www.sensirion.com Version 4 – May 2014 1/14
Datasheet SHT20
Humidity and Temperature Sensor IC
Fully calibrated
Digital output, I2C interface
Low power consumption
Excellent long term stability
DFN type package – reflow solderable
Dimensions
Figure 1: Drawing of SHT20 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
SHT20 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/SHT20.
For more information please contact Sensirion via
info@sensirion.com.
For SHT20 two Evaluation Kits are available: EK-H4, a
four-channel device with Viewer Software, that also serves
for data-logging, and a simple EK-H5 directly connecting
one sensor via USB port to a computer.
1.0
1.0
2.4
0.3
0.4
1.5
0.4
0.75
1.1
0.2
SCL
SDA
NC
NC
VSS
VDD
SHT20
D0AC4
3.0
2.2
1.4 max
3.0
0.3 typ
2.4 max
Product Summary
The SHT20 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
SHT2can 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 4 – May 2014 2/14
Sensor Performance
Relative Humidity
1234
Parameter
Condition
Value
Units
Resolution 1
12 bit
0.04
%RH
8 bit
0.7
%RH
Accuracy
tolerance 2
typ
3.0
%RH
max
see Figure 2
%RH
Repeatability
0.1
%RH
Hysteresis
1
%RH
Nonlinearity
<0.1
%RH
Response time 3
63%
8
s
Operating Range
extended 4
0 to 100
%RH
Long Term Drift 5
Typ.
< 0.25
%RH/yr
Figure 2 Typical and maximal tolerance at 25°C for relative
humidity. For extensive information see Users Guide, Sect. 1.2.
Electrical Specification
Parameter
Condition
min
typ
max
Units
Supply Voltage, VDD
2.1
3.0
3.6
V
Supply Current, IDD 6
sleep mode
0.15
0.4
µA
measuring
200
300
330
µA
Power Dissipation 6
sleep mode
0.5
1.2
µW
measuring
0.6
0.9
1.0
mW
average 8bit
3.2
µW
Heater
VDD = 3.0 V
5.5mW, T = + 0.5-1.5°C
Communication
digital 2-wire interface, I2C protocol
Table 1 Electrical specification. For absolute maximum
values see Section 4.1 of Users Guide.
1
Default measurement 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.
Temperature
567
Parameter
Condition
Value
Units
Resolution 1
14 bit
0.01
°C
12 bit
0.04
°C
Accuracy
tolerance 2
typ
0.3
°C
max
see Figure 3
°C
Repeatability
0.1
°C
Operating Range
extended 4
-40 t0 125
°C
Response Time 7
63%
5 to 30
s
Long Term Drift8
Typ.
< 0.02
°C/yr
Figure 3 Typical and maximal tolerance for temperature sensor
in °C.
Packaging Information
Sensor Type
Packaging
Quantity
Order Number
SHT20
Tape & Reel
1500
1-100706-01
Tape & Reel
5000
1-100704-01
This datasheet is subject to change and may be amended
without prior notice.
5
Typical value for operation in normal RH/T operating range. Max. value is < 0.5
%RH/y. Value may be higher in environments with vaporized solvents, out-
gassing tapes, adhesives, packaging materials, etc. For more details please
refer to Handling Instructions.
6
Min and max values of Supply Current and Power Dissipation are based on
fixed VDD = 3.0V and T<60°C. The average value is based on one 8bit
measurement per second.
7
Response time depends on heat conductivity of sensor substrate.
8
Max. value is < 0.04°C/y.
± 0
± 2
± 4
± 6
± 8
± 10
010 20 30 40 50 60 70 80 90 100
ΔRH (%RH)
Relative Humidity (%RH)
maximum accuracy
typical accuracy
± 0.0
± 0.5
± 1.0
± 1.5
± 2.0
-40 -20 0 20 40 60 80 100 120
ΔT (C)
Temperature (°C)
maximum accuracy
typical accuracy
Datasheet SHT20
www.sensirion.com Version 4 – May 2014 3/14
Users Guide SHT20
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.
.
Figure 5 Typical accuracy of relative humidity measurements
given in %RH for temperatures 0 – 80°C.
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.
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.
Figure 6 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.
Figure 7 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).
