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SHT15

P1-P3P4-P6P7-P9P10-P12
Datasheet SHT1x
www.sensirion.com Version 5 – December 2011 7/12
Communication terminates after the acknowledge bit of
the CRC data. If CRC-8 checksum is not used the
controller may terminate the communication after the
measurement data LSB by keeping ACK high. The device
automatically returns to Sleep Mode after measurement
and communication are completed.
Important: To keep self heating below 0.1°C, SHT1x
should not be active for more than 10% of the time – e.g.
maximum one measurement per second at 12bit accuracy
shall be made.
3.4 Connection reset sequence
If communication with the device is lost the following signal
sequence will reset the serial interface: While leaving
DATA high, toggle SCK nine or more times – see Figure
13. This must be followed by a Transmission Start
sequence preceding the next command. This sequence
resets the interface only. The status register preserves its
content.
Figure 13: Connection Reset Sequence
3.5 CRC Checksum calculation
The whole digital transmission is secured by an 8bit
checksum. It ensures that any wrong data can be detected
and eliminated. As described above this is an additional
feature of which may be used or abandoned. Please
consult Application Note “CRC Checksum” for information
on how to calculate the CRC.
3.6 Status Register
Some of the advanced functions of the SHT1x such as
selecting measurement resolution, end-of-battery notice,
use of OTP reload or using the heater may be activated by
sending a command to the status register. The following
section gives a brief overview of these features.
After the command Status Register Read or Status
Register Write – see Table 4 – the content of 8 bits of the
status register may be read out or written. For the
communication compare Figure 14 and Figure 15 – the
assignation of the bits is displayed in Table 5.
TS
ACK
Bit 7
ACK
0
0
0
0
0
1
1
0
Status Register
Figure 14: Status Register Write
Figure 15: Status Register Read
Examples of full communication cycle are displayed in
Figure 16 and Figure 17.
TS
Wait for
DATA ready
ACK
0
0
0
Command
0
0
MSB
LSb
ACK
ACK
LSB
Checksum
Figure 16: Overview of Measurement Sequence. TS = Trans-
mission Start, MSB = Most Significant Byte, LSB = Last
Significant Byte, LSb = Last Significant Bit.
Figure 17: Example RH measurement sequence for value “0000’0100“0011’0001” = 1073 = 35.50%RH (without temperature
compensation). DATA valid times are given and referenced in boxes on DATA line. Bold DATA lines are controlled by sensor while plain
lines are controlled by the micro-controller.
TS
ACK
Bit 7
ACK
Bit 7
ACK
0
0
0
0
0
1
1
1
Status Register
Checksum
DATA
SCK
80%
2
0%
80%
2
0%
1
2
3
2
4 - 8
9
Transmission Start
DATA
DATA
SCK
SCK
SCK
DATA
A2
A1
A0
C4
C3 C2 C1
C0 ACK
15 14 13 12 11 10 9 8 ACK 7 6 5 4 3 2 1 0 ACK
7 6
5 4
3
2 1 0
ACK
Transmission Start
Address = ‘000
’
Command = ‘00101
’
12bit Humidity Data
CRC
-
8 Checksum
Transmission Start
Measurement
(80ms for 12bit)
Sleep
(wait for next
measurement)
Idle Bits
Skip ACK to end trans
mission
(if
no CR
C is used)
Sensor pulls DATA line low after
completion of measurement
MSb
LSb
MSb
LSb
15
14
13 12
11
10
9 8
ACK
7 6 5 4 3 2 1
0
A2
A1
A0
C4
C3
C2
C1
C0
ACK
7 6 5 4 3 2 1 0 ACK
ACK
Datasheet SHT1x
www.sensirion.com Version 5 – December 2011 8/12
Bit
Type
Description
Default
7
reserved
0
6 R
End of Battery (lo
w voltage
detection)
‘0’ for VDD > 2.47
‘1’ for VDD < 2.47
X
No default value,
bit is only updated
after a
measurement
5
reserved
0
4
reserved
0
3
For Testing only, do not use
0
2
R/W
Heater
0
off
1
R/W
no reload from OTP
0
reload
0 R/W
’1’ = 8bit RH / 12bit Temp.
resolution
’0’ = 12bit RH / 14bit Temp.
resolution
0
12bit RH
14bit Temp.
