Datasheet SHT7x
www.sensirion.com
Version 4.1 – July 2008
4/11
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 Tamb = 80°C according to JEDEC78A. See
Application Note “ESD, Latchup and EMC” for more
information.
2 Interface Specifications
Pin
Name
Comment
1
SCK
Serial Clock, input only
2
VDD
Source Voltage
3
GND
Ground
4
DATA
Serial Data, bidirectional
Table 1: SHT7x pin assignment.
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 I2C protocol, however, the sensor
can be connected to an I2C bus without interference with
other devices connected to the bus. Microcontroller must
switch between protocols.
Figure 5: Typical application circuit, including pull up resistor RP.
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 TSU and THO
before the rising and after the falling edge of SCK,
respectively – see Figure 6. For reading data from the
sensor, DATA is valid TV 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.
2.4 – 5.5V
GND
VDD
DATA
SCK
71
B2G
1 2 3 4
Micro-
Controller
(Master)
SHT7x
(Slave)
VDD
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