1-100769-01 - SENSIRION - Datasheet.Live

www.sensirion.com Version 3 – May 2014 1/14

Datasheet SHT25

Humidity and Temperature Sensor IC

 Fully calibrated with 1.8%RH accuracy

 Digital output, I2C interface

 Low power consumption

 Excellent long term stability

 DFN type package – reflow solderable

Dimensions

Figure 1: Drawing of SHT25 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

SHT25 features a generation 4C CMOSens® chip.

Besides the capacitive relative humidity sensor and the

band gap temperature sensor, the chip contains an

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

processing unit.

Material Contents

While the sensor itself is made of Silicon the sensors’

housing consists of a plated Cu lead-frame and green

epoxy-based mold compound. The device is fully RoHS

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

Additional Information and Evaluation Kits

Additional information such as Application Notes is

available from the web page www.sensirion.com/sht25.

For more information please contact Sensirion via

info@sensirion.com.

For SHT25 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

SHT21

D0AC4

3.0

2.2

1.4 max

3.0

0.3 typ

2.4 max

Product Summary

The SHT25 high accuracy humidity and temperature

sensor of Sensirion has become an industry standard in

terms of form factor and intelligence: Embedded in a

reflow solderable Dual Flat No leads (DFN) package of 3

x 3mm foot print and 1.1mm height it provides calibrated,

linearized sensor signals in digital, I2C format.

The SHT2x sensors contain a capacitive type humidity

sensor, a band gap temperature sensor and specialized

analog and digital integrated circuit – all on a single

CMOSens® chip. This yields in an unmatched sensor

performance in terms of accuracy and stability as well as

minimal power consumption.

Every sensor is individually calibrated and tested. Lot

identification is printed on the sensor and an electronic

identification code is stored on the chip – which can be

read out by command. Furthermore, the resolution of

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

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

communication reliability.

With this set of features and the proven reliability and

long-term stability, the SHT2x sensors offer an

outstanding performance-to-price ratio. For testing SHT2x

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

www.sensirion.com Version 3 – May 2014 2/14

Sensor Performance

Relative Humidity

Parameter

Condition

Value

Units

Resolution1

12 bit

0.04

%RH

8 bit

0.7

%RH

Accuracy tolerance2

typ

1.8

%RH

max

see Figure 2

%RH

Repeatability

0.1

%RH

Hysteresis

1

%RH

Nonlinearity

<0.1

%RH

Response time3

 63%

8

s

Operating Range

extended4

0 to 100

%RH

Long Term Drift5

Typ.

< 0.25

%RH/yr

± 0

± 2

± 4

± 6

± 8

± 10

010 20 30 40 50 60 70 80 90 100

Relative Humidity (%RH)

DRH (%RH)

maximum accuracy

typical accuracy

Figure 2 Typical and maximal tolerance at 25°C for relative

humidity. For extensive information see Users Guide, Sect. 1.2.

Packaging Information

Sensor Type

Packaging

Quantity

Order Number

SHT25

Tape & Reel

400

1-100769-01

Tape & Reel

1500

1-100768-01

1

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 25°C and 3.0V. Values

exclude hysteresis and long term drift and are applicable to non-condensing

environments only.

3

Time for achieving 63% of a step function, valid at 25°C and 1m/s airflow.

4

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

reversible offset with slow kinetics (+3%RH after 60h at humidity >80%RH). For

more details please see Section 1.1 of the Users Guide.

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.

Temperature

Parameter

Condition

Value

Units

Resolution1

14 bit

0.01

°C

12 bit

0.04

°C

Accuracy tolerance2

typ

0.2

°C

max

see Figure 3

Repeatability

0.1

°C

Operating Range

extended4

-40 to 125

°C

Response Time6

 63%

5 to 30

s

Long Term Drift7

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 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

Supply Current, IDD8

sleep mode

-

0.15

0.4

µA

measuring

200

300

330

µA

Power Dissipation8

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.

This datasheet is subject to change and may be amended

without prior notice.

6

Response time depends on heat conductivity of sensor substrate.

7

Max. value is < 0.04°C/y.

8

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 8bit

measurement per second.

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 3/14

Users Guide SHT25

1 Extended Specification

For details on how Sensirion is specifying and testing

accuracy performance please consult Application Note

“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 >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. 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 defined in Figure 2. For

other temperatures, typical accuracy has been evaluated

to be as displayed in Figure 5.

