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).

5.3 Sending a Command

After sending the Start condition, the subsequent I2C

header consists of the 7-bit I2C device address „1001‟010‟

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,

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 the next

Section.

Command

Comment

Code

Trigger T measurement

hold master

1110‟0011

Trigger T measurement

no hold master

1111‟0011

Write user register

1110‟0110

Read user register

1110‟0111

Soft reset

1111‟1110

Table 6 Basic command set, T stands for temperature

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 12 and Figure 13, respectively.

SDA

SCL

70%

30%

70%

30%

SDA

SCL

70%

30%

70%

30%

Datasheet STS21

www.sensirion.com Version 2 – December 2011 7/12

In the hold master mode, the STS21 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

S

1

0

1

0

1

0

ACK

1

0

1

ACK

I2C address + write

Command (see Table 6)

19

20

21

22

23

24

25

26

27

S

1

0

1

0

1

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

0

1

ACK

0

1

0

1

0

ACK

Data (MSB)

Data (LSB)

Stat.

46

47

48

49

50

51

52

53

54

0

1

0

NACK

P

Checksum

Figure 12 Hold master communication sequence – grey blocks

are controlled by STS21. 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 (1001‟0101) as shown in Figure 13. 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 plus header

byte must be issued once more.

For both modes, since the maximum resolution of a

measurement is 14 bit, the two least significant bits (LSBs,

bits 43 and 44) are used for transmitting status

information. Bit 1 of the two LSBs indicates the

measurement type („0‟: temperature). Bit 0 is currently not

assigned.

In the examples given in Figure 12 and Figure 13 the

sensor output is ST = „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.

Please note: I2C communication allows for repeated Start

conditions (S) without closing prior sequence with Stop

condition (P) – compare Figure 12, Figure 13 and Figure

18. Still, any sequence with adjacent Start condition may

alternatively be closed with a Stop condition.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

S

1

0

1

0

1

0

ACK

1

0

1

ACK

I2C address + write

Command (see Table 6)

19

20

21

22

23

24

25

26

27

Measurement

S

1

0

1

0

1

0

1

NACK

measuring

I2C address + read

19

20

21

22

23

24

25

26

27

Measurement

S

1

0

1

0

1

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

0

1

ACK

0

1

0

1

0

ACK

Data (MSB)

Data (LSB)

Stat.

46

47

48

49

50

51

52

53

54

0

1

0

NACK

P

Checksum

Figure 13 No Hold master communication sequence – grey

blocks are controlled by STS21. 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.

Resolution

T typ

T max

Units

14 bit

66

85

ms

13 bit

33

43

ms

12 Bit

17

22

ms

11 bit

9

11

ms

Table 7 Measurement times for 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.

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 – with the exception of the heater bit in the

user register (see Sect. 5.6). The soft reset takes less than

15ms.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

S

1

0

1

0

1

0

ACK

1

0

ACK

P

I2C address + write

Soft Reset

Figure 14 Soft Reset – grey blocks are controlled by STS21.

Datasheet STS21

www.sensirion.com Version 2 – December 2011 8/12

5.6 User Register

The content of User Register is described in Table 8.

Please note that reserved bits must not be changed and

default values of respective reserved bits may 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.

Bit

# Bits

Description / Coding

Default

7, 0

2

Measurement resolution

„00‟

14 bit

„01‟

12 bit

„10‟

13 bit

„11‟

11 bit

„00‟

6

1

Status: End of battery9

„0‟: VDD > 2.25V

„1‟: VDD < 2.25V

„0‟

3, 4, 5

3

Reserved

2

1

Enable on-chip heater

„0‟

1

Disable OTP Reload

„1‟

Table 8 User Register. Threshold value for End of Battery

signal may vary by ±0.1V. 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.

OTP Reload is a safety feature and loads the entire OTP

settings to the register, with the exception of the heater bit,

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 15.

5.7 CRC Checksum

STS21 provides a CRC-8 checksum for error detection.

The polynomial used is x8 + x5 + x4 +1. For more details

and implementation please refer to the application note

“CRC Checksum Calculation for SHT2x”.

5.8 Serial Number

STS21 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.

9 This status bit is updated after each measurement

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

S

1

0

1

0

1

0

ACK

1

0

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

1

0

1

0

1

ACK

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

1

0

1

0

ACK

1

0

1

0

ACK

I2C address + write

Write Register

55

56

57

58

59

60

61

62

63

0

1

ACK

P

Register content to be written

Figure 15 Read and write register sequence – grey blocks are

controlled by STS21. In this example, the resolution is set to

12bit.

