Datasheet SHT21

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Version 5 – October 2022

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3 Interface Specifications

Pin Name

Comment

1

SDA Serial Data, bidirectional

2

VSS Ground

5

VDD Supply Voltage

6

SCL Serial Clock, bidirectional

3,4

NC Not Connected

Table 2 SHT2x pin assignment, NC remain floating (top view)

3.1

Power Pins (VDD, VSS)

The supply voltage of SHT2x must be in the range of 2.1 –

3.6 V, recommended supply voltage is 3.0 V. 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 11.

3.2

Serial clock (SCL)

SCL is used to synchronize the communication between

microcontroller (MCU) and the sensor. Since the interface

consists of fully static logic there is no minimum SCL

frequency.

3.3

Serial SDA (SDA)

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

sensor. For sending a command to the sensor, SDA is

valid on the rising edge of SCL and must remain stable

while SCL is high. After the falling edge of SCL the SDA

value may be changed. For safe communication SDA shall

be valid tSU and tHD before the rising and after the falling

edge of SCL, respectively – see Figure 12. For reading

data from the sensor, SDA is valid tVD after SCL has gone

low and remains valid until the next falling edge of SCL.

Figure 11 Typical application circuit, including pull-up resistors

RP and decoupling of VDD and VSS by a capacitor.

To avoid signal contention the micro-controller unit (MCU)

must only drive SDA and SCL low. External pull-up

resistors (e.g. 10 kΩ), are required to pull the signal high.

For the choice of resistor size please take bus capacity

requirements into account (compare Table 5). It should be

noted that pull-up resistors may be included in I/O circuits

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 I/O 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 JEDEC JESD22-

A114 method (Human Body Model at

4kV), JEDEC

JESD22-A115 method (Machine Model

200V) and ESDA

ESD-STM5.3.1-1999 and AEC-Q100-011 (Charged

Device Model, 750 V corner pins, 500 V other pins). Latch-

up immunity is provided at a force current of

100 mA with

Tamb = 125°C according to JEDEC JESD78. For exposure

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 12.

Parameter

Conditions

min

typ

max Units

Output Low

Voltage, VOL

VDD = 3.0 V,

-4 mA < IOL < 0mA

0

-

0.4

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.

SDA

SCL

GND

VDD

MCU (master)

RP

RP

SCL OUT

SDA OUT

SDA IN

SCL IN

SHT2x

(slave)

1

6

5

2

4

3