Datasheet SHT7x
(SHT71, SHT75)
Humidity and Temperature Sensor
•
•
•
•
•
Fully calibrated
Digital output
Low power consumption
Excellent long term stability
Pin type package – easy integration
Product Summary
SHT7x (including SHT71 and SHT75) is Sensirion’s family
of relative humidity and temperature sensors with pins.
The sensors integrate sensor elements plus signal
processing in compact format and provide a fully
calibrated digital output. A unique capacitive sensor
element is used for measuring relative humidity while
temperature is measured by a band-gap sensor. The
applied CMOSens® technology guarantees excellent
reliability and long term stability. Both sensors are
seamlessly coupled to a 14bit analog to digital converter
and a serial interface circuit. This results in superior signal
quality, a fast response time and insensitivity to external
disturbances (EMC).
Dimensions
3.1
3.7
2.2
Each SHT7x is individually calibrated in a precision
humidity chamber. The calibration coefficients are
programmed into an OTP memory on the chip. These
coefficients are used to internally calibrate the signals
from the sensors. The 2-wire serial interface and internal
voltage regulation allows for easy and fast system
integration. The small size and low power consumption
makes SHT7x the ultimate choice for even the most
demanding applications.
SHT7x is supplied on FR4 with pins which allows for easy
integration or replacement. The same sensor is also
available surface mountable packaging (SHT1x) or on flex
print (SHTA1).
Sensor Chip
SHT7x V4 – for which this datasheet applies – features a
version 4 Silicon sensor chip. Besides a humidity and a
temperature sensor the chip contains an amplifier, A/D
converter, OTP memory and a digital interface. V4 sensors
can be identified by the alpha-numeric traceability code on
the sensor cap – see example “B2G” code on Figure 1.
Material Contents
While the sensor is made of a CMOS chip the sensor
housing consists of an LCP cap with epoxy glob top on an
FR4 substrate. Pins are made of a Cu/Be alloy coated with
Ni and Au. The device is fully RoHS and WEEE compliant,
thus it is free of Pb, Cd, Hg, Cr(6+), PBB and PBDE.
Evaluation Kits
13.5
71
19.5
3.7
1.2
Ø 0.4
6.4
B2G
0.6
6.0
3.4
1 2 3 4
0.46
5.08
1.27
0.2
2.0
Figure 1:
Drawing of SHT7x (applies to SHT71 and SHT75)
sensor packaging, dimensions in mm (1mm = 0.039inch).
Contact assignment: 1: SCK, 2: VDD, 3: GND, 4: DATA.
Hatched item on backside of PCB is a 100nF capacitor – see
Section 2.1 for more information.
For sensor trial measurements, for qualification of the
sensor or even experimental application of the sensor
there is an evaluation kit
EK-H2
available including sensor,
hard and software to interface with a computer.
For more sophisticated and demanding measurements a
multi port evaluation kit
EK-H3
is available which allows for
parallel application of up to 20 sensors.
Version 4.1 – July 2008
Datasheet SHT7x
Sensor Performance
Relative Humidity
12
Parameter
Resolution
1
Accuracy
2
SHT71
Accuracy
2
SHT75
Repeatability
Replacement
Hysteresis
Nonlinearity
Response time
3
Operating Range
Long term drift
4
raw data
linearized
tau 63%
0
normal
< 0.5
typ
max
typ
max
Condition
min
0.5
8
typ
0.03
12
max
0.03
12
Units
%RH
bit
%RH
%RH
%RH
%RH
%RH
%RH
s
100 %RH
%RH/yr
Temperature
45
Parameter
Resolution
1
Accuracy
2
SHT71
Accuracy
2
SHT75
Repeatability
Replacement
Operating Range
Response Time
6
Long term drift
tau 63%
typ
max
typ
max
Condition
min
0.04
12
typ
0.01
14
max
0.01
14
Units
°C
bit
°C
°C
°C
°C
°F
s
°C/yr
±3.0
see Figure 2
±1.8
see Figure 2
±0.1
fully interchangeable
±1
±3
<<1
8
±0.4
see Figure 3
±0.3
see Figure 3
±0.1
fully interchangeable
-40
123.8
-40
254.9
5
30
< 0.04
±6
± 3.0
± 2.5
±4
∆
RH (%RH)
∆
T (°C)
SHT71
±2
SHT75
±0
± 2.0
± 1.5
± 1.0
± 0.5
± 0.0
0
10
20
30 40 50 60 70
Relative Humidity (%RH)
80
90
100
-40
-20
0
20
40
Temperature (°C)
60
80
100
SHT75
SHT71
Figure 2:
Maximal RH-tolerance at 25°C per sensor type.
