Datasheet
Datasheet SHT21
www.sensirion.com Version 4 – May 2014 10/14
5.8 Serial Number
SHT21 provides an electronic identification code. For
instructions on how to read the identification code please
refer to the Application Note “Electronic Identification
Code” – to be downloaded from the web page
www.sensirion.com/SHT21.
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 S
RH
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 RH
i
the values need to be transformed from
relative humidity above water RH
w
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
expexp
Units are %RH for relative humidity and °C for
temperature. The corresponding coefficients are defined
as follows: β
w
= 17.62, λ
w
= 243.12°C, β
i
= 22.46, λ
i
=
272.62°C.
6.2 Temperature Conversion
The temperature T is calculated by inserting temperature
signal output S
T
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
16
.
Environment
Standard
Results
17
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 T
amb
= 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
16
Temperature range is -40 to 125°C (AEC-Q100 temperature grade 1).
17
According to accuracy and long term drift specification given on Page 2.