Datasheet SHT21S
www.sensirion.com Version 4 – May 2014 7/10
6 Conversion of Signal Output
After the low pass filter the sensor provides an output
Voltage V
SO
which as a portion of VDD then is converted
into a physical value.
Resolution is set to 10 bit for relative humidity and 12 bit
for temperature and cannot be changed. The sensor
reading is linearized and hence it can be converted to a
physical value by an easy linear equation.
6.1 Relative Humidity Conversion
With the relative humidity signal output the relative
humidity RH is obtained by the following formula (result in
%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 a certain temperature
t. The equation is given in the following, compare also
Application Note “Introduction to Humidity”:
tλ
tβ
exp
tλ
tβ
expRHRH
i
i
w
w
wi
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):
VDD
V
175.7246.85T
SO
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
5
.
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
Sensor operation temperature range is -40 to 125°C (AEC-Q100 temperature
grade 1).
performance in the field or for customer’s specific
application.
-50°C - 125°C, 1000 cycles
130°C / 85%RH / ≈2.3bar, 96h
HBM 4kV, MM 200V, CDM
750V/500V (corner/other pins)
force current of ±100mA with T
amb
= 125°C
Table 5: Qualification tests: 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.
If sensors are qualified for reliability and behavior in
extreme conditions, please make sure that they
experience same conditions as the reference sensor. It
should be taken into account that response times in
assemblies may be longer, hence enough dwell time for
the measurement shall be granted. For detailed
information please consult Application Note “Qualification
Guide”.
8 Packaging
8.1 Packaging type
SHT2x sensors are provided in DFN packaging (in
analogy with QFN packaging). DFN stands for Dual Flat
No leads.
The sensor chip is mounted to a lead frame made of Cu
and plated with Ni/Pd/Au. Chip and lead frame are over
molded by green epoxy-based mold compound. Please
note that side walls of sensors are diced and hence lead
frame at diced edge is not covered with respective
protective coating. The total weight of the sensor is 25mg.
8.2 Filter Cap and Sockets
For SHT2x a filter cap SF2 is available. It is designed for
fast response times and compact size. Please find the
datasheet on Sensirion’s web page.
According to accuracy and long term drift specification given on Page 2.
