SCD4x
Breaking the size barrier in optical CO2 sensing

Features▪ Photoacoustic NDIR sensor technology PASens®
▪ Small form factor: 10.1 x 10.1 x 6.5 mm3▪ Reflow solderable for cost-effective assembly▪ Digital I2C interface▪ Integrated temperature and humidity sensor

Product Variants▪ SCD40: Base accuracy, specified measurement
range 400 –2’000 ppm▪ SCD41: High accuracy, specified measurement
range 400 – 5’000 ppm, compatible with
California Title 241, RESET® 2 and WELL BuildingStandard™ 3, features single shot operation mode

Product Summary
The SCD4x is Sensirion’s second generation optical CO2
sensor. This sensor builds on the photoacoustic NDIR
sensing principle and Sensirion’s patented PASens® andCMOSens® technology to offer high accuracy at an
attractive price and small form factor. SMD assembly
allows cost- and space-effective integration of the sensor
combined with maximal freedom of design. On-chipsignal compensation is realized with the built-in SHT4xhumidity and temperature sensor.

CO2 is a key indicator for indoor air quality (IAQ), as highlevels compromise human cognitive performance andwell-being. The SCD4x enables smart ventilation
regulation to help improve energy efficiency and humancomfort. Moreover, indoor air quality monitors and otherconnected devices based on the SCD4x can help
maintain low CO2 concentrations for a healthy, productive
environment.

Functional Block Diagram

Product Overview
Products
Details
SCD40-D-R2 Base accuracy, specified range
400 – 2’000 ppm
SCD41-D-R2 High accuracy, specified range
400 – 5’000 ppm, compatible with
common IAQ/building standards,
single shot operation feature123

1 2022 California Building Energy Efficiency Standards for Residential and Nonresidential Buildings
2 RESET Air Standard v2.0 Grade B
3 WELL v2 pilot, Q4 2022

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Table of Contents
1

Sensor Performance ......................................................................................................................................... 3
1.1
CO2 Sensing Performance .......................................................................................................................... 3
1.2
Humidity Sensing Performance ................................................................................................................... 3
1.3
Temperature Sensing Performance............................................................................................................. 3
2 Specifications .................................................................................................................................................... 4
2.1
Electrical Specifications ............................................................................................................................... 4
2.2
Absolute Maximum Ratings ......................................................................................................................... 4
2.3
Interface Specifications ............................................................................................................................... 5
2.4
Timing Specifications................................................................................................................................... 6
2.5
Material Contents ........................................................................................................................................ 6
3 Digital Interface Description ............................................................................................................................. 7
3.1
Power-Up and Communication Start ........................................................................................................... 7
3.2
Sensor I2C Address ..................................................................................................................................... 7
3.3
Data Type & Length .................................................................................................................................... 7
3.4
Command Sequence Types ........................................................................................................................ 7
3.5
SCD4x Command Overview ........................................................................................................................ 8
3.6
Basic Commands ........................................................................................................................................ 9
3.7
On-Chip Output Signal Compensation ...................................................................................................... 10
3.8
Field Calibration ........................................................................................................................................ 13
3.9
Low Power Periodic Measurement Mode .................................................................................................. 15
3.10 Advanced Features ................................................................................................................................... 16
3.11 Single Shot Measurement Mode (SCD41 Only) ........................................................................................ 19
3.12 Checksum Calculation ............................................................................................................................... 23
4 Mechanical Specifications .............................................................................................................................. 24
4.1
Package Outline ........................................................................................................................................ 24
4.2
Land Pattern Recommendation ................................................................................................................. 24
4.3
Tape & Reel Package................................................................................................................................ 25
4.4
Moisture Sensitivity Level .......................................................................................................................... 25
4.5
Soldering Instructions ................................................................................................................................ 26
4.6
Traceability and Identification .................................................................................................................... 26
5 Ordering Information....................................................................................................................................... 27
5.1
Historical Information ................................................................................................................................. 27
6 Revision History .............................................................................................................................................. 28

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1

Sensor Performance

1.1 CO2 Sensing Performance
Default conditions of 25 °C, 50 %RH, ambient pressure of 1013 mbar, continuous operation in periodic measurement mode(see Section 3.6.1) and 3.3 V supply voltage apply to values in the table below, unless otherwise stated.
Parameter
CO2 output range4
SCD40 CO2 measurement accuracy5
SCD41 CO2 measurement accuracy5
Repeatability
Response time6
Additional accuracy drift per year, starting
after five years7

Conditions
400 ppm – 2’000 ppm
400 ppm – 1’000 ppm
1’001 ppm – 2’000 ppm
2’001 ppm – 5’000 ppm
Typicalτ63%, typical, step change 400 – 2’000 ppm
Typical, same CO2 concentration range as
sensor’s specified measurement accuracyValue
0 – 40’000 ppm±(50 ppm + 5% of reading)±(50 ppm + 2.5% of reading)±(50 ppm + 3% of reading)±(40 ppm + 5% of reading)±10 ppm
60 s±(5 ppm + 0.5 % of reading)

Table 1: SCD40 and SCD41 CO2 sensor specifications

1.2 Humidity Sensing Performance
SCD4x design-in, self-heating, operation mode and the surrounding environment affects RH/T sensor performance. To achieve thespecifications in Table 2, the temperature-offset of the SCD4x inside the customer device must be set correctly (see Section 3.7).
Parameter
Humidity measurement range
Accuracy (typ.)Repeatability
Response time6
Accuracy drift

Conditions
15 °C – 35 °C, 20 %RH – 65 %RH-10 °C – 60 °C, 0 %RH – 100 %RH
Typicalτ63%, typical, periodic measurement mode-

Value
0 %RH – 100 %RH±6 %RH±9 %RH±0.4 %RH
90 s<0.25 %RH / year

Table 2: SCD4x humidity sensor specifications

1.3 Temperature Sensing Performance
SCD4x design-in, self-heating, operation mode and the surrounding environment affects RH/T sensor performance. To achieve thespecifications in Table 3, the temperature-offset of the SCD4x inside the customer device must be set correctly (see Section 3.7)
Parameter
Temperature measurement range
Accuracy (typ.)Repeatability
Response time6
Accuracy drift

Conditions
15 °C – 35 °C-10 °C – 60 °C
τ63%, typical, periodic measurement mode-Value
- 10 °C – 60 °C± 0.8 °C
± 1.5 °C
± 0.1 °C
120 s
< 0.03 °C / year

Table 3: SCD4x temperature sensor specifications

4 Exposure to CO2 concentrations smaller than 400 ppm can affect the accuracy of the sensor with ASC enabled.

5 Deviation from a high-precision reference with gas mixtures having a ±2% tolerance. Rough handling, shipping, sensor assembly and long-term drift can impact sensor

accuracy. Accuracy can be restored by performing forced recalibration (FRC) no less than 5 days after sensor assembly, or maintained by sensor operation with automatic
self-calibration (ASC) enabled using default parameters and weekly exposure to air with CO2 concentrations at 400 ppm. See Section 3.8 for details.
6 Response time depends on design-in, signal update rate and environment of the sensor in the final application.
7 Deviation is additional to standard accuracy specifications and obtained either after performing FRC or in continuous sensor operation with ASC enabled using default
parameters and weekly exposure to air with CO2 concentrations at 400 ppm. Maximum additional accuracy drift per year starting after five years estimated from stress tests is±(5 ppm + 2% of reading). Stronger drift may occur if the sensor is not handled according to its handling instructions.

