Data Sheet

Datasheet SHT3x-DIS
www.sensirion.com May 2018- Version 5 9/22
The dynamical switching requires individual ADDR lines
to the sensors.
Please note that the I2C address is represented through
the 7 MSBs of the I2C read or write header. The LSB
switches between read or write header. The wiring for
the default address is shown in Table 8 and Figure 11.
The ADDR pin must not be left floating. Please note that
only the 7 MSBs of the I2C Read/Write header constitute
the I2C Address.
SHT3x-DIS
I2C Address in Hex.
representation
Condition
I2C address A
0x44 (default)
ADDR (pin 2)
connected to logic
low
I2C address B
0x45
ADDR (pin 2)
connected to logic
high
Table 8 I2C device addresses.
3.5 ALERT Pin
The alert pin may be used to connect to the interrupt pin
of a microcontroller. The output of the pin depends on
the value of the RH/T reading relative to programmable
limits. Its function is explained in a separate application
note. If not used, this pin must be left floating. The pin
switches high, when alert conditions are met. The
maximum driving loads are listed in Table 3. Be aware
that self-heating might occur, depending on the amount
of current that flows. Self-heating can be prevented if the
Alert Pin is only used to switch a transistor.
3.6 nRESET Pin
The nReset pin may be used to generate a reset of the
sensor. A minimum pulse duration of 1 µs is required to
reliably trigger a reset of the sensor. Its function is
explained in more detail in section 4. If not used it is
recommended to leave the pin floating or to connect it to
VDD with a series resistor of R ≥2 kΩ. However, the
nRESET pin is internally connected to VDD with a pull
up resistor of R = 50 kΩ (typ.).
4 Operation and Communication
The SHT3x-DIS supports I2C fast mode (and
frequencies up to 1000 kHz). Clock stretching can be
enabled and disabled through the appropriate user
command. For detailed information on the I2C protocol,
refer to NXP I2C-bus specification
12
.
12
http://www.nxp.com/documents/user_manual/UM10204.pdf
After sending a command to the sensor a minimal
waiting time of 1ms is needed before another command
can be received by the sensor.
All SHT3x-DIS commands and data are mapped to a 16-
bit address space. Additionally, data and commands are
protected with a CRC checksum. This increases
communication reliability. The 16 bits commands to the
sensor already include a 3 bit CRC checksum. Data sent
from and received by the sensor is always succeeded by
an 8 bit CRC.
In write direction it is mandatory to transmit the
checksum, since the SHT3x-DIS only accepts data if it is
followed by the correct checksum. In read direction it is
left to the master to read and process the checksum.
4.1 Power-Up and Communication Start
The sensor starts powering-up after reaching the power-
up threshold voltage V
POR
specified in Table 3. After
reaching this threshold voltage the sensor needs the
time t
PU
to enter idle state. Once the idle state is entered
it is ready to receive commands from the master
(microcontroller).
Each transmission sequence begins with a START
condition (S) and ends with a STOP condition (P) as
described in the I2C-bus specification. Whenever the
sensor is powered up, but not performing a
measurement or communicating, it automatically enters
idle state for energy saving. This idle state cannot be
controlled by the user.
4.2 Starting a Measurement
A measurement communication sequence consists of a
START condition, the I2C write header (7-bit I2C device
address plus 0 as the write bit) and a 16-bit
measurement command. The proper reception of each
byte is indicated by the sensor. It pulls the SDA pin low
(ACK bit) after the falling edge of the 8th SCL clock to
indicate the reception. A complete measurement cycle is
depicted in Table 9.
With the acknowledgement of the measurement
command, the SHT3x-DIS starts measuring humidity
and temperature.
4.3 Measurement Commands for Single Shot
Data Acquisition Mode
In this mode one issued measurement command
triggers the acquisition of one data pair. Each data pair
consists of one 16 bit temperature and one 16 bit
humidity value (in this order). During transmission each
data value is always followed by a CRC checksum, see
section 4.4.