Figure 3:
Maximal T-tolerance per sensor type.
Electrical and General Items
Parameter
Source Voltage
Power
Consumption
5
Communication
Storage
typ max Units
3.3
5.5
V
sleep
2
5
W
measuring
3
mW
average
150
W
digital 2-wire interface, see Communication
10 – 50°C (0 – 80°C peak), 20 – 60%RH
Condition
min
2.4
Packaging Information
Sensor Type
SHT71
SHT75
Packaging
Tape Stripes
Tape Stripes
Quantity
50
50
Order Number
1-100092-04
1-100071-04
4
1
The default measurement resolution of is 14bit for temperature and 12bit for
humidity. It can be reduced to 12/8bit by command to status register.
2
Accuracies are tested at Outgoing Quality Control at 25°C (77°F) and 3.3V.
Values exclude hysteresis and non-linearity.
3
Time for reaching 63% of a step function, valid at 25°C and 1 m/s airflow.
Value may be higher in environments with high contents of volatile organic
compounds. See Section 1.3 of Users Guide.
5
Values for VDD=5.5V at 25°C, average value at one 12bit measurement
per second.
6
Response time depends on heat capacity of and thermal resistance to
sensor substrate.
www.sensirion.com
Version 4.1 – July 2008
2/11
Users Guide SHT7x
1 Application Information
1.1 Operating Conditions
Sensor works stable within recommended normal range –
see Figure 4. Long term exposures to conditions outside
normal range may temporarily offset the RH signal (+3
%RH after 60h). After return to normal range it will slowly
return towards calibration state by itself. See Section 1.4.
“Reconditioning Procedure” to accelerate eliminating the
offset. Prolonged exposure to extreme conditions may
accelerate ageing.
Relative Humidity (%)
10°C – 50°C (0 – 80°C for limited time) and humidity at 20
– 60%RH (sensors that are not stored in ESD bags). For
sensors that have been removed from the original
packaging we recommend to stored them in ESD bags
made of PE-HD
8
.
In manufacturing and transport the sensors shall be
prevented of high concentration of chemical solvents and
long exposure times. Out-gassing of glues, adhesive tapes
and stickers or out-gassing packaging material such as
bubble foils, foams, etc. shall be avoided. Manufacturing
area shall be well ventilated.
For more detailed information please consult the
document
“Handling Instructions”
or contact Sensirion.
1.4 Reconditioning Procedure
As stated above extreme conditions or exposure to solvent
vapors may offset the sensor. The following reconditioning
procedure may bring the sensor back to calibration state:
Baking:
Re-Hydration:
100 – 105°C at < 5%RH for 10h
20 – 30°C at ~ 75%RH for 12h
9
.
100
60
40
20
0
-40
Max. Range
80
Normal
Range
-20
0
20
40
60
Temperature (°C)
80
100
120
Figure 4:
Operating Conditions
1.2 Sockets and Soldering
For maintain high accuracy specifications the sensor shall
not be soldered. Sockets may be used such as “Preci-dip /
Mill-Max 851-93-004-20-001” or similar.
Standard wave soldering ovens may be used at maximum
235°C for 20 seconds. For manual soldering contact time
must be limited to 5 seconds at up to 350°C
7
.
After wave soldering the devices should be stored at
>75%RH for at least 12h to allow the polymer to re-
hydrate.
In no case, neither after manual nor wave soldering, a
board wash shall be applied. In case of application with
exposure of the sensor to corrosive gases the soldering
pads of pins and PCB shall be sealed to prevent loose
contacts or short cuts.
1.3 Storage Conditions and Handling Instructions
It is of great importance to understand that a humidity
sensor is not a normal electronic component and needs to
be handled with care. Chemical vapors at high
concentration in combination with long exposure times
may offset the sensor reading.
