Datasheet SHT7x
www.sensirion.com Version 5 – December 2011 4/12
1.6 Light
The SHT7x is not light sensitive. Prolonged direct
exposure to sunshine or strong UV radiation may age the
housing.
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): Use 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, Latch-up 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, Latch-up and EMC” for more
information.
2 Interface Specifications
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 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.
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 the DATA value 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 kΩ) is
required to pull the signal high – it should be noted that
pull-up resistors may be included in I/O circuits of
VDD
GND
DATA
SCK
B2G
Micro-
Controller
(Master)
SHT7x
(Slave)
B2G
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