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2

Specifications

2.1 Electrical Specifications
Parameter
Supply voltage DC8
Unloaded supply voltage ripple (peak to peak)9Symbol
VDD
VRPP

Peak supply current10

Ipeak

Average supply current for periodic measurementmode (1 measurement every 5 seconds)

IDD

Average supply current for low power periodic
measurement mode (1 measurement every 30
seconds)

IDD

Average supply current for single shot mode, 1
measurement every 5 minutes (SCD41 only)11

IDD

Input high level voltage
Input low level voltage
Output low level voltage

VIH
VIL
VOL

Conditions

Min.
2.4

Typical
3.3 or 5.0

VDD = 3.3 V
VDD = 5 V
VDD = 3.3 V
VDD = 5 V
VDD = 3.3 V
VDD = 5 V

175
115
15
11
3.2
2.8

VDD = 3.3 V
VDD = 5 V

0.45
0.36
0.65 x VDD

3 mA sink current

Max.
5.5
30
205
137
18
13
3.5
3

Units
V
mV
mA
mA
mA
mA
mA

0.5
0.4
1 x VDD
0.3 x VDD
0.66

mA
mA
V

mA

Table 4: SCD4x electrical specifications

2.2 Absolute Maximum Ratings
Stress levels beyond those listed in Table 5 may cause permanent damage to the device. Exposure to minimum/maximum
rating conditions for extended periods may affect sensor performance and device reliability.
Parameter
Temperature operating conditions
Humidity operating conditions12
MSL Level
DC supply voltage
Max. voltage on pins SDA, SCL, GND
Input current on pins SDA, SCL, GND
Short term storage temperature13
Recommended storage temperature
ESD HBM (pads and metal cap)
ESD CDM
Maintenance interval
Sensor lifetime15

Conditions
Non-condensing

Maintenance free when the ASC
algorithm14 is used.
Typical operating conditions

Value-10 – 60 °C
0 – 95 %RH
1-0.3 V – 6.0 V-0.3 V – VDD + 0.3 V-280 mA – 100 mA-40 °C – 70 °C
10 °C – 50 °C
2 kV
500 V
None
>10 years

Table 5: SCD4x operation conditions, lifetime and maximum ratings

8 Supply voltage must be kept constant for stable sensor operation.
9 Determined on the supply voltage without the load of the sensor.
10 Refers to sustained current.

11 On-demand measurement with adjustable interval. See Section 3.11 for details.
12 Accuracy can be reduced at relative humidity levels lower than 10%.

13 Short term storage refers to temporary conditions e.g., during transport.
14 For proper function of the ASC field-calibration algorithm with default parameters, SCD4x must be exposed to air with CO2 concentrations at 400 ppm on a weekly basis.
15 Sensor tested over simulated lifetime of >10 years for an indoor environment mission profile.

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2.3 Interface Specifications
The SCD4x comes in an LGA package (Table 6). Further details on the sensor’s package can be found in Section 4.1. A
recommended land pattern for SCD4x can be found in Section 4.2.
Name

Comments

VDD

Supply voltage

VDDH

Supply voltage IR source, must
be connected to VDD on
customer PCB

GND

Ground contact

SDA

I2C serial data, bidirectional

SCL

I2C serial clock

DNC

Do not connect, pads must be
soldered to a floating pad on
the customer PCB

Table 6: Pin assignment (top view). The notched corner of the protection membrane serves as a polarity mark to indicate pin 1 location.

VDD and VDDH are used to supply the sensor and must always be kept at the same voltage, i.e. both should be connected tothe same power supply. The combined maximum current drawn on VDD and VDDH is indicated in Table 4. VDD and VDDH
must be connected to each other close to the sensor on the customer PCB.
For sensor operation, a low noise power supply, such as a low-dropout regulator (LDO), which can handle the peak supply
current as specified in Table 4 must be chosen. Due to the sensor’s internal regulation, higher transient currents (on thetimescale of microseconds) may be observed. These transient currents can be neglected in typical design-in scenarios due tothe parasitic R/L/C of the leads as well as the load regulation characteristics of the supply. Additionally, to avoid interferencewith the sensor regulation, the supply voltage without the load of the sensor must not vary by more than 30 mV (e.g. ripples ordrops caused by other loads). Operating the sensor with a separate LDO is recommended.
SCD4x uses I2C communication based on NXP’s I2C-bus specification and user manual16. I2C standard and fast mode operation
are supported. SCL is used to synchronize the I2C communication between the master (microcontroller) and the slave (sensor).
The SDA pin is used to transfer data to and from the sensor. For safe communication, the timing specifications defined in the
I2C manual16 and Section 2.4 must be met. Both SCL and SDA lines should be connected to external pull-up resistors(e.g. Rp = 10 kΩ, see Figure 1). To avoid signal contention, the microcontroller must only drive SDA and SCL low. For
dimensioning resistor sizes, please take bus capacity and communication frequency into account (see example in Section 7.1
of NXPs I2C Manual for more details16). Note that pull-up resistors may be included in the I/O circuits of microcontrollers.

Figure 1: Typical application circuit (representative and not to scale).

16 NXP I2C-bus specification and user manual UM10204, Rev.6, 4 April 2014www.sensirion.com

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2.4 Timing Specifications
Table 7 lists the timings of the SCD4x17.
Parameter

Condition

Min.

Max.

Unit

Power-up time

After hard reset, VDD ≥ 2.25 V

-

30

ms

Soft reset time

After re-initialization (i.e. reinit)

-

30

ms

SCL clock frequency

-

0

400

kHz

Table 7: System timing specifications.

2.5 Material Contents
The device is fully REACH and RoHS compliant.

17 Timing specifications based on the NXP I2C-bus specification and user manual UM10204, Rev.6, 4 April 2014www.sensirion.com

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3

Digital Interface Description

3.1 Power-Up and Communication Start
The sensor starts powering-up after reaching the power-up threshold voltage VDD,min and will take up to the maximum of thepower-up time to enter the idle state. Once the idle state has been reached, it is ready to receive commands from the master.
Each transmission sequence begins with a START condition (S) and ends with a STOP condition (P) as described in the I 2Cbus specification.

3.2 Sensor I2C Address
SCD4x can be addressed by sending its 7-bit I2C address, given in Table 8, followed by an eighth bit denoting the communication
direction: a “zero” indicates a “write” request, a “one” a “read” request.
SCD4x

Hex. CodeI2C address

0x62

Table 8: I2C device address

3.3 Data Type & Length
Data sent to and received from the sensor consists of a sequence of 16-bit commands and/or 16-bit words (each to be interpreted
as unsigned integer with the most significant byte transmitted first). Each data word is immediately succeeded by an 8-bit CRC.
In write direction it is mandatory to transmit the checksum. In read direction it is up to the master to decide if it wants to process
the checksum (see Section 3.12).

3.4 Command Sequence Types
The SCD4x features four different I2C command sequence types: “read I2C sequences”, “write I2C sequences”, “send I2C
command” and “send command and fetch result” sequences. Figure 2 illustrates how the I2C communication for the different
sequence types is built-up.