100 ±3 ±2.5 ±2.5 ±2.5 ±2.5 ±2.5 ±3 ±3.5 ±3.5

90 ±3 ±2.5 ±2 ±2 ±2 ±2 ±2.5 ±3 ±3.5

80 ±2.5 ±2 ±1.8 ±1.8 ±1.8 ±2 ±2 ±2.5 ±3

70 ±2.5 ±2 ±1.8 ±1.8 ±1.8 ±1.8 ±2 ±2 ±2.5

60 ±2 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±2 ±2

50 ±2 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±2

40 ±2 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8

30 ±2 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8

20 ±2 ±2 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8 ±1.8

10 ±2.5 ±2.5 ±2 ±2 ±2 ±2 ±2 ±2 ±2

0±3 ±3 ±2.5 ±2.5 ±2.5 ±2.5 ±2.5 ±2.5 ±2.5

010 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 estimations 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

1

2

3

4

5

6

7

8

020 40 60 80 100 120

Temperature (°C)

Supply Current IDD (μA)

Figure 6 Dependency of supply current (sleep mode) versus

temperature at VDD = 3.0V. Please note the variance of the

displayed data may exceed ±25%.

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 7 Typical dependency of supply current (sleep mode)

versus supply voltage at 25°C. Please note the variance of the

displayed data may exceed ±25%.

0

20

40

60

80

100

-40 -20 0 20 40 60 80 100 120

Temperature (°C)

Relative Humidity (%)

Max.

Range

Normal

Range

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 4/14

2 Application Information

2.1 Soldering Instructions

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

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

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

mechanical and electrical connection. Both the I/O pads

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

prevent oxidation and optimize soldering, the bottom side

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

On the PCB the I/O lands

9

should be 0.2mm longer than

the package I/O pads. Inward corners may be rounded to

match the I/O pad shape. The I/O land width should match

the DFN-package I/O-pads width 1:1 and the land for the

die pad should match 1:1 with the DFN package – see

Figure 8.

The solder mask

10

design for the land pattern preferably is

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

mask openings larger than metal pads. For NSMD pads,

the solder mask opening should be about 120μm to

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

design clearance between the copper pad and solder

mask. Rounded portions of package pads should have a

matching rounded solder mask-opening shape to minimize

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

each pad on the PCB should have its own solder mask

opening with a web of solder mask between adjacent

pads.

Figure 8 Recommended metal land pattern for SHT2x. Values

in mm. Die pad (centre pad) and 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

the package. The die pad aperture should cover about 70

– 90% of the pad area – say up to 1.4mm x 2.3mm

9

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

the DFN pads are soldered to.

10

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

covering the connecting lines.

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 paste

11

is recommended as well as Nitrogen

purge during reflow.

Figure 9 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 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 30sec 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

12

.

Immediately after the exposure to high temperatures the

sensor may temporarily 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 immediately 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 applications with exposure of the sensor

to corrosive gases or condensed water (i.e. environments

with high relative humidity) the soldering pads shall 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).

12

260°C = 500°F, 350°C = 662°F

Temperature

Time

tP

TP

TL

TS (max)

tL

preheating

critical zone

1.0

0.3

0.4

1.5

0.4

0.75

0.2

2.4

≤2.3

≤1.4

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 5/14

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.

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

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-HD

13

.

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 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 10.

Furthermore, there are self-heating effects in case 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 12bit accuracy shall be made.

13

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, 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 2.2). Therefore try to

add the sensor as a last manufacturing step to the

assembly, store the assembly well ventilated after

manufacturing or bake at >50°C for 24h 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 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.

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 6/14

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 SHT2x pin assignment, NC must remain floating (top

view)

3.1 Power Pins (VDD, VSS)

The supply voltage of SHT2x must be in the range of 2.1 –

3.6V, recommended supply voltage is 3.0V. 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 11.

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 12. 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 11 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 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

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 12.

Parameter

Conditions

min

typ

max

Units

Output Low

Voltage, VOL

VDD = 3.0 V,

-4 mA < IOL < 0mA

0

-

0.4

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.

SDA

SCL

GND

VDD

MCU (master)

RP

SCL OUT

SDA OUT

SDA IN

SCL IN

C = 100nF

SHT2x

(slave)

1

6

5

2

4

3

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 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 mode. Entities are displayed in Figure 12. 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

SHT25 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.

Furthermore, please note, that Sensirion provides an

exemplary sample code on its home page – compare

www.sensirion.com/sht25.

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 2.1V 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 idle state (sleep

mode).

5.2 Start / Stop Sequence

Each transmission sequence begins with Start condition

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

13 and Figure 14.

Figure 13 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 14 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 ‘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.