100 ±4.5 ±4 ±4 ±4 ±4 ±4 ±4.5 ±5 ±5
90 ±4.5 ±4 ±3.5 ±3.5 ±3.5 ±3.5 ±4 ±4.5 ±5
80 ±4 ±3.5 ±3 ±3 ±3 ±3.5 ±3.5 ±4 ±4.5
70 ±4 ±3.5 ±3 ±3 ±3 ±3 ±3.5 ±3.5 ±4
60 ±3.5 ±3 ±3 ±3 ±3 ±3 ±3 ±3.5 ±3.5
50 ±3.5 ±3 ±3 ±3 ±3 ±3 ±3 ±3 ±3.5
40 ±3.5 ±3 ±3 ±3 ±3 ±3 ±3 ±3 ±3
30 ±3.5 ±3 ±3 ±3 ±3 ±3 ±3 ±3 ±3
20 ±3.5 ±3.5 ±3 ±3 ±3 ±3 ±3 ±3 ±3
10 ±4 ±4 ±3.5 ±3.5 ±3.5 ±3.5 ±3.5 ±3.5 ±3.5
0 ±4.5 ±4.5 ±4 ±4 ±4 ±4 ±4 ±4 ±4
010 20 30 40 50 60 70 80
Relative Humidity [%RH]
Temperature [°C]
0
1
2
3
4
5
6
7
8
020 40 60 80 100 120
Supply Current IDD (μA)
Temperature (°C)
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 Current IDD (nA)
Supply Voltage (VDD)
0
10
20
30
40
50
60
70
80
90
100
-40 -20 0 20 40 60 80 100 120
Relative Humidity (%)
Temperature (°C)
Max.
Range
Normal
Range
Datasheet SHT20
www.sensirion.com Version 4 – 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) 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
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.
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.
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
11
Solder types are related to the solder particle size in the paste: Type 3 covers
the size range of 25 – 45 µm (powder type 42).
1.0
1.0
0.3
0.4
1.5
0.4
0.7
0.2
0.2
2.4
Temperature
Time
tP
TP
TL
TS (max)
tL
preheating
critical zone
Datasheet SHT20
www.sensirion.com Version 4 – May 2014 5/14
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
12
.
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.
12
For example, 3M antistatic bag, product “1910” with zipper.
Figure 10 Top view of example of mounted SHT2x with slits
milled into PCB to minimize heat transfer.
2.4 Light
The SHT2x is not light sensitive. Prolonged direct
exposure to sunshine or strong UV radiation may age the
sensor.
2.5 Materials Used for Sealing / Mounting
Many materials absorb humidity and will act as a buffer
increasing response times and hysteresis. Materials in the
vicinity of the sensor must therefore be carefully chosen.
Recommended materials are: Any metals, 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 SHT20
www.sensirion.com Version 4 – May 2014 6/14
3 Interface Specifications
Pin
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 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
RP
SCL OUT
SDA OUT
SDA IN
SCL IN
C = 100nF
SHT2x
(slave)
1
6
5
2
4
3
Datasheet SHT20
www.sensirion.com Version 4 – 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
SHT20 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/SHT20.
Please note that in case VDD is set to 0 V (GND), e.g. in
case of a power off of the SHT2x, the SCL and SDA pads
are also pulled to GND. Consequently, the I2C bus is
blocked while VDD of the SHT2x is set to 0 V.
5.1 Start Up Sensor
As a first step, the sensor is powered up to the chosen
supply voltage VDD (between 2.1V 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.
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 SHT20
www.sensirion.com Version 4 – 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
Hold master or no hold master modes are explained in
next Section.
5.4 Hold / No Hold Master Mode
There are two different operation modes to communicate
with the 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 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
0
0
0
0
0
0
ACK
1
1
1
0
0
1
0
1
ACK
I2C address + write
Command (see Table 6)
19
20
21
22
23
24
25
26
27
S
1
0
0
0
0
0
0
1
ACK
Measurement
I2C address + read
Hold during measurement
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
0
1
1
0
0
0
1
1
ACK
0
1
0
1
0
0
1
0
ACK
Data (MSB)
Data (LSB)
Stat.
46
47
48
49
50
51
52
53
54
0
1
1
0
0
1
0
0
NACK
P
Checksum
Figure 15 Hold master communication sequence – grey blocks
are controlled by SHT2x. Bit 45 may be changed to NACK
followed by Stop condition (P) to omit checksum transmission.