Figure 2: Command sequence types: “write”, “send command”, “read”, and “send command and fetch result”

For the “read” or “send command and fetch results” sequences, after writing the address and/or data to the sensor and receiving
the ACK bit from the sensor, it is required to wait for the command execution time (see Table 9) before issuing the read header.
If a command execution time is specified in Table 9, further commands must not be sent during that command’s execution time.

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3.5 SCD4x Command Overview
An overview of the available SCD4x commands can be found in Table 9. A detailed description for each command can be foundin the following sections. Note that some commands may also be executed while a periodic measurement mode is running.
DomainBasic commands
Section 3.6

On-chip output signal
compensation
Section 3.7

Field calibration
Section 3.8

Low power periodic
measurement mode
Section 3.9

Advanced features
Section 3.10

Single shotmeasurement mode
(SCD41 only)
Section 3.11

Hex.
Code

I2C sequence type(see Section 3.4)

Execution
time
[ms]

Duringmeas.

start_periodic_measurement

0x21b1send command-noread_measurement

0xec05

read

1

yes

stop_periodic_measurement

0x3f86send command

500

yes

set_temperature_offset

0x241d

write

1

no

get_temperature_offset

0x2318

read

1

no

set_sensor_altitude

0x2427

write

1

no

get_sensor_altitude

0x2322

read

1

no

set_ambient_pressure

0xe000

write

1

yes

get_ambient_pressure

0xe000

read

1

yes

perform_forced_recalibration

0x362fsend command andfetch result

400

no

set_automatic_self_calibration_enabled

0x2416

write

1

no

get_automatic_self_calibration_enabled

0x2313

read

1

no

set_automatic_self_calibration_target

0x243a

write

1

no

get_automatic_self_calibration_target

0x233f

read

1

no

start_low_power_periodic_measurement

0x21acsend command-noget_data_ready_status

0xe4b8

read

1

yes

persist_settings

0x3615send command

800

no

get_serial_number

0x3682

read

1

no

perform_self_test

0x3639read

10’000noperform_factory_reset

0x3632

send command

1’200

no

reinit0x3646send command30

noget_sensor_variant

0x202f

read

1

no

measure_single_shot

0x219dsend command

5’000

no

measure_single_shot_rht_only

0x2196send command50

nopower_down

0x36e0send command1

nowake_up

0x36f6send command30

noset_automatic_self_calibration_initial_period

0x2445

write

1

no

get_automatic_self_calibration_initial_period

0x2340

read

1

no

set_automatic_self_calibration_standard_period

0x244e

write

1

no

get_automatic_self_calibration_standard_period

0x234b

read

1

no

Command

Table 9: List of SCD4x sensor commands. The rightmost column (‘During meas.’) indicates whether the command can be executed while aperiodic measurement mode is running.

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3.6 Basic Commands
This section lists the basic SCD4x commands that are necessary to start the periodic measurement mode and subsequently
read out the sensor outputs.
The typical communication sequence between the I2C master (e.g., a microcontroller) and the SCD4x sensor is as follows:
1. The sensor is powered up into the idle state.
2. The I2C master sends a start_periodic_measurement command. The signal update interval is 5 seconds.
3. The I2C master periodically reads out data with the read_measurement command.
4. When the sensor is to stop taking measurements periodically, the I2C master sends the stop_periodic_measurement
command to return the sensor to idle mode.
While the periodic measurement mode is running, no other commands may be issued, with exception of read_measurement,
get_data_ready_status, stop_periodic_measurement, set_ambient_pressure and get_ambient_pressure.

3.6.1

start_periodic_measurement

Description: starts the periodic measurement mode. The signal update interval is 5 seconds.
Write(hexadecimal)
0x21b1

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

-

-

-

-

Max. command
duration [ms]not applicable

Example: start periodic measurement
Write

0x21b1(hexadecimal)

Command

Table 10: start_periodic_measurement I2C sequence description

3.6.2

read_measurement

Description: reads the sensor output. The measurement data can only be read out once per signal update interval as the buffer
is emptied upon read-out. If no data is available in the buffer, the sensor returns a NACK. To avoid a NACK response, theget_data_ready_status can be issued to check data status (see Section 3.9.2 for further details). The I2C master can abort theread transfer with a NACK followed by a STOP condition after any data byte if the user is not interested in subsequent data.
Write(hexadecimal)

Response parameter: CO2, Temperature,
Relative Humidity

Input parameter: length [bytes]

signal conversion

length [bytes]
30xec05-

𝐶𝑂2 [ppm] = 𝑤𝑜𝑟𝑑[0]𝑤𝑜𝑟𝑑[1]216 − 1
𝑤𝑜𝑟𝑑[2]
𝑅𝐻 = 100 ∗ 16
2 −1

3

-

signal conversion

Max.
commandduration [ms]𝑇 = −45 + 175 ∗3

1

Example: read sensor output (500 ppm, 25 °C, 37 %RH)
Write

0xec05(hexadecimal)

Command

Wait

1 ms

Response

0x01f40x33

0x66670xa2

0x5eb90x3c(hexadecimal)

CO2 = 500 ppm

CRC of 0x01f4

Temp. = 25 °C

CRC of 0x6667

RH = 37%

CRC of 0x5eb9

command execution time

Table 11: read_measurement I2C sequence descriptionwww.sensirion.com

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3.6.3stop_periodic_measurement

Description: Command returns a sensor running in periodic measurement mode or low power periodic measurement modeback to the idle state, e.g. to then allow changing the sensor configuration or to save power. Note that the sensor will only
respond to other commands 500 ms after the stop_periodic_measurement command has been issued.
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x3f86

-

-

-

-

500

Example: stop periodic measurement
Write

0x3f86(hexadecimal)

Command

Table 12: stop_periodic_measurement I2C sequence description

3.7 On-Chip Output Signal Compensation
The SCD4x features on-chip signal compensation to automatically counteract temperature and humidity effects on CO2
measurements. Additionally, it is possible to provide the sensor with externally obtained pressure or altitude values to enableon-board compensation of the CO2 output signal for pressure variations. Furthermore, it is possible to improve the accuracy of
the relative humidity and temperature output signal by adjusting the temperature offset parameter for the design-in of the sensor.
Note that the temperature offset does not impact the accuracy of the CO2 output.
To change or read sensor settings, the SCD4x must be in the idle state (exception: ambient pressure parameters). A typicalsequence between the I2C master and the SCD4x is described as follows:
1. If the sensor is operated in a periodic measurement mode, the I2C master sends a stop_periodic_measurement command.
2. The I2C master sends one or several commands to get or set sensor settings / parameters.
3. If changes shall be retained across power-cycles, the persist_settings command must be sent (see Section 3.10.1)
4. The I2C master sends a start_periodic_measurement command to set the sensor in the operating mode again.

