SHT21P Datasheet PDF - Sensirion
|Description||Humidity and Temperature Sensor IC|
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Humidity and Temperature Sensor IC
Analog output, PWM interface
Low power consumption
Excellent long term stability
DFN type package – reflow solderable
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 Pulse Width Modulated (PWM) 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.
PWM signal runs on a base frequency of 120Hz, the data
signal is provided on SDA line. Pulling SCL high or low
allows for switching between humidity and temperature,
respectively. The sensor measures twice per second. The
PWM signal may be converted to an analog ratiometric
interface by adding a low pass filter.
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.
NC VDD SCL
NC VSS SDA
Figure 1: Drawing of SHT21P 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).
SHT21P 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
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 free of Pb, Cd
and Hg – hence it is fully RoHS and WEEE compliant.
Additional information such as Application Notes is
available from the web page www.sensirion.com/sht21.
For more information please contact Sensirion via
Version 4 – May 2014
Figure 8 Top view of example of mounted SHT2x with slits
milled into PCB to minimize heat transfer.
The SHT2x is not light sensitive. Prolonged direct
exposure to sunshine or strong UV radiation may age the
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,
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.
1 SDA Data bit-stream
2 VSS Ground
5 VDD Supply Voltage
6 SCL Selector for RH or T
3,4 NC Not connected
Table 2 SHT21P pin assignment (top view)
2.6 Power Pins (VDD, VSS)
The supply voltage of SHT21P 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 9.
2.7 SCL – Output Selector Pad
SCL is used to select humidity or temperature output. SCL
high yields humidity output, SCL low yields temperature
output. Please note that a change of SCL will affect the
output on SDA after maximal 1.2 seconds.
Select RH or T
PWM bit stream SDA
Figure 9 Typical application circuit, including decoupling of
VDD and VSS by a capacitor.
2.8 SDA – Bit Stream Pad
On SDA the sensor is providing PWM 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.
3 Electrical Characteristics
3.1 Absolute Maximum Ratings
The electrical characteristics of SHT21P 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).
Version 4 – May 2014
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|SHT21||The function is Humidity and Temperature Sensor.|
|SHT21||The function is Humidity and Temperature Sensor IC.|
|SHT21P||The function is Humidity and Temperature Sensor IC.|
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