For these reasons it is recommended to store the sensors
in original packaging including the sealed ESD bag at
following conditions: Temperature shall be in the range of
1.5 Temperature Effects
Relative humidity reading strongly depends on
temperature. Therefore, it is essential to keep humidity
sensors at the same temperature as the air of which the
relative humidity is to be measured. In case of testing or
qualification the reference sensor and test sensor must
show equal temperature to allow for comparing humidity
readings.
The packaging of SHT7x is designed for minimal heat
transfer from the pins to the sensor. Still, if the SHT7x
shares a PCB with electronic components that produce
heat it should be mounted in a way that prevents heat
transfer or keeps it as low as possible.
Furthermore, there are self-heating effects in case the
measurement frequency is too high. Please refer to
Section 3.3 for detailed information.
1.6 Light
The SHT7x is not light sensitive. Prolonged direct
exposure to sunshine or strong UV radiation may age the
housing.
8
9
7
235°C corresponds to 455°F, 350°C corresponds to 662°F
For example, please check www.sirel.ch
75%RH can conveniently be generated with saturated NaCl solution.
100 – 105°C correspond to 212 – 221°F, 20 – 30°C correspond to 68 – 86°F
Version 4.1 – July 2008
Datasheet SHT7x
1.7
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), PE, PEEK, PP, PB, PPS, PSU,
PVDF, PVF.
For sealing and gluing (use sparingly): High filled epoxy for
electronic packaging (e.g. glob top, underfill), and Silicone.
Out-gassing of these materials may also contaminate the
SHT7x (see Section 1.3). 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.
1.8 Wiring Considerations and Signal Integrity
SHT7x are often applied using wires. Carrying the SCK
and DATA signal parallel and in close proximity more than
10cm may result in cross talk and loss of communication.
This may be resolved by routing VDD and/or GND
between the two data signals and/or using shielded
cables. Furthermore, slowing down SCK frequency will
possibly improve signal integrity.
Please see the Application Note “ESD, Latchup and EMC”
for more information.
1.9 ESD (Electrostatic Discharge)
ESD immunity is qualified according to MIL STD 883E,
method 3015 (Human Body Model at
±2
kV).
Latch-up immunity is provided at a force current of
±100mA
with T
amb
= 80°C according to JEDEC78A. See
Application Note “ESD, Latchup and EMC” for more
information.
2.1 Power Pins (VDD, GND)
The supply voltage of SHT7x must be in the range of 2.4
and 5.5V, recommended supply voltage is 3.3V.
Decoupling of VDD and GND by a 100nF capacitor is
integrated on the backside of the sensor packaging.
The serial interface of the SHT7x is optimized for sensor
readout and effective power consumption. The sensor
cannot be addressed by I
2
C protocol, however, the sensor
can be connected to an I
2
C bus without interference with
other devices connected to the bus. Microcontroller must
switch between protocols.
VDD
R
P
SHT7x
(Slave)
B2G
71
1 2 3 4
Micro-
Controller
(Master)
DATA
SCK
2.4 – 5.5V
GND
VDD
Figure 5:
Typical application circuit, including pull up resistor R
P
.
2.2 Serial clock input (SCK)
SCK is used to synchronize the communication between
microcontroller and SHT7x. Since the interface consists of
fully static logic there is no minimum SCK frequency.
2.3 Serial data (DATA)
The DATA tri-state pin is used to transfer data in and out
of the sensor. For sending a command to the sensor,
DATA is valid on the rising edge of the serial clock (SCK)
and must remain stable while SCK is high. After the falling
edge of SCK DATA may be changed. For safe
communication DATA valid shall be extended T
SU
and T
HO
before the rising and after the falling edge of SCK,
respectively – see Figure 6. For reading data from the
sensor, DATA is valid T
V
after SCK has gone low and
remains valid until the next falling edge of SCK.
To avoid signal contention the microcontroller must only
drive DATA low. An external pull-up resistor (e.g. 10 k ) is
required to pull the signal high – it should be noted that
pull-up resistors may be included in I/O circuits of
microcontrollers. See Table 2 for detailed I/O characteristic
of the sensor.