3.7.1

set_temperature_offset

Description: Setting the temperature offset of the SCD4x inside the customer device allows the user to optimize the RH and T
output signal. The temperature offset can depend on several factors such as the SCD4x measurement mode, self-heating ofclose components, the ambient temperature and air flow. Thus, the SCD4x temperature offset should be determined after
integration into the final device and under its typical operating conditions (including the operation mode to be used in theapplication) in thermal equilibrium. By default, the temperature offset is set to 4 °C. To save the setting to the EEPROM, thepersist_settings (see Section 3.10.1) command may be issued. Equation (1) details how the characteristic temperature offset
can be calculated using the current temperature output of the sensor (𝑇𝑆𝐶𝐷4𝑥 ), a reference temperature value (𝑇𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 ),and the previous temperature offset (𝑇𝑜𝑓𝑓𝑠𝑒𝑡_𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠 ) obtained using the get_temperature_offset command (Section 3.7.2) .
Recommended temperature offset values are between 0 °C and 20 °C.
(1)𝑇𝑜𝑓𝑓𝑠𝑒𝑡_𝑎𝑐𝑡𝑢𝑎𝑙 = 𝑇𝑆𝐶𝐷4𝑥 − 𝑇𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 + 𝑇𝑜𝑓𝑓𝑠𝑒𝑡_ 𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠
Write(hexadecimal)

Input parameter: Offset temperature

0x241d3

length [bytes]

Response parameter: -signal conversion
𝑤𝑜𝑟𝑑[0] = 𝑇𝑜𝑓𝑓𝑠𝑒𝑡 [°𝐶] ∗216 −1

length [bytes]

signal conversion--

Max. command
duration [ms]1

175

Example: set temperature offset to 5.4 °C
Write

0x241d

0x07e60x48(hexadecimal)

CommandToffset = 5.4 °C

CRC of 0x7e6

Table 13: set_temperature_offset I2C sequence descriptionwww.sensirion.com

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3.7.2

get_temperature_offset
Max.
commandduration [ms]Write(hexadecimal)

Input parameter: -Response parameter: Offset temperature

length [bytes]

signal conversion

length [bytes]

signal conversion

0x2318--3

𝑇𝑜𝑓𝑓𝑠𝑒𝑡 [°𝐶] = 𝑤𝑜𝑟𝑑[0] ∗ 16

1

175

2

−1

Example: temperature offset is 6.2 °C
Write

0x2318(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x09120x63(hexadecimal)

Toffset = 6.2 °C

CRC of 0x0912

Table 14: get_temperature_offset I2C sequence description

3.7.3

set_sensor_altitude

Description: Reading and writing the sensor altitude must be done while the SCD4x is in idle mode. Typically, the sensor
altitude is set once after device installation. To save the setting to the EEPROM, the persist_settings (see Section 3.10.1)
command must be issued. The default sensor altitude value is set to 0 meters above sea level. Valid input values are between
0 – 3’000 m.
Write(hexadecimal)

Input parameter: Sensor altitude

Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x2427

3

word[0] = Sensor altitude [m]

-

-

1

Example: set sensor altitude to 1’950 m
Write

0x24270x079e0x09(hexadecimal)

CommandSensor altitude = 1’950 m

CRC of 0x079e

Table 15: set_sensor_altitude I2C sequence description

3.7.4

get_sensor_altitude

Description: The get_sensor_altitude command can be sent while the SCD4x is in idle mode to read out the previously saved
sensor altitude value set by the set_sensor_altitude command.
Write(hexadecimal)

Input parameter: -Response parameter: Sensor altitudelength [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x2322--

3

Sensor altitude [m] = word[0]1

Example: sensor altitude is 1’100 m
Write

0x2322(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x044c0x42(hexadecimal)

Sensor altitude = 1’100 m

CRC of 0x044c

Table 16: get_sensor_altitude I2C sequence descriptionwww.sensirion.com

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3.7.5

set_ambient_pressure

Description: The set_ambient_pressure command can be sent during periodic measurements to enable continuous pressurecompensation. Note that setting an ambient pressure overrides any pressure compensation based on a previously set sensor
altitude. Use of this command is highly recommended for applications experiencing significant ambient pressure changes toensure sensor accuracy. Valid input values are between 70’000 – 120’000 Pa. The default value is 101’300 Pa.
Write(hexadecimal)

Input parameter: Ambient pressure

Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0xe0003

word[0] = ambient P [Pa] / 100

-

-

1

Example: set ambient pressure to 98’700 Pa
Write

0xe0000x03db0x42(hexadecimal)

Command

Ambient P = 98’700 Pa

CRC of 0x03db

Table 17: set_ambient_pressure I2C sequence description

3.7.6

get_ambient_pressure

Description: The get_ambient_pressure command can be sent during periodic measurements to read out the previously
saved ambient pressure value set by the set_ambient_pressure command.
Write(hexadecimal)

Input parameter: -Response parameter: Ambient pressure

length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0xe000--3

ambient P [Pa] = word[0] * 100

1

Example: ambient pressure is 98’700 Pa
Write

0xe000(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x03db0xb6(hexadecimal)

Ambient P = 98’700 Pa

CRC of 0x03db

Table 18: get_ambient_pressure I2C sequence descriptionwww.sensirion.com

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3.8 Field Calibration
To achieve high initial and excellent long-term accuracy, the SCD4x includes two field calibration features: Forced recalibration(FRC) and automatic self-calibration (ASC).
The ASC enables excellent long-term stability of SCD4x without the need for regular user intervention. The algorithm leverages
the sensor’s measurement history and the assumption of exposure of the sensor to a known minimum background CO2
concentration at least once over a period of cumulative operation. By default, the ASC algorithm assumes that the sensor is
exposed to outdoor fresh air at 400 ppm CO2 concentration at least once per week of accumulated operation using one of thefollowing measurement modes for at least 4 hours without interruption at a time: periodic measurement mode (Section 3.6), lowpower periodic measurement mode (Section 3.9) or single shot mode with a measurement interval of 5 minutes (SCD41 only,
see Section 3.11).
Performing FRC restores high accuracy by providing the SCD4x with an externally obtained CO2 reference value. FRC can beapplied to quickly correct the sensor’s output, e.g. if it is not possible to wait for and/or rely on ASC.

3.8.1

perform_forced_recalibration

Description: To successfully conduct an accurate FRC, the following steps need to be carried out:
1. Operate the SCD4x in the operation mode later used for normal sensor operation (e.g. periodic measurement) for at least
3 minutes in an environment with a homogenous and constant CO2 concentration. The sensor must be operated at thevoltage desired for the application when performing the FRC sequence.
2. Issue the stop_periodic_measurement command. Wait 500 ms for the command to complete.
3. Issue the perform_forced_recalibration command and optionally read out the FRC correction (i.e. the magnitude of thecorrection) after waiting for 400 ms for the command to complete. A return value of 0xffff indicates that the FRC has failed
because the sensor was not operated before sending the command.
Write(hexadecimal)

Input parameter: Target CO2 concentration

Response parameter: FRC-correction

length [bytes]

signal conversion

length [bytes]

signal conversion

0x362f3

word[0] = Target
concentration [ppm CO2]

3

FRC correction [ppm CO2]
= word[0] – 0x8000

Max.
commandduration [ms]400

word[0] = 0xffff in case of
failed FRC
Example: perform forced recalibration, reference CO2 concentration is 480 ppm
Write

0x362f0x01e00xb4(hexadecimal)

Command

Input: 480 ppm

CRC of 0x01e0

Wait

400 mscommand execution time

Response

0x7fce0x7b(hexadecimal)

Response: - 50 ppm

CRC of 0x7fce

Table 19: perform_forced_recalibration I2C sequence descriptionwww.sensirion.com

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3.8.2

set_automatic_self_calibration_enabled

Description: sets the current state (enabled / disabled) of the ASC. By default, ASC is enabled. To save the setting to the
EEPROM, the persist_settings (see Section 3.10.1) command must be issued.
Write(hexadecimal)

Input parameter: ASC enabled

Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x2416

3

word[0] = 1 → ASC enabledword[0] = 0 → ASC disabled

-

-

1

Example: set ASC status: enabledWrite

0x24160x00010xb0(hexadecimal)

CommandASC enabled

CRC of 0x0001

Table 20: set_automatic_self_calibration_enabled I2C sequence description.

