Datasheet SHT21

www.sensirion.com

Version 1.0 – January 2010

6/12

of MCUs.

See Table 4 and Table 5 for detailed I/O

characteristic of the sensor.

4 Electrical Characteristics

4.1

Absolute Maximum Ratings

The electrical characteristics of SHT2x are defined in

Table 1. The absolute maximum ratings as given in Table

3 are stress ratings only and give additional information.

Functional operation of the device at these conditions is

not implied. Exposure to absolute maximum rating

conditions for extended periods may affect the sensor

reliability (e.g. hot carrier degradation, oxide breakdown).

Parameter

min

max

Units

VDD to VSS

-0.3

5

V

Digital IO Pins (SDA, SCL)

to VSS

-0.3

VDD + 0.3

V

Input Current on any Pin

-100

100

mA

Table 3 Electrical absolute maximum ratings

ESD immunity is qualified according to MIL STD 883E,

method 3015 (Human Body Model at 2 kV). Latch-up

immunity is provided at a force current of 100mA with

beyond named limits the sensor needs additional

protection circuit.

4.2

Input / Output Characteristics

The electrical characteristics such as power consumption,

low and high level input and output voltages depend on

the supply voltage. For proper communication with the

sensor it is essential to make sure that signal design is

strictly within the limits given in Table 4 & 5 and Figure 10.

Parameter

Conditions

min

typ

max

Units

Output Low

Voltage, VOL

VDD = 3.0 V,

-4 mA < IOL < 0mA

0

-

0.4

V

Output High

Voltage, VOH

70%

VDD

-

VDD

V

Output Sink

Current, IOL

-

-

-4

mA

Input Low

Voltage, VIL

0

-

30%

VDD

V

Input High

Voltage, VIH

70%

VDD

-

VDD

V

Input Current

VDD = 3.6 V,

VIN = 0 V to 3.6 V

-

-

±1

uA

Table 4 DC characteristics of digital input/output pads. VDD =

2.1 V to 3.6 V, T = -40 °C to 125 °C, unless otherwise noted.

Figure 10

Timing Diagram for Digital Input/Output Pads,

abbreviations are explained in Table 5. SDA directions are seen

from the sensor. Bold SDA line is controlled by the sensor, plain

SDA line is controlled by the micro-controller. Both valid times

(SDA read and SDA write) refer to the left SCL toggle.

Parameter

min

typ

max

Units

0

-

0.4

MHz

0.6

-

-

µs

1.3

-

-

µs

100

-

-

ns

0

-

900

ns

0

-

400

ns

0

-

100

ns

0

-

300

ns

0

-

400

pF

fast mode. Entities are displayed in Figure 10. VDD = 2.1V to

3.6V, T = -40°C to 125°C, unless otherwise noted.

5 Communication with Sensor

Sections please refer to the following website:

Furthermore, please note, that Sensirion provides a

sample

code

on

its

home

page

–

compare

5.1

Start Up Sensor

As a first step, the sensor is powered up to the chosen

supply voltage VDD (between 2.1 V and 3.6 V). After

power-up, the sensor needs at most 15 ms, while SCL is

high, for reaching idle state, i.e. to be ready accepting

SCL

70%

30%

SDA

70%

30%

SDA valid read

DATA IN

SDA

70%

30%

DATA OUT

SDA valid write