6 Conversion of Signal Output

Default resolution is set to 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 12 and Figure

13, the transferred 16 bit temperature data is

„0110‟0011‟0101‟0000‟ = 25424.

6.1 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:

16

T

2

S

175.7246.85 T

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 2 test conditions listed in Table

910.

10 Temperature range is -40 to 105°C (AEC-Q100 temperature grade 2).

Datasheet STS21

www.sensirion.com Version 2 – December 2011 9/12

Environment

Standard

Results11

HTOL

125°C, 408 hours

Within

specifications

TC

-50°C - 125°C, 1000 cycles

Within

specifications

UHST

130°C / 85%RH / ≈2.3bar, 96h

Within

specifications

THB

85°C / 85%RH, 1000h

Within

specifications

ESD immunity

HBM 4kV, MM 200V, CDM

750V/500V (corner/other pins)

Qualified

Latch-up

force current of ±100mA with

Tamb = 125°C

Qualified

Table 9 Performed qualification test series. HTOL = High

Temperature Operating Lifetime, TC = Temperature Cycles,

UHST = Unbiased Highly accelerated Stress Test, THB =

Temperature Humidity Biased. 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 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 “Testing

Guide”.

8 Packaging

8.1 Packaging Type

STS21 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 Sockets

For testing of STS21 sensors sockets, such as from

Plastronics, part number 10LQ50S13030 are

recommended (see e.g. www.locknest.com).

11 According to accuracy and long term drift specification given on Page 2.

8.3 Traceability Information

All STS21 are laser marked with an alphanumeric, five-

digit code on the sensor – see Figure 16.

The marking on the sensor consists of two lines with five

digits each. The first line denotes the sensor type (STS21).

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 16 Laser marking on STS21. For details see text.

Reels are also labeled, as displayed in Figure 17 and

Figure 18, and give additional traceability information.

Figure 17 First label on reel: O = Output mode (D = Digital), XX

= Sensor Type (21 for STS21), NN = product revision no., Y =

last digit of year, RRR = number of sensors on reel divided by

10 (200 for 2000 units), TTTTT = Traceability Code.

Figure 18 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.

STS21

D0AC4

Device Type: 1-100PPP-NN

Description: Temperature Sensor STSxx

Part Order No. 1-100PPP-NN or Customer Number

Date of Delivery: DD.MM.YYYY

Order Code: 46CCCC / 0

Lot No.: OXX-NN-YRRRTTTTT

Quantity: RRRR

RoHS: Compliant

Lot No.

Datasheet STS21

www.sensirion.com Version 2 – December 2011 10/12

8.4 Shipping Package

STS21 are provided in tape & reel shipment packaging,

sealed into antistatic ESD bags. Standard packaging sizes

are 400, 1500 and 5000 units per reel. For STS21, 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 19. The reels are provided in

sealed antistatic bags.

Figure 19 Sketch of packaging tape and sensor orientation.

Header tape is to the right and trailer tape to the left on this

sketch.

8.0

2.0

4.0

0.3

1.3

R0.3 MAX

R0.25

Ø0.15 MIN

3.3

0.25

3.3

1.75

5.5

12.0

Datasheet STS21

www.sensirion.com Version 2 – December 2011 11/12

Revision History

Date

Version

Page(s)

Changes

April 2011

0.3

all

New preliminary release (based on SHT21 data sheet)

10 June 2011

0.4

2

Quantity of 5000 pcs. added to packaging information

15 July 2011

1

-

Initial Release

December 2011

2

1, 2, 4, 6-8

Average power dissipation value, tolerance of threshold value for low battery signal,

minor text adaptations and corrections.

Datasheet STS21

www.sensirion.com Version 2 – December 2011 12/12

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.

CMOSens® is a trademark of Sensirion

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: +1 805 409 4900

info_us@sensirion.com

www.sensirion.com

Sensirion Japan Co. Ltd.

phone: +81 3 3444 4940

info@sensirion.co.jp

www.sensirion.co.jp

Sensirion Korea Co. Ltd.

phone: +82 31 345 0031 3

info@sensirion.co.kr

www.sensirion.co.kr

Sensirion China Co. Ltd.

phone: +86 755 8252 1501

info@sensirion.com.cn

www.sensirion.com.cn

Sensirion AG (Germany)

phone: +41 44 927 11 66

info@sensirion.com

www.sensirion.com

To find your local representative, please visit www.sensirion.com/contact