SHT3X-DIS datasheet(6/18 Pages) ETC2

6 / 18 page

Datasheet SHT3x-DIS

www.sensirion.com

October 2015 - Version 1

6/18

Pin Assignment

The SHT3x-DIS comes in a tiny 8-pin DFN package –

see Table 6.

Name

Comments

SDA

Serial data; input / output

ADDR

Address pin; input; connect to either

VDD or VSS, do not leave floating

ALERT

Indicates alarm condition; output; must

be left floating if unused

SCL

Serial clock; input / output

VDD

Supply voltage; input

nRESET

Reset pin active low; input; if not used it

is recommended to connect to VDD

No electrical function; to be connected to

VSS

Ground

Table 6 SHT3x-DIS pin assignment (transparent top view).

Dashed lines are only visible if viewed from below. The die

pad is internally connected to VSS.

3.1

Power Pins (VDD, VSS)

The electrical specifications of the SHT3x-DIS are

shown in Table 3. The power supply pins must be

decoupled with a 100 nF capacitor that shall be placed

as close to the sensor as possible – see Figure 8 for a

typical application circuit.

3.2

Serial Clock and Serial Data (SCL, SDA)

SCL is used to synchronize the communication

between microcontroller and the sensor. The clock

frequency can be freely chosen between 0 to 1000 kHz.

Commands with clock stretching according to I2C

Standard11 are supported.

The SDA pin is used to transfer data to and from the

sensor. Communication with frequencies up to 400 kHz

must meet the I2C Fast Mode11 standard.

Communication frequencies up to 1 Mhz are supported

following the specifications given in Table 20.

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

Both SCL and SDA lines are open-drain I/Os with

diodes to VDD and VSS. They should be connected to

external pull-up resistors (please refer to Figure 8). A

device on the I2C bus must only drive a line to ground.

The external pull-up resistors (e.g. Rp=10 kΩ) are

required to pull the signal high. For dimensioning

resistor sizes please take bus capacity and

communication frequency into account (see for

example Section 7.1 of NXPs I2C Manual for more

details11). It should be noted that pull-up resistors may

be included in I/O circuits of microcontrollers. It is

recommended to wire the sensor according to the

application circuit as shown in Figure 8.

Figure 8 Typical application circuit. Please note that the

positioning of the pins does not reflect the position on the

real sensor. This is shown in Table 6.

3.3

Die Pad (center pad)

The die pad or center pad is visible from below and

located in the center of the package. It is electrically

connected to VSS. Hence electrical considerations do

not impose constraints on the wiring of the die pad.

However, due to mechanical reasons it is

recommended to solder the center pad to the PCB. For

more information on design-in, please refer to the

document “SHTxx Design Guide”.

3.4

ADDR Pin

Through the appropriate wiring of the ADDR pin the I2C

address can be selected (see Table 7 for the respective

addresses). Aside from hard wiring the ADDR pin to

VDD or VSS, it is also possible to use it as a selector

pin. This means that the address of the sensor can be

changed dynamically during operation by switching the

level on the ADDR pin. The only constraint is that the

level has to stay constant starting from the I2C start

condition until the communication is finished. This

allows to connect more than two SHT3x-DIS onto the

same bus. 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.

ADDR(2)

ALERT(3)

die

pad

R(7)

SDA(1)

SCL(4)

VDD(5)

VSS(8)

nRESET(6)

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