SHTC1 datasheet(6/14 Pages) ETC2

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Version 3 – May 2014

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4 Interface Specifications

The SHTC1 supports I2C fast mode (SCL clock frequency

from 0 to 400 kHz) with clock stretching. For detailed

information on the I2C protocol, refer to NXP I2C-bus

specification and user manual UM10204, Rev. 4,

February 13, 2012:

http://ics.nxp.com/support/documents/interface/pdf/I2C.bu

s.specification.pdf

The SHTC1 comes in a 4-pin package – see Table 7.

Pin Name

Comments

VDD Supply voltage

SCL Serial clock, bidirectional

SDA Serial data, bidirectional

VSS Ground

Table 7 SHTC1 pin assignment (top view). The center pad is

internally connected to VSS.

Power-supply pins supply voltage (VDD) and ground

(VSS) must be decoupled with a 100 nF capacitor that

shall be placed as close to the sensor as possible – see

Figure 6.

SCL is used to synchronize the communication between

microcontroller and the sensor. The master must keep the

clock frequency within 0 to 400 kHz as specified in Table

6. The SHTC1 may pull down the SCL line when clock

stretching is enabled.

The SDA pin is used to transfer data in and out of the

sensor. For safe communication, the timing specifications

defined in the I2C manual must be met.

To avoid signal contention, the microcontroller must only

drive SDA and SCL low. External pull-up resistors (e.g.

10 kΩ) are required to pull the signal high. For

dimensioning resistor sizes please take bus capacity

requirements into account. It should be noted that pull-up

resistors may be included in I/O circuits of

microcontrollers.

Figure 6 Typical application circuit, including pull-up resistors

RP and decoupling of VDD and VSS by a capacitor.

For good performance of the SHTC1 in the application, it

is important to know that the center pad of the SHTC1

offers the best thermal contact to the temperature sensor.

For more information on design-in, please refer to the

document “SHTxx Design Guide”.

For mechanical reasons the center pad should be

soldered. Electrically, the center pad is internally

connected to GND and may be connected to the GND net

on the PCB or left floating.

5 Operation and Communication

All commands and memory locations of the SHTC1 are

mapped to a 16-bit address space which can be accessed

via the I2C protocol.

SHTC1

Bin.

Dec.

Hex.

I2C address

111’0000

112

0x70

Table 8 SHTC1

I2C device address.

5.1 Power-Up and Communication Start

Upon VDD reaching the power-up voltage level VPOR, the

SHTC1 enters idle state after a duration of tPU. In idle

state, the SHTC1 is ready to receive commands from the

master (microcontroller).

Each transmission sequence begins with START condition

(S) and ends with an (optional) 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.

Please note that in case VDD is set to 0 V (GND), e.g. in

case of a power off of the SHTC1, the SCL and SDA pads

are also pulled to GND. Consequently, the I2C bus is

blocked while VDD of the SHTC1 is set to 0 V.

5.2 Measurement Commands

The SHTC1 provides the possibility to define the sensor

behavior during measurement as well as the transmission

sequence of measurement results. These characteristics

are defined by the appropriate measurement command

(see Table 9). Each measurement command triggers both

a temperature and a humidity measurement.

Clock Stretching

Enabled

Clock Stretching

Disabled

Read T

First

Read H

First

Read T

First

Read H

First

0x7CA2

0x5C24

0x7866

0x58E0

Table 9 Measurement commands.

SHTC1

AXY89

SDA

SCL

GND

VDD

MCU (master)

SCL OUT

SDA OUT

SDA IN

SCL IN

SHTC1

(slave)

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