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SHT21S Datasheet PDF - Sensirion

Part Number SHT21S
Description Humidity and Temperature Sensor IC
Manufacturers Sensirion 
Logo Sensirion Logo 

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Datasheet SHT21S
Humidity and Temperature Sensor IC
Fully calibrated
SDM interface convertible to analog output
Low power consumption
Excellent long term stability
DFN type package reflow solderable
Product Summary
The SHT21 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 analog Sigma Delta Modulated (SDM) 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.
SDM signal is a pulse sequence that with a low pass filter
may be converted into analog voltage output. The data
signal is provided on SDA line. Pulling SCL high or low
allows for switching between humidity and temperature,
respectively. The sensor measures the physical values
twice per second.
Every sensor is individually calibrated and tested. Lot
identification is printed on the sensor.
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.
Dimensions
3.0
0.3 typ
1.4 max
2.2
0.4 0.3
2.4
1.1
Bottom
View
NC VDD SCL
1.0 1.0
NC VSS SDA
Figure 1: Drawing of SHT21S 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. Numbering of E/O pads starts at lower
right corner (indicated by notch in die pad) and goes clockwise
(compare Table 2).
Sensor Chip
SHT21S feature 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
Additional information such as Application Notes is
available from the web page www.sensirion.com/sht21.
For more information please contact Sensirion via
info@sensirion.com.
www.sensirion.com
Version 4 May 2014
1/10

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SHT21S equivalent
Datasheet SHT21S
Figure 9 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.
3 Interface Specifications
Pin Name
Comment
1 SDA Data bit-stream
2 VSS Ground
5 VDD Supply Voltage
6 SCL Selector for RH or T
3,4 NC Not connected
4
5
6
Table 2 SHT21S pin assignment (top view)
3
2
1
3.1 Power Pins (VDD, VSS)
The supply voltage of SHT21S 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 10.
3.2 SCL Output Selector Pad
SCL is used to select humidity or temperature output. SCL
high yields humidity output, SCL low yields temperature
output.
VDD
SCL
Select RH or T
SHT2x
SDM bit stream SDA
VSS
Figure 10 Typical application circuit, including decoupling of
VDD and VSS by a capacitor.
3.3 SDA Bit Stream Pad
On SDA the sensor is providing SDM output. The signal is
carrying humidity or temperature data depending on SCL
being high or low, respectively. See Table 4 for detailed
I/O characteristic of the sensor.
4 Electrical Characteristics
4.1 Absolute Maximum Ratings
The electrical characteristics of SHT21S 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).
www.sensirion.com
Version 4 May 2014
5/10


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