SHT1x / SHT7x Relative Humidity & Temperature Sensor System

www.sensirion.com

v2.02 July 2004

4/9

Command

wait for data ready

MSB

LSB

Checksum

0

0

0

0

Figure 6 Overview of Measurement Sequence (TS = Transmission Start)

2.3 Status Register

Some of the advanced functions of the SHTxx are available

through the status register. The following section gives a

brief overview of these features. A more detailed description

is available in the application note “Status Register”

Command

Status

Reg

00

0

11

0

0

0

Figure 7 Status Register Write

Command

Status

Reg

Checksum

0011

0

0

0

1

Figure 8 Status Register Read

Bit Type

Description

Default

7

reserved

0

6

R

End of Battery (low voltage detection)

‘0’ for Vdd > 2.47

‘1’ for Vdd < 2.47

X No default value,

bit

is

only

updated after a

measurement

5

reserved

0

4

reserved

0

3

For Testing only, do not use

0

2

R/W

Heater

0

off

1

R/W

no reload from OTP

0

reload

0

R/W

’1’ = 8bit RH / 12bit Temperature resolution

’0’ = 12bit RH / 14bit Temperature resolution

0

12bit RH

14bit Temp.

Table 3

Status Register Bits

2.3.1 Measurement resolution

The default measurement resolution of 14bit (temperature)

and 12bit (humidity) can be reduced to 12 and 8bit. This is

especially useful in high speed or extreme low power

applications.

2.3.2 End of Battery

The “End of Battery” function detects VDD voltages below

2.47 V. Accuracy is

±0.05 V

2.3.3 Heater

An on chip heating element can be switched on. It will

increase the temperature of the sensor by 5-15 °C (9-27 °F).

Power consumption will increase by ~8 mA @ 5 V.

Applications:

By comparing temperature and humidity values before and

after switching on the heater, proper functionality of both

sensors can be verified.

• In high (>95 %RH) RH environments heating the sensor

element will prevent condensation, improve response

time and accuracy

Warning: While heated the SHTxx will show higher

temperatures and a lower relative humidity than with no

heating.

VDD=5V, Temperature = 25 °C unless otherwise noted

Parameter

Conditions

Min. Typ. Max. Units

Power supply DC

2.4

5

5.5 V

measuring

550

µA

Supply current

average

µA

sleep

0.3

1

µA

Low level output voltage

0

20% Vdd

High level output voltage

75%

100% Vdd

Low level input voltage Negative going

0

20% Vdd

High level input voltage Positive going 80%

100% Vdd

Input current on pads

1

µA

Output peak current

on

4

mA

Tristated (off)

10

µA

Table 4

SHTxx DC Characteristics

Parameter

Conditions

Min Typ. Max. Unit

VDD > 4.5 V

10 MHz

VDD < 4.5 V

1 MHz

Output load 5 pF

3.5 10

20 ns

Output load 100 pF 30 40 200 ns

100

ns

DATA valid time

250

ns

DATA set up time

100

ns

DATA hold time

0

10

ns

200

ns

Table 5

SHTxx I/O Signals Characteristics

SCK

DATA

Figure 9 Timing Diagram

1)

Parameters are periodically sampled and not 100% tested

(2)

With one measurement of 8 bit accuracy without OTP reload per second

(3)

With one measurement of 12bit accuracy per second