SHT21P datasheet(5/10 Pages) ETC2

5 / 10 page

Datasheet SHT21P

www.sensirion.com

Version 4 – May 2014

5/10

Figure 8 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.

Interface Specifications

Pin Name

Comment

SDA Data bit-stream

VSS Ground

VDD Supply Voltage

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.

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).

SDA

SCL

VSS

VDD

SHT2x

PWM bit stream

Select RH or T

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