3.8.3

get_automatic_self_calibration_enabledWrite(hexadecimal)

Input parameter: -Response parameter: ASC enabled

length [bytes]

signal conversion

length [bytes]

signal conversion

0x2313--

3

word[0] = 1 → ASC enabledword[0] = 0 → ASC disabled

Max. command
duration [ms]1

Example: read ASC status: disabled
Write

0x2313(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x00000x81(hexadecimal)

ASC disabled

CRC of 0x0000

Table 21: get_automatic_self_calibration_enabled I2C sequence description

3.8.4

set_automatic_self_calibration_target

Description: sets the value of the ASC baseline target, i.e. the CO2 concentration in ppm which the ASC algorithm will assume
as lower-bound background to which the SCD4x is exposed to regularly within one ASC period of operation. To save the setting
to the EEPROM, the persist_settings (see Section 3.10.1) command must be issued subsequently.
Write(hexadecimal)

Input parameter: -Response parameter:

length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x243a3

word[0] = ASC target [ppm CO2]

-

-

1

Example: Set ASC target to 435 ppm
Write

0x243a0x01b30x99(hexadecimal)

Command

ASC target = 435 ppm

CRC of 0x01b3

Table 22: set_automatic_self_calibration_target I2C sequence descriptionwww.sensirion.com

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3.8.5

get_automatic_self_calibration_target

Description: reads out the ASC baseline target concentration parameter. The factory default value is 400 ppm.
Write(hexadecimal)

Input parameter: -Response parameter: ASC baseline target

length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x233f--3

word[0] = ASC target [ppm CO2]

1

Example: ASC target is 420 ppm
Write

0x233f(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x01a40x4d(hexadecimal)

ASC target is 420 ppm

CRC of 0x01a4

Table 23: get_automatic_self_calibration_target I2C sequence description

3.9 Low Power Periodic Measurement Mode
To enable use-cases with a constrained power budget, the SCD4x features a low power periodic measurement mode with asignal update interval of approximately 30 seconds. The low power periodic measurement mode is initiated using thestart_low_power_periodic_measurement command and read-out in a similar manner as the periodic measurement mode using
the read_measurement command. Please consult Section 3.6.2 for further instructions.
To periodically check whether a new measurement result is available for read out, the get_data_ready_status command (Section
3.9.2) can be used to synchronize to the sensor’s internal measurement interval as an alternative to relying on the ACK/NACK
status of the read_measurement_command (Section 3.6.2)

3.9.1

start_low_power_periodic_measurement

Description: starts the low power periodic measurement mode. The signal update interval is approximately 30 seconds.
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x21ac----not applicable

Example: start low power periodic measurement
Write

0x21ac(hexadecimal)

Command

Table 24: start_low_power_periodic_measurement I2C sequence descriptionwww.sensirion.com

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3.9.2

get_data_ready_status

Description: polls the sensor for whether data from a periodic or single shot measurement is ready to be read out.
Write(hexadecimal)

Input parameter: -Response parameter: data ready status

length [bytes]

signal conversion

length [bytes]

signal conversion

0xe4b8--3

If the least significant 11 bits of word[0] are:
0 → data not readyelse → data ready for read-out

Max. command
duration [ms]1

Example: read data ready status: data not readyWrite

0xe4b8(hexadecimal)

Command

Wait

1 ms

Response

0x80000xa2(hexadecimal)

Least significant 11 bits are 0 → data
not ready

CRC of 0x8000

command execution time

Table 25: get_data_ready_status I2C sequence description

3.10 Advanced Features
3.10.1

persist_settings

Description: Configuration settings such as the temperature offset, sensor altitude and the ASC enabled/disabled parameters
are by default stored in the volatile memory (RAM) only. The persist_settings command stores the current configuration in the
EEPROM of the SCD4x, ensuring the current settings persist after power-cycling. To avoid unnecessary wear of the EEPROM,
the persist_settings command should only be sent following configuration changes whose persistence is required. The EEPROM
is guaranteed to withstand at least 2000 write cycles. Note that field calibration history (i.e. FRC and ASC, see Section 3.8) is
automatically stored in a separate EEPROM dimensioned for the specified sensor lifetime when operated continuously in either
periodic measurement mode (see Section 3.5.1), low power periodic measurement mode (see Section 3.9) or single shot modewith 5 minute measurement interval (SCD41 only, see Section 3.11).
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x3615

-

-

-

-

800

Example: persist settings
Write

0x3615(hexadecimal)

Command

Table 26: persist_settings I2C sequence descriptionwww.sensirion.com

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3.10.2

get_serial_number

Description: Reading out the serial number can be used to identify the chip and to verify the presence of the sensor.
The get_serial_number command returns 3 words, and every word is followed by an 8-bit CRC checksum. Together, the 3 words
constitute a unique serial number with a length of 48 bits (in big endian format).
Write(hexadecimal)

Input parameter: -Response parameter: serial number

length [bytes]

signal conversion

length [bytes]

signal conversion

0x3682--

9

Serial number = word[0] << 32 |word[1] << 16 | word[2]Max. command
duration [ms]1

Example: serial number is 273’325’796’834’238
Write

0x3682(hexadecimal)

Command

Wait

1 ms

Response

0xf8960x31

0x9f070xc2

0x3bbe0x89(hexadecimal)

word[0]

CRC of 0xf896

word[1]

CRC of 0x9f07

word[2]

CRC of 0x3bbe

command execution time

Table 27: get_serial_number I2C sequence description

3.10.3

perform_self_test

Description: The perform_self_test command can be used as an end-of-line test to check the sensor functionality.
Write(hexadecimal)
0x3639Input parameter: -Response parameter: sensor status

length[bytes]signal conversion

length [bytes]

signal conversion

-

-

3

word[0] = 0 → no malfunction detected
word[0] ≠ 0 → malfunction detected

Max. command
duration [ms]10’000

Example: perform self-test, no malfunction detected
Write

0x3639(hexadecimal)

Command

Wait

10000 ms

Response

0x00000x81(hexadecimal)

No malfunction detected

CRC of 0x0000

command execution time

Table 28: perform_self_test I2C sequence description

3.10.4

perfom_factory_reset

Description: The perform_factory_reset command resets all configuration settings stored in the EEPROM and erases the
FRC and ASC algorithm history.
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x3632

-

-

-

-

1’200

Example: perform factory reset
Write

0x3632(hexadecimal)

Command

Table 29: perform_factory_reset I2C sequence descriptionwww.sensirion.com

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3.10.5

reinitDescription: The reinit command reinitializes the sensor by reloading user settings from EEPROM. The sensor must be in theidle state before sending the reinit command. If the reinit command does not trigger the desired re-initialization, a power-cycle
should be applied to the SCD4x.
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x3646

-

-

-

-

30

Example: reinit
Write

0x3646(hexadecimal)

Command

Table 30: reinit I2C sequence description

3.10.6get_sensor_variant

Description: reads out the SCD4x sensor variant (e.g. SCD40 or SCD41).
Write(hexadecimal)