In no hold master mode, the 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
0
0
0
0
0
0
ACK
1
1
1
1
0
1
0
1
ACK
wait
P
I2C address + write
Command (see Table 6)
20µs
19
20
21
22
23
24
25
26
27
Measurement
S
1
0
0
0
0
0
0
1
NACK
P
measuring
I2C address + read
19
20
21
22
23
24
25
26
27
Measurement
S
1
0
0
0
0
0
0
1
ACK
continue measuring
I2C address + read
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
0
1
1
0
0
0
1
1
ACK
0
1
0
1
0
0
1
0
ACK
Data (MSB)
Data (LSB)
Stat.
46
47
48
49
50
51
52
53
54
0
1
1
0
0
1
0
0
NACK
P
Checksum
Figure 16 No Hold master communication sequence – grey
blocks are controlled by SHT2x. If measurement is not
completed upon “read” command, 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 SHT20
www.sensirion.com Version 4 – 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
0
0
0
0
0
0
ACK
1
1
1
1
1
1
1
0
ACK
P
I2C address + write
Soft Reset
Figure 17 Soft Reset – grey blocks are controlled by SHT2x.
5.6 User Register
The 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
11 bit
‘00’
6
1
Status: End of battery13
‘0’: VDD > 2.25V
‘1’: VDD < 2.25V
‘0’
3, 4, 5
3
Reserved
2
1
Enable on-chip heater
‘0’
1
1
Disable OTP Reload
‘1’
Table 8 User Register. Cut-off value for End of Battery signal
may vary by ±0.1V. Reserved bits must not be changed. “OTP
reload” = ‘0’ 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
0
0
0
0
0
0
ACK
1
1
1
0
0
1
1
1
ACK
I2C address + write
Read Register
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
S
1
0
0
0
0
0
0
1
ACK
0
0
0
0
0
0
1
0
NACK
I2C address + read
Register content
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
S
1
0
0
0
0
0
0
0
ACK
1
1
1
0
0
1
1
0
ACK
I2C address + write
Write Register
55
56
57
58
59
60
61
62
63
0
0
0
0
0
0
1
1
ACK
P
Register content to be written
Figure 18 Read and write register sequence – grey blocks are
controlled by SHT2x. In this example, the resolution is set to 8bit
/ 12bit.
5.7 CRC Checksum
SHT2x 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”.
13
This status bit is updated after each measurement
Datasheet SHT20
www.sensirion.com Version 4 – May 2014 10/14
5.8 Serial Number
SHT20 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/SHT20.
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
i
w
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
14
.
Environment
Standard
Results15
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. 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
frame at diced edge is not covered with respective
protective coating. The total weight of the sensor is 25mg.
14
Temperature range is -40 to 125°C (AEC-Q100 temperature grade 1).
15
According to accuracy and long term drift specification given on Page 2.
Datasheet SHT20
www.sensirion.com Version 4 – May 2014 11/14
8.2 Filter Cap and Sockets
For SHT2x a filter cap SF2 will 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
(SHT20). 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 SHT20. 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 (20 for SHT20),
O = Output mode (D = Digital, P = PWM, S = SDM), 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 1500 and 5000 units per reel. For SHT20, 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
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
SHT20
D0AC4
Lot No.: XXO-NN-YRRRTTTTT
Quantity: RRRR
RoHS: Compliant
Lot No.
8.0
2.0
4.0
0.3
1.3
R0.3 MAX
R0.25
Ø1.5 MIN
Ø1.5 MIN
3.3
0.25
3.3
1.75
5.5
12.0
Datasheet SHT20
www.sensirion.com Version 4 – 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.
www.sensirion.com Version 4 – May 2014 13/14
Revision History
Date
Version
Page(s)
Changes
6 May 2009
0.3
1 – 9
Initial preliminary release
21 January 2010
1.0
1 – 4, 7 – 10
Complete revision. For complete revision list please require respective document.
5 May 2010
1.1
1 – 12
Typical specification for temperature sensor. Elimination of errors. For detailed
information, please require complete change list at info@sensirion.com.
31 May 2011
2
1 – 7, 10 –
13
Updated temperature accuracy specifications, MSL and standards. Elimination of
errors. For detailed information, please require complete change list at
info@sensirion.com.
December 2011
3
1, 7-10
Tolerance of threshold value for low battery signal, minor text adaptations and
corrections.
May 2014
4
1-4, 7-8, 9-10
Sensor window dimension updated, several minor adjustments
Datasheet SHT20
www.sensirion.com Version 4 – 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.
Copyright © 2014, by SENSIRION.
CMOSens® is a trademark of Sensirion
All rights reserved
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