2 Interface Specifications
Pin
1
2
3
4
Name
SCK
VDD
GND
DATA
Comment
Serial Clock, input only
Source Voltage
Ground
Serial Data, bidirectional
1 2 3 4
B2G
Table 1:
SHT7x pin assignment.
www.sensirion.com
71
Version 4.1 – July 2008
4/11
Datasheet SHT7x
2.4 Electrical Characteristics
The electrical characteristics such as power consumption,
low and high level, input and output voltages depend on
the supply voltage. Table 2 gives electrical characteristics
of SHT7x with the assumption of 5V supply voltage if not
stated otherwise. For proper communication with the
sensor it is essential to make sure that signal design is
strictly within the limits given in Table 3 and Figure 6.
Parameter
Conditions
min
Power supply DC
10
2.4
measuring
Supply current
average
11
2
sleep
Low level output
I
OL
< 4 mA
0
voltage
High level output
R
P
< 25 k
90%
voltage
Low level input
Negative going 0%
voltage
High level input
Positive going 80%
voltage
Input current on
pads
on
Output current
Tri-stated (off)
typ
3.3
0.55
28
0.3
max Units
5.5
V
1
mA
A
1.5
A
250
mV
Parameter
F
SCK
SCK Frequency
T
SCKx
SCK hi/low time
T
R
/T
F
SCK rise/fall time
T
FO
T
RO
T
V
T
SU
T
HO
*
**
***
****
Conditions
VDD > 4.5V
VDD < 4.5V
min
0
0
100
1
typ max Units
0.1
0.1
200
10
40
**
5
1
*
20
200
**
***
***
****
MHz
MHz
ns
ns
ns
ns
ns
ns
ns
ns
DATA fall time
DATA rise time
DATA valid time
DATA setup time
DATA hold time
OL = 5pF
OL = 100pF
3.5
30
**
200 250
100 150
10
15
T
R_max
+ T
F_max
= (F
SCK
)
-1
– T
SCKH
– T
SCKL
T
R0
is determined by the R
P
*C
bus
time-constant at DATA line
T
V_max
and T
SU_max
depend on external pull-up resistor (R
P
) and total bus
line capacitance (Cbus) at DATA line
T
H0_max
< T
V
– max (T
R0
, T
F0
)
100% VDD
20% VDD
100% VDD
1
4
20
A
mA
A
Table 3:
SHT7x I/O signal characteristics, OL stands for Output
Load, entities are displayed in Figure 6.
3 Communication with Sensor
3.1 Start up Sensor
As a first step the sensor is powered up to chosen supply
voltage VDD. The slew rate during power up shall not fall
below 1V/ms. After power-up the sensor needs 11ms to
get to Sleep State. No commands must be sent before
that time.
3.2 Sending a Command
To initiate a transmission, a Transmission Start sequence
has to be issued. It consists of a lowering of the DATA line
while SCK is high, followed by a low pulse on SCK and
raising DATA again while SCK is still high – see Figure 7.
10
Table 2:
SHT7x DC characteristics. R
P
stands for pull up
resistor, while I
OL
is low level output current.
T
SCK
T
SCKH
T
SCKL
T
R
T
F
90%
10%
T
SU
DATA valid write
T
HO
DATA valid read
T
V
T
RO
T
FO
90%
10%
SCK
DATA
SCK
90%
10%
Figure 6:
Timing Diagram, abbreviations are explained in
Table 3. Bold DATA line is controlled by the sensor, plain DATA
line is controlled by the micro-controller. Both valid times refer to
the left SCK toggle.
DATA
Figure 7:
"Transmission Start" sequence
90%
10%
10
Recommended voltage supply for highest accuracy is 3.3V, due to sensor
calibration.
11
Minimum value with one measurement of 8 bit accuracy without OTP reload
per second, typical value with one measurement of 12bit accuracy per
second.
The subsequent command consists of three address bits
(only ‘000’ is supported) and five command bits. The
SHT7x indicates the proper reception of a command by
pulling the DATA pin low (ACK bit) after the falling edge of
the 8th SCK clock. The DATA line is released (and goes
high) after the falling edge of the 9th SCK clock.
5/11
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Version 4.1 – July 2008
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