Input parameter: -Response parameter: sensor variant

length [bytes]

signal conversion

length [bytes]

signal conversion

0x202f--3

Word[0]:Bits[15…12] = 0000 → SCD40
Bits[15…12] = 0001 → SCD41

Write

0x202f(hexadecimal)

Command

Wait

1 ms

Max. command
duration [ms]1command execution time

Example: sensor variant is SCD41. Response bits 0…11 may differ from this example
Response

0x14400x51(hexadecimal)

Product version = SCD41

CRC of 0x1440

Example: sensor variant is SCD40. Response bits 0…11 may differ from this example
Response

0x04400x3F(hexadecimal)

Product version = SCD40

CRC of 0x0440

Table 31: get_sensor_variant I2C sequence descriptionwww.sensirion.com

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3.11 Single Shot Measurement Mode (SCD41 Only)
The SCD41 additionally features a single shot measurement mode for on-demand measurements.
The typical communication sequence is as follows:
1. The sensor is powered up with the wake_up command if previously powered down using the power_down command.
2. The I2C master sends a measure_single_shot command and waits for the indicated max. command duration time.
3. The I2C master reads out data with the read_measurement command (3.6.2) after the specified max. command durationtime.
4. Repeat steps 2–3 as required by the application.
5. If desired, power down the sensor with the power_down command.
To reduce noise levels, the I2C master can perform several single shot measurements in a row and average the CO2 output
values. Note: The fastest possible sampling interval for single shot measurements is 5 seconds.
The ASC is enabled by default in single shot operation and optimized for single shot measurements performed every 5 minutes.
Longer or shorter single shot measurement intervals will result in less or more frequent ASC corrections, respectively. To adapt
the ASC parameters for measurement intervals other than 5 minutes, the ASC initial and standard period length parameters canbe adjusted (see relevant commands in following subsections and relevant supporting documentation18). The standard period
represents the cumulative duration of the sensor in measurement mode, tracked in blocks of 4 hours, periodically triggering
automatic self-calibration. If operated for the very first time, or following a perform_factory_reset command, the shorter initialperiod parameter is used exactly and only once.
Note that, for single shot operation with ASC enabled and measurement intervals of less than 5 minutes, the lifetime of EEPROM
used by the ASC is reduced proportionally.
To further reduce the sensor’s power consumption, the sensor may be power cycled between measurements either by cutting/reapplying the supply and I2C voltages or by using the power_down/wake_up commands. Note that for power-cycled single shot
operation, ASC functionality is not available in either case.

3.11.1

measure_single_shot

Description: on-demand measurement of CO2 concentration, relative humidity and temperature. The sensor output is read out
by using the read_measurement command (Section 3.6.2).
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x219d

-

-

-

-

5’000

Example: measure single shot
Write

0x219d(hexadecimal)

Command

Table 32: measure_single_shot I2C sequence description

18 More information on ASC settings and SCD4x low power modes can be found in the application note on “Low Power Operation SCD4x”

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3.11.2

measure_single_shot_rht_only

Description: on-demand measurement of relative humidity and temperature only, significantly reduces power consumption. The
sensor output is read out by using the read_measurement command (Section 3.6.2). CO2 output is returned as 0 ppm.
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x2196

-

-

-

-

50

Example: measure single shot, RH and T output only
Write

0x2196(hexadecimal)

Command

Table 33: measure_single_shot_rht_only I2C sequence description

3.11.3

power_down

Description: put the sensor from idle to sleep to reduce current consumption. Can be used to power down when operating thesensor in power-cycled single shot mode.
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x36e0

-

-

-

-

1

Example: power down the sensor
Write

0x36e0(hexadecimal)

Command

Table 34: power_down I2C sequence description

3.11.4

wake_up

Description: wake up the sensor from sleep mode into idle mode. Note that the SCD4x does not acknowledge the wake_up
command. The sensor’s idle state after wake up can be verified by reading out the serial number (Section 3.10.2).
Write(hexadecimal)

Input parameter: -Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x36f6

-

-

-

-

30

Example: wake up the sensor
Write

0x36f6(hexadecimal)

Command

Table 35: wake_up I2C sequence descriptionwww.sensirion.com

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3.11.5

set_automatic_self_calibration_initial_period

Description: sets the duration of the initial period for ASC correction (in hours). By default, the initial period for ASC correctionis 44 hours. Allowed values are integer multiples of 4 hours. A value of 0 results in an immediate correction. To save the setting
to the EEPROM, the persist_settings (see Section 3.10.1) command must be issued.
Note: For single shot operation, this parameter always assumes a measurement interval of 5 minutes, counting the number ofsingle shots to calculate elapsed time. If single shot measurements are taken more / less frequently than once every 5 minutes,
this parameter must be scaled accordingly to achieve the intended period in hours (e.g. for a 10-minute measurement interval,
the scaled parameter value is obtained by multiplying the intended period in hours by 0.5).
Write(hexadecimal)

Input parameter: ASC initial period

Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x2445

3

word[0] = ASC initial period[hours]--1

Example: write ASC initial period of 76 hours
Write

0x24450x004c0xc1(hexadecimal)

Command

Initial period
76 hours

CRC of 0x004c

Table 36: set_automatic_self_calibration_initial_period I2C sequence description

3.11.6

get_automatic_self_calibration_initial_periodWrite(hexadecimal)

Input parameter: -Response parameter: ASC initial period

length [bytes]

signal conversion

length [bytes]

signal conversion

0x2340--3

ASC initial period [hours] =word[0]Max. command
duration [ms]1

Example: read ASC initial period of 76 hours
Write

0x2340(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x004c0xc1(hexadecimal)

76 hours

CRC of 0x004c

Table 37: get_automatic_self_calibration_initial_period I2C sequence descriptionwww.sensirion.com

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3.11.7

set_automatic_self_calibration_standard_period

Description: sets the standard period for ASC correction (in hours). By default, the standard period for ASC correction is 156
hours. Allowed values are integer multiples of 4 hours. Note: a value of 0 results in an immediate correction. To save thesetting to the EEPROM, the persist_settings (see Section 3.10.1) command must be issued.
Note: For single shot operation, this parameter always assumes a measurement interval of 5 minutes, counting the number ofsingle shots to calculate elapsed time. If single shot measurements are taken more / less frequently than once every 5 minutes,
this parameter must be scaled accordingly to achieve the intended period in hours (e.g. for a 10-minute measurement interval,
the scaled parameter value is obtained by multiplying the intended period in hours by 0.5).
Write(hexadecimal)
0x244eInput parameter: ASC standard period

Response parameter: -length [bytes]

signal conversion

length[bytes]signal conversion

Max. command
duration [ms]3word[0] = ASC standard period[hours]--1

Example: set automatic self-calibration standard period of 156 hours
Write

0x244e0x009c0xc5(hexadecimal)

CommandStandard
period156 hours

CRC of 0x009c

Table 38: set_automatic_self_calibration_standard_period I2C sequence description

3.11.8get_automatic_self_calibration_standard_periodWrite(hexadecimal)

Input parameter: -Response parameter: ASC standard period

length [bytes]

signal conversion

length [bytes]

signal conversion

0x234b--3

word[0] = ASC standard
period [hours]

Max. command
duration [ms]1

Example: read ASC standard period of 156 hours
Write

0x234b(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x009c0xc5(hexadecimal)

Standard period
156 hours

CRC of 0x009c

Table 39: get_automatic_self_calibration_standard_period I2C sequence descriptionwww.sensirion.com