Table 5: Status Register Bits
Measurement resolution: The default measurement
resolution of 14bit (temperature) and 12bit (humidity) can
be reduced to 12 and 8bit. This is especially useful in high
speed or extreme low power applications.
End of Battery function detects and notifies VDD voltages
below 2.47V. Accuracy is ±0.05V.
Heater: An on chip heating element can be addressed by
writing a command into status register. The heater may
increase the temperature of the sensor by 5 – 10°C
12
beyond ambient temperature. The heater draws roughly
8mA @ 5V supply voltage.
For example the heater can be helpful for functionality
analysis: Humidity and temperature readings before and
after applying the heater are compared. Temperature shall
increase while relative humidity decreases at the same
time. Dew point shall remain the same.
Please note: The temperature reading will display the
temperature of the heated sensor element and not
ambient temperature. Furthermore, the sensor is not
qualified for continuous application of the heater.
OTP reload: With this operation the calibration data is
uploaded to the register before each measurement. This
may be deactivated for reducing measurement time by
about 10ms.
4 Conversion of Signal Output
4.1 Relative Humidity
For compensating non-linearity of the humidity sensor –
see Figure 18 – and for obtaining the full accuracy of the
sensor it is recommended to convert the humidity readout
12
Corresponds to 9 – 18°F
(SO
RH
) with the following formula with coefficients given in
Table 6:
2
RH3RH21linear
SOcSOccRH ⋅+⋅+=
(%RH)
SO
RH
c
1
c
2
c
3
12 bit
-
2.0468
0.0367
-
1.5955
E
-
6
8 bit
-
2.0468
0.5872
-
4.0845
E
-
4
Table 6: Humidity conversion coefficients
Values higher than 99% RH indicate fully saturated air and
must be processed and displayed as 100%RH
13
. Please
note that the humidity sensor has no significant voltage
dependency.
0%
20%
40%
60%
80%
100%
0 500 1000 1500 2000 2500 3000 3500
SO
RH
sensor readout (12bit)
Relative Humidity
Figure 18: Conversion from SO
RH
to relative humidity
4.2 Temperature compensation of Humidity Signal
For temperatures significantly different from 25°C (~77°F)
the humidity signal requires temperature compensation.
The temperature correction corresponds roughly to
0.12%RH/°C @ 50%RH. Coefficients for the temperature
compensation are given in Table 7.
(
)
(
)
linearRH21Ctrue
RHSOtt25TRH +⋅+⋅−=
°
SO
RH
t
1
t
2
12 bit
0.01
0.00008
8 bit
0.01
0.00128
Table 7: Temperature compensation coefficients
4.3 Temperature
The band-gap PTAT (Proportional To Absolute
Temperature) temperature sensor is very linear by design.
Use the following formula to convert digital readout (SO
T
)
to temperature value, with coefficients given in Table 8:
T21
SOddT ⋅+=
13
If wetted excessively (strong condensation of water on sensor surface),
sensor output signal can drop below 100%RH (even below 0%RH in some
cases), but the sensor will recover completely when water droplets
evaporate. The sensor is not damaged by water immersion or condensation.
Datasheet SHT1x
www.sensirion.com Version 5 – December 2011 9/12
VDD
d
1
(°C)
d
1
(°F)
SO
T
d
2
(°C)
d
2
(°F)
5V
-
40.1
-
40.2
14bit
0.01
0.018
4V
-
39.
8
-
39.
6
12bit
0.04
0.072
3.5V
-
39.
7
-
39.
