SHT3X-DIS datasheet(7/18 Pages) ETC2

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Datasheet SHT3x-DIS

www.sensirion.com

October 2015 - Version 1

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The LSB switches between read or write header. The

wiring for the default address is shown in Table 7 and

Figure 8. 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 VSS

I2C address B

0x45

ADDR (pin 2)

connected to VDD

Table 7 I2C device address

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 350 ns 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 connect to VDD.

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 specification12.

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

http://www.nxp.com/documents/user_manual/UM10204.pdf

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 VPOR specified in Table 3.

After reaching this threshold voltage the sensor needs

the time tPU 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. The stop

condition is optional. 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 8.

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.

In single shot mode different measurement commands

can be selected. The 16 bit commands are shown in

Table 8. They differ with respect to repeatability (low,

medium and high) and clock stretching (enabled or

disabled).

The repeatability setting influences the measurement

duration and thus the overall energy consumption of the

sensor. This is explained in section 0.

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