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3.12 Checksum Calculation
The 8-bit CRC checksum transmitted after each data word is generated by a CRC algorithm. Its properties are displayed inTable 40. The CRC covers the contents of the two previously transmitted data bytes. To calculate the checksum only these two
previously transmitted data bytes are used. Note that command words are not followed by CRC.
Property

Value

Example code (C/C++)

Name

CRC-8

Width

8 bit

#define CRC8_POLYNOMIAL 0x31
#define CRC8_INIT 0xff

Protected Dataread and/or write data

Polynomial

0x31 (x8 + x5 + x4 + 1)

Initialization

0xff

Reflect input

False

Reflect output

False

Final XOR

0x00

ExamplesCRC (0xbeef) = 0x92

uint8_t sensirion_common_generate_crc(const uint8_t* data, uint16_t count) {uint16_t current_byte;
uint8_t crc = CRC8_INIT;
uint8_t crc_bit;/* calculates 8-Bit checksum with given polynomial */for (current_byte = 0; current_byte < count; ++current_byte) {crc ^= (data[current_byte]);for (crc_bit = 8; crc_bit > 0; --crc_bit) {if (crc & 0x80)
crc = (crc << 1) ^ CRC8_POLYNOMIAL;
else
crc = (crc << 1);}}
return crc;}

Table 40: I2C CRC properties

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4

Mechanical Specifications

4.1 Package Outline
Figure 3 schematically displays the sensor’s package outline, as well as key nominal dimensions and their tolerances inmillimeters. A circular mark and a notched corner of the protective membrane serve as polarity marks to indicate the locationof pin 1. The white protective membrane on top of the sensor must not be removed or tampered with to ensure proper sensor
operation. The weight of the sensor is approx. 0.6 g.

Figure 3: Sensor package dimensions of SCD4x: top, side and bottom view (left to right, projection method 1). All dimensions in millimeters.

4.2 Land Pattern Recommendation
Recommended land pattern, solder paste, and solder mask are shown in Figure 4. The exact mask geometries, distances andstencil thicknesses must be adapted to the customer soldering processes. In any case, the keep-free area around the thermal
relief hole of the sensor must be respected.

Figure 4: Recommended SCD4x footprint (top view): landing pads (a), solder paste (b) and solder mask (c). All dimensions in millimeters.

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4.3 Tape & Reel Package
Figure 5 details the tape and reel package specifications. Reels are 7 inches and 13 inches in diameter for the 60-piece and
600-piece package sizes, respectively.

Figure 5: Technical drawing of the packaging tape with sensor orientation in tape. In the drawing, header tape is to the right and trailer tapeto the left. All dimensions in millimeters.

4.4 Moisture Sensitivity Level
Sensirion SCD4x sensors must be treated according to Moisture Sensitivity Level 1 (MSL1) as per IPC/JEDEC J-STD-033B1.
The manufacturing floor time (out of bag) at the customer’s end is not limited under normal factory conditions (≤30 °C and 85%RH). It is recommended to process the sensors within one year of the date of delivery. Exposure to moisture levels or solder
reflow temperatures which exceed the limits as stated in this document can result in yield loss and reliability degradation19.

19 More information on SCD4x packing and storage can be found in the user guide “Handling Instructions SCD4x”

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4.5 Soldering Instructions
The sensors are designed to withstand a soldering profile based on IPC/JEDEC J-STD-020, with a maximum peak temperatureof 245 °C up to 30 sec and Pb-free assembly in IR/Convection reflow ovens. See Table 41 for more details.
Note that due to the size and shape of the SCD4x sensor, significant temperature differences across the sensor element canoccur during reflow soldering. Specifically, the temperature within the sensor cap can be higher than the temperature measured
at the pad using usual temperature monitoring methods. Care must be taken that a temperature of 245°C is not exceeded at
any time in any part of the sensor.
The SCD4x is not compatible with vapor phase reflow soldering. The dust cover on top of the cap must not be removed or wettedwith any liquid. Do not apply extra flux during the reflow soldering nor reflow solder more than once. Do not apply any board
wash process step subsequently to the reflow soldering20.
Minor temporary accuracy deviations of the CO2 reading can result from the reflow soldering of the SCD4x. Full sensor accuracy
is restored after at most five days after the soldering process, independently of whether the sensor is operated or not.
Average ramp-up rate

< 3 °C / second

Liquid phase
▪ TL
▪ tL

> 220 °C
< 60 seconds

Peak temperature
▪ TP
▪ tP

≤ 245°C< 30 seconds

Ramp-down rate

< 4 °C / second fortemperature > TL

Table 41: Soldering profile parameters

4.6 Traceability and Identification
All SCD4x sensors have a distinct electronic serial number for identification and traceability (see Section 3.10.2). The serial
number can be decoded by Sensirion only and allows for tracking through production, calibration, and testing.
All SCD4x sensors include a laser marking on the sidewall of the sensor cap. The laser marking contains the product variant(i.e., SCD40 or SCD41) and the product serial number within a data matrix (Figure 6).

Figure 6: Technical drawing of the laser marking of product type and data matrix on the sidewall of the sensor cap.

20 More information on SCD4x reflow soldering can be found in the user guide “Handling Instructions SCD4x”

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5

Ordering Information

Use the part names and product numbers shown in Table 42 when ordering the SCD4x CO2 sensor. For the latest productinformation and local distributors, please visit the Sensirion website.
Part Name
SCD40-D-R1
SCD40-D-R2
SCD41-D-R1
SCD41-D-R2
SEK-SCD41-Sensor
SEK-SensorBridge

Description
SCD40 CO2 sensor SMD component as reel, I2C
SCD40 CO2 sensor SMD component as reel, I2C
SCD41 CO2 sensor SMD component as reel, I2C
SCD41 CO2 sensor SMD component as reel, I2C
SEK-SCD41-Sensor set; SCD41 on development
board with cables
Sensor Bridge to connect SEK-SCD41-Sensor tocomputer

Ordering quantity (pcs)
60 sensors per reel
600 sensors per reel60 sensors per reel
600 sensors per reel
1

Product Number
3.000.496
3.000.521
3.000.960
3.000.961
3.000.455

1

3.000.124

Table 42: Active part names and product numbers for ordering SCD4x5.1 Historical Information
The parts / product numbers of the SCD4x product family shown in Table 43 are obsolete.
Period Active
Before 01.08.2023
Before 01.08.2023

Product Number
3.000.497
3.000.498

Note
For applicable specifications, see Version 1.3 of the SCD4x Datasheet
For applicable specifications, see Version 1.3 of the SCD4x Datasheet