5
3V
-
39.6
-
39.3
2.5V
-
39.
4
-
38.9
Table 8: Temperature conversion coefficients.
4.4 Dew Point
SHT1x is not measuring dew point directly, however dew
point can be derived from humidity and temperature
readings. Since humidity and temperature are both
measured on the same monolithic chip, the SHT1x allows
superb dew point measurements.
For dew point (T
d
) calculations there are various formulas
to be applied, most of them quite complicated. For the
temperature range of -40 – 50°C the following
approximation provides good accuracy with parameters
given in Table 9:
( )
TT
Tm
100%
RH
lnm
TT
Tm
100%
RH
ln
TTRH,T
n
n
nd
+
⋅
−
−
+
⋅
+
⋅=
Temperature Range
Tn (°C)
m
Above water,
0
–
50°C
243.12
17.62
Above ice,
-
40
–
0°C
272.62
22.46
Table 9: Parameters for dew point (T
d
) calculation.
Please note that “ln(…)” denotes the natural logarithm. For
RH and T the linearized and compensated values for
relative humidity and temperature shall be applied.
For more information on dew point calculation see
Application Note “Introduction to Humidity”.
5 Environmental Stability
If sensors are qualified for assemblies or devices, please
make sure that they experience same conditions as the
reference sensor. It should be taken into account that
response times in assemblies may be longer, hence
enough dwell time for the measurement shall be granted.
For detailed information please consult Application Note
“Qualification Guide”.
The SHT1x sensor series were tested according to AEC-
Q100 Rev. G qualification test method. Sensor
specifications are tested to prevail under the AEC-Q100
temperature grade 2 test conditions listed in Table 10
14
.
Sensor performance under other test conditions cannot be
guaranteed and is not part of the sensor specifications.
Especially, no guarantee can be given for sensor
performance in the field or for customer’s specific
application.
Please contact Sensirion for detailed information.
Environment
Standard
Results
15
HTSL
125°C, 1000
hours
Within
specifications
TC
-
50°C
-
125°C, 1000 cycles
Acc. JESD22-A104-C
Within
specifications
UHST
130°C / 85%RH
/
≈2.3bar
,
96h
Within
specifications
TH
U
85°C / 85%RH, 1000h
Within
specifications
ESD immunity
MIL STD 883E, method 3015
(Human Body Model at ±2kV)
Qualified
Latch
-
up
force current of ±100mA with
T
amb
= 80°C, acc. JEDEC 17
Qualified
Table 10: Qualification tests: HTSL = High Temperature Storage
Lifetime, TC = Temperature Cycles, UHST = Unbiased Highly
accelerated Stress Test, THB = Temperature Humidity Unbiased
6 Packaging
6.1 Packaging type
SHT1x are supplied in a surface mountable LCC
(Leadless Chip Carrier) type package. The sensor housing
consists of a Liquid Crystal Polymer (LCP) cap with epoxy
glob top on a standard 0.8mm FR4 substrate. The device
is fully RoHS and WEEE compliant – it is free of Pb, Cd,
Hg, Cr(6+), PBB and PBDE.
Device size is 7.47 x 4.93 x 2.5 mm (0.29 x 0.19 x 0.1
inch), see Figure 1, weight is 100 mg.
6.2 Traceability Information
All SHT1x are marked with an alphanumeric, three digit
code on the chip cap – see “A5Z” on Figure 1. The lot
numbers allow full traceability through production,
calibration and testing. No information can be derived from
the code directly; respective data is stored at Sensirion
and is provided upon request.
Labels on the reels are displayed in Figures 19 and 20,
they both give traceability information.
14
Sensor operation temperature range is -40 to 105°C according to AEC-Q100
temperature grade 2.
15
According to accuracy and long term drift specification given on Page 2.
P1-P3P4-P6P7-P9P10-P12

SHT15

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Board Mount Humidity Sensors Humid & Temp Sensor
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