SHT21P SENSIRION, SHT21P Datasheet - Page 5

• Manufacturer Part Number: SHT21P
• Description: SENSOR, HUMIDITY & TEMP
• Manufacturer: SENSIRION

Specifications of SHT21P

• Humidity Range: 0 - 100% RH
• Sensor Output: Analogue - PWM Interface
• Sensor Terminals: SMD
• Response Time: 8s
• Supply Voltage Range: 2.1V To 3.6V
• Accuracy: 2% RH
• Supply Voltage: 3VDC
• Termination: RoHS Compliant
• Capacitance: 0µF
• Rohs Compliant: Yes
• Sensing Accuracy: 2%
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 2 - 1 Year

Datasheet SHT21P
rest of the PCB or milling a slit into the PCB around the
sensor – see Figure 8.
Figure 8 Top view of example of mounted SHT2x with slits
milled into PCB to minimize heat transfer.
2.5
The SHT2x is not light sensitive. Prolonged direct
exposure to sunshine or strong UV radiation may age the
sensor.
2.6
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.
2.7
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.
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Materials Used for Sealing / Mounting
Wiring Considerations and Signal Integrity
Version 1.1 – May 2010
3 Interface Specifications
Table 2 SHT21P pin assignment (top view)
3.1
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.
3.2
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.
Figure 9 Typical application circuit, including decoupling of
VDD and VSS by a capacitor.
3.3
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.
4 Electrical Characteristics
4.1
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).
Pin Name
3,4
1
2
5
6
VDD Supply Voltage
SDA Data bit-stream
VSS Ground
SCL Selector for RH or T
Power Pins (VDD, VSS)
SCL – Output Selector Pad
SDA – Bit Stream Pad
Absolute Maximum Ratings
NC
Not connected
PWM bit stream
Select RH or T
Comment
SDA
VDD
VSS
SCL
4
5
6
SHT2x
3
2
1
5/9