Datasheet SHT7x
www.sensirion.com Version 5 – December 2011 7/12
Figure 12: 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.
Bit
Type
Description
Default
7
reserved
0
6 R
End of Battery (low 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 2.47 V. Accuracy is ±0.05 V.
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.
12
Corresponds to 9 – 18°F
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 13 and for obtaining the full accuracy of the
sensor it is recommended to convert the humidity readout
(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
-
1.5955E
-
6
8 bit
-
2.0468
0.5872
-
4.0845E
-
4
Table 6: Humidity conversion coefficients
DATA
DATA
SCK
SCK
SCK
DATA
A2 A1
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 CRC 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 SHT7x
www.sensirion.com Version 5 – December 2011 8/12
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.
Figure 13: 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 8.
(
)
(
)
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 9:
T21
SOddT +=
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.
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.
4.4 Dew Point
SHT7x 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 SHT7x 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 10:
( )
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
“Testing Guide”.
SHT7x have been tested according to the test conditions
given in Table 11. 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.
0%
20%
40%
60%
80%
100%
0 500 1000 1500 2000 2500 3000 3500
Relative Humidity
SORH sensor readout (12bit)
Datasheet SHT7x
www.sensirion.com Version 5 – December 2011 9/12
E
nvironment
Standard
Results
14
HTOL
125°C, 1000 h
Within
specifications
TC
-
40°C
-
125°C, 500 cycles
Acc. JESD22-A104-C
Within
specifications
THU
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
Qualif
ied
Table 10: Qualification tests: HTSL = High Temperature Storage
Lifetime, TC = Temperature Cycles, UHST = Unbiased Highly
accelerated temperature and humidity Test, THU = Temperature
humidity unbiased
6 Packaging
6.1 Packaging type
The device is supplied in a single-in-line pin type package.
The sensor housing consists of a Liquid Crystal Polymer
(LCP) cap with epoxy glob top on a standard 0.6 mm FR4
substrate. The sensor head is connected to the pins, by a
small bridge to minimize heat conduction and response
times. The pins are made of Cu/Be alloy coated with
1.3µm Ni and 0.5µm Au, which are soldered to the FR4
substrate by lead-free solder paste. The gold plated back
side of the sensor head is connected to the GND pin. A
100nF capacitor is mounted on the back side between
VDD and GND. The device is fully RoHS and WEEE
compliant thus it is free of of Pb, Cd, Hg, Cr(6+), PBB
and PBDE.
Size including pins is 19.5 x 5.08 x 3.1mm. Total weight:
168 mg, weight of sensor head: 73 mg.
All pins are Au plated to avoid corrosion. They can be
soldered or mate with most 1.27 mm (0.05’’) sockets, for
example: Preci-dip / Mill-Max R851-83-004-20-001 or
similar.
6.2 Traceability Information
All SHT7x are marked with an alphanumeric, three digit
code on the chip cap see “B2G” 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.
Labels on the reels are displayed in Figure 14 and Figure
15, they both give traceability information.
14
According to accuracy and long term drift specification given on Page 2.
Figure 14: First label on reel: XX = Sensor Type (71 for SHT71),
NN = Chip Version (04 for V4), Y = last digit of year, RRR =
number of sensors on reel divided by 10 (200 for 2000 units),
TTTTT = Traceability Code.
Figure 15: Second label on reel: For Device Type and Part
Order Number please refer to Table 12, Delivery Date (also
Date Code) is date of packaging of sensors (DD = day, MM =
month, YYYY = year), CCCC = number of order.
6.3 Shipping Package
SHT7x are shipped in 32mm tape at 50pcs each for
details see Figure 16 and Table 12. Reels are individually
labeled with barcode and human readable labels, see
section 6.2.
Sensor Type
Packaging
Quantity
Order
Number
SHT71
Tape Stripes
50
1
-
100092
-
04
SHT75
Tape Stripes
50
1
-
100071
-
04
Table 11: Packaging types per sensor type.
Dimensions of packaging tape are given in Figure 16. All
tapes have a 7 pockets empty leader tape (first pockets of
the tape) and a 7 pockets empty trailer tape (last pockets
of the tape).
Device Type: 1-100PPP-NN
Description: Humidity & Temperature Sensor
SHTxx
Part Order No. 1-100PPP-NN or Customer Number
Date of Delivery: DD.MM.YYYY
Order Code: 45CCCC / 0
Lot No.: XX0-NN-YRRRTTTTT
Quantity: RRRR
RoHS: Compliant
Lot No.

SHT71

Mfr. #:
Manufacturer:
Sensirion
Description:
Board Mount Humidity Sensors Humid & Temp Sensor
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union

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