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SHT20P Datasheet(PDF) 6 Page - List of Unclassifed Manufacturers

Part No. SHT20P
Description  DFN type package reflow solderable
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Maker  ETC2 [List of Unclassifed Manufacturers]
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SHT20P Datasheet(HTML) 6 Page - List of Unclassifed Manufacturers

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Datasheet SHT20P
www.sensirion.com
Version 4 – May 2014
6/10
Parameter
min
max
Units
VDD to VSS
-0.3
5
V
Digital IO Pins (SDA, SCL)
to VSS
-0.3
VDD + 0.3
V
Input Current on any Pin
-100
100
mA
Table 3 Electrical absolute maximum ratings
ESD immunity is qualified according to JEDEC JESD22-
A114 method (Human Body Model at
4kV), JEDEC
JESD22-A115 method (Machine Model
200V) and ESDA
ESD-STM5.3.1-1999 and AEC-Q100-011 (Charged
Device Model, 750V corner pins, 500V other pins). Latch-
up immunity is provided at a force current of
100mA with
Tamb = 125°C according to JEDEC JESD78. For exposure
beyond named limits the sensor needs additional
protection circuit.
3.2
Input / Output Characteristics
The electrical characteristics such as power consumption,
low and high level input and output voltages depend on
the supply voltage. For proper communication with the
sensor it is essential to make sure that signal design is
strictly within the limits given in Table 4.
Parameter
min
typ
max Units
Output Low Voltage, VOL
0
V
Output High Voltage, VOH
VDD
V
Output Sink Current, IOL
40
µA
Table 4 DC characteristics of output pad. VDD = 2.1 V to 3.6 V,
T = -40 °C to 125 °C, unless otherwise noted.
4 Communication with Sensor
4.1
Start up Sensor
As a first step, the sensor is powered up to VDD (between
2.1V and 3.6V). After power-up, the sensor needs at most
150ms for reaching idle state. During that time SDA is in
undefined state. Then the sensor starts measuring and
providing data on PWM bit-stream.
4.2
PWM Specification
Pulse Width Modulation runs on a constant frequency and
the measured information is provided as duty cycle on that
frequency – see Figure 10. Such information is measured
humidity for SCL pulled high and temperature for SCL
pulled low.
Figure 10 PWM signal. Base frequency runs constantly at
approximately 120 Hz, hence tF is about 8.3ms. The signal is
provided on tPW as a ratio of tF.
The measured data – either humidity or temperature – is
provided as ratio of tPW and tF. tPW shall always be given as
ratio of tF to make it independent of variations of the base
frequency.
5 Conversion of Signal Output
Resolution is set to 10 bit relative humidity and 12 bit
temperature reading and cannot be changed. The sensor
reading is linear and hence it can be converted to a
physical value by an easy linear equation.
5.1
Relative Humidity Conversion
With the relative humidity signal output the relative
humidity RH is obtained by the following formula (result in
%RH):
F
PW
t
t
125
6
RH
The physical value RH given above corresponds to
the relative humidity above liquid water according to
World Meteorological Organization (WMO). For
relative humidity values above ice RHi the values need to
be transformed as from relative humidity above water RHw
at a certain temperature t follows – compare also
Application Note “Introduction to Humidity”:




t
λ
t
β
exp
t
λ
t
β
exp
RH
RH
i
i
w
w
w
i
Units are %RH for relative humidity and °C for
temperature. The corresponding coefficients are defined
as follows: βw = 17.62, λw = 243.12°C, βi = 22.46, λi =
272.62°C.
5.2
Temperature Conversion
The temperature T is calculated by inserting the ratio of
tPW and tF into the following formula (result in °C):
F
PW
t
t
175.72
46.85
T
SDA
VDD
0V
tF
tPW


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