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%

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 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

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 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 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

ACK

1

0

1

0

1

ACK

I2C address + write

Command (see Table 6)

19

20

21

22

23

24

25

26

27

S

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

1

0

ACK

Data (MSB)

Data (LSB)

Stat.

46

47

48

49

50

51

52

53

54

0

1

0

1

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 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 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 the Start condition must be

issued once more.

When using the no hold master mode it is recommended

to include a wait period of 20 µs after the reception of the

sensor’s ACK bit (bit 18 in Figure 16) and before the Stop

condition.

For both modes, since the maximum resolution of a

measurement is 14 bit, the two last 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, ‘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

ACK

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

1

NACK

P

measuring

I2C address + read

19

20

21

22

23

24

25

26

27

Measurement

S

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

1

0

ACK

Data (MSB)

Data (LSB)

Stat.

46

47

48

49

50

51

52

53

54

0

1

0

1

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, 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.

In the examples given in Figure 15 and Figure 16 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.

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 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 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 15, 16 and 18. Still, any

sequence with adjacent Start condition may alternatively

be closed with a Stop condition.

5.5 Soft Reset

This command (see Table 6) is used for rebooting the

sensor system without switching the power off and on

again. 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

ACK

1

0

ACK

P

I2C address + write

Soft Reset

Figure 17 Soft Reset – grey blocks are controlled by SHT2x.

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.

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 – 1.5°C.

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.

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

‘00’

6

1

Status: End of battery14

‘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. 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.

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

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

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

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 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 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”.

14

This status bit is updated after each measurement

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 10/14

5.8 Serial Number

SHT25 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/sht25.

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 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 output SRH the relative

humidity RH is obtained by the following formula (result in

%RH), no matter which resolution is chosen:

16

RH

2

S

1256 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 liquid water according to World

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:

































 tλ

tβ

tλ

tβ

RHRH

i

w

wi ex pex p

Units are %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:

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 1 test conditions listed in Table

9

15

.

Environment

Standard

Results16

HTOL

125°C, 408 hours

Pass

TC

-50°C - 125°C, 1000 cycles

Pass

UHST

130°C / 85%RH / ≈2.3bar, 96h

Pass

THB

85°C / 85%RH, 1000h

Pass

HTSL

150°C, 1000h

Pass

ELFR

125°C, 48h

Pass

ESD immunity

HBM 4kV, MM 200V, CDM

750V/500V (corner/other pins)

Pass

Latch-up

force current of ±100mA 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 Temperature

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 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

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

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.

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 11/14

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 is available. It is designed for

fast response times and compact size. Please find the

datasheet on Sensirion’s web page.

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, five-

digit code on the sensor – see Figure 19.

The marking on the sensor consists of two lines with five

digits each. The first line denotes the sensor type

(SHT25). 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 19 Laser marking on SHT25. For details see text.

Reels are also labeled, as displayed in Figure 20 and

Figure 21, and give additional traceability information.

Figure 20: First label on reel: XX = Sensor Type (25 for SHT25),

O = Output mode (D = Digital), 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 21: 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 and 1500 units per reel. For SHT25, 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 22. The reels are provided in

sealed antistatic bags.

Figure 22 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 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

8.0

2.0

4.0

0.3

1.3

R0.3 MAX

R0.25

Ø1.5 MIN

3.3

0.25

3.3

1.75

5.5

12.0

SHT25

D0AC4

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

Lot No.: XXO-NN-YRRRTTTTT

Quantity: RRRR

RoHS: Compliant

Lot No.

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 12/14

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

2

S

1256 RH 

and for temperature T

RES

T

2

S

175.7246.85 T 

RES is the chosen respective resolution, e.g. 12 (12bit) for

relative humidity and 14 (14bit) for temperature.

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 13/14

Revision History

Date

Version

Page(s)

Changes

11 June 2010

0.3

1 – 9

Initial preliminary release

25 October 2010

0.91

1 – 12

Public release

December 2011

2

all

MSL and standards, minor text adaptations and corrections.

May 2014

3

1-4, 7-8, 9-10

Sensor window dimension updated, several minor adjustments

Datasheet SHT25

www.sensirion.com Version 3 – May 2014 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 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

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phone: +41 44 306 40 00

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info@sensirion.com

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phone: +1 805 409 4900

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info@sensirion.co.jp

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phone: +82 31 337 7700~3

info@sensirion.co.kr

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phone: +86 755 8252 1501

info@sensirion.com.cn

www.sensirion.com.cn

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phone: +41 44 927 11 66

info@sensirion.com

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