Table 43: Obsolete ordering informationwww.sensirion.com

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Revision History

Date
January 2021
April 2021

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Changes
Initial release
Adjustment max. command time self-test (Section 3.9) and single shot (Section 3.10),
minor revisions on other pages
Clarification on additional sensor accuracy drift (Table 1)
Clarification of set_ambient_pressure command description (Section 3.7.5)
Addition of power_down and wake_up commands (Section 3.11)
Addition of minor temporary accuracy deviation after reflow soldering (Section 4.5)
Minor editorial revisions
Correction of hyperlink
Minor editorial revisions
Updated SCD41 accuracy values, updated drift parameters and drift conditions (Table 1),
correction of tolerance in footnote #2, clarification of footnotes #2, 4 and 5
Clarification of operation mode per average supply current (Table 4), additional information
on ESD HBM (Table 5), additional footnote #8, clarification of footnotes #7 and 12
Clarification of recommendations on power supply for sensor operation (Section 2.3)
Correction of power-up time and soft reset time, increase of maximum SCL clock frequency
to 400 kHz (Section 2.4)
Minor editorial revisions for clarification (Section 3.1)
Addition of get_ambient_pressure, set_automatic_self_calibration_initial_period,
get_automatic_self_calibration_initial_period,
set_automatic_self_calibration_standard_period,
get_automatic_self_calibration_standard_period and set_automatic_self_calibration_target
commands (Table 9), correction of reinit and wake_up execution times (Section 3.4)
Addition of recommended temperature offset range, formula correction of signal conversion(Section 3.6.1)
Formula correction of signal conversion (Section 3.6.2), addition of valid sensor altitude
input values (Section 3.6.3)
Addition of valid ambient pressure input values to set_ambient_pressure command(Section 3.6.5) and addition of get_ambient_pressure command (Section 3.6.6)
Correction of reinit max. command duration (Section 3.9.5), clarification of typicalcommunication sequence for single shot measurement mode (Section 3.10)
Correction of wake_up max. command duration (Section 3.10.4), addition of
set_automatic_self_calibration_initial_period (Section 3.10.5) and
get_automatic_self_calibration_initial_period commands (Section 3.10.6)
Addition of set_automatic_self_calibration_standard_period command (Section 3.10.7) and
get_automatic_self_calibration_standard_period command (Section 3.10.8)
Additional information on white protection membrane (Section 4.1)
Increase of peak reflow soldering temperature to 245°C, clarification of soldering guidance(Section 4.5), addition of information concerning product laser marking (Section 4.6)
Minor editorial revisions
Clarified description of supply voltage ripple specification (Section 2, Table 4)
Addition of description for get_data_ready_status command (Section 3.8.2)
Clarification on ASC availability in power-cycled single shot operation (Section 3.10),
Addition of clarification on ASC period parameter scaling for single shot operation(Sections 3.10.5 and 3.10.7)
Moved dimensions into Figure 3, removed separate table with dimensions (Section 4.1)
Updated product numbers for SCD41, addition of historical ordering information (Section 5)
Minor editorial revisions
Updated visuals and product summary, corrected block diagram, added footnotes #1-3
Clarification of default conditions, clarification of conditions for response time specificationand description of drift specification (Table 1), clarified measurement mode condition for
RH/T response time specification and moved previous footnote #5 into prose text (Sections
1.2 and 1.3), clarification of footnotes #5-7(prev. footnotes 2-4).
Changed moisture sensitivity level specification to MSL Level 1 (Section 2.2, Table 5)
Clarification of footnote #15 (prev. footnote 11)

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Clarification of recommendations on power supply for sensor operation and of I2C
specification (Section 2.3)
Moved Table 8 into separate new sub-section clarifying sensor I2C address (Section 3.2)
Addition of set_automatic_self_calibration_target, get_automatic_self_calibration_target
and get_sensor_variant commands to Table 9 (Section 3.5)
Clarified typical communication sequence description (Section 3.6)
Clarified description of stop_periodic_measurement command (Section 3.6.3)
Clarified description of on-chip output signal compensation (Section 3.7) and
set_temperature_offset command (Section 3.7.1)
Clarified and expanded information on ASC functionality and conditions for use with default
parameters (Section 3.8)
Addition of set_automatic_self_calibration_target command (Section 3.8.4)
Addition of get_automatic_self_calibration_target command (Section 3.8.5)
Clarified note on EEPROM lifetime conditions for operation with ASC (Section 3.10.1)
Addition of get_sensor_variant command (Section 3.10.6)
Addition of note on shortest possible single shot measurement interval, clarified impact of
single shot measurement interval on ASC functionality and EEPROM lifetime, removed
recommendation to discard initial single shot measurement after power cycle (Section 3.11)
Clarified note on ASC initial period parameter adaption based on single shot measurement
interval (Section 3.11.5)
Clarified note on ASC standard period parameter adaption based on single shotmeasurement interval (Section 3.11.7)
Clarified note on polarity marking of the sensor, updated Figure 3 to add bottom view withrespective dimensions (Section 4.1)
Addition of note on sensor thermal relief hole and respective keep free area, updated
Figure 4 for clarity (Section 4.2)
Addition of reel diameters (Section 4.3).
Updated moisture sensitivity level specification from MSL3 to MSL1, adapted out of bag
manufacturing floor time conditions in accordance with MSL1, removed table specifying
baking conditions for MSL3 (Section 4.4)
Minor editorial revisions

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Important Notices
Warning, Personal Injury
Do not use this product as safety or emergency stop devices or in any other application where failure of the product could result inpersonal injury. Do not use this product for applications other than its intended and authorized use. Before installing, handling, using orservicing this product, please consult the data sheet and application notes. Failure to comply with these instructions could result indeath or serious injury.
If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify and holdharmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages and expenses, andreasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorizeduse, even if SENSIRION shall be allegedly negligent with respect to the design or the manufacture of the product.
ESD Precautions
The inherent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESD-induced damage and/or
degradation, take customary and statutory ESD precautions when handling this product. See application note “ESD, Latchup and EMC” for more
information.
Warranty
SENSIRION warrants solely to the original purchaser of this product for a period of 12 months (one year) from the date of delivery that this productshall be of the quality, material and workmanship defined in SENSIRION’s published specifications of the product. Within such period, if proven to
be defective, SENSIRION shall repair and/or replace this product, in SENSIRION’s discretion, free of charge to the Buyer, provided that:•
notice in writing describing the defects shall be given to SENSIRION within fourteen (14) days after their appearance;•such defects shall be found, to SENSIRION’s reasonable satisfaction, to have arisen from SENSIRION’s faulty design, material, or
workmanship;•
the defective product shall be returned to SENSIRION’s factory at the Buyer’s expense; and•the warranty period for any repaired or replaced product shall be limited to the unexpired portion of the original period.
This warranty does not apply to any equipment which has not been installed and used within the specifications recommended by SENSIRION for
the intended and proper use of the equipment. EXCEPT FOR THE WARRANTIES EXPRESSLY SET FORTH HEREIN, SENSIRION MAKES NO
WARRANTIES, EITHER EXPRESS OR IMPLIED, WITH RESPECT TO THE PRODUCT. ANY AND ALL WARRANTIES, INCLUDING WITHOUT
LIMITATION, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE EXPRESSLY EXCLUDED AND
DECLINED.
SENSIRION is only liable for defects of this product arising under the conditions of operation provided for in the data sheet and proper use of thegoods. SENSIRION explicitly disclaims all warranties, express or implied, for any period during which the goods are operated or stored not inaccordance with the technical specifications.
SENSIRION does not assume any liability arising out of any application or use of any product or circuit and specifically disclaims any and all
liability, including without limitation consequential or incidental damages. All operating parameters, including without limitation recommended
parameters, must be validated for each customer’s applications by customer’s technical experts. Recommended parameters can and do vary in
different applications.
SENSIRION reserves the right, without further notice, (i) to change the product specifications and/or the information in this document and (ii) toimprove reliability, functions and design of this product.
Copyright © 2024, by SENSIRION. CMOSens® and PASens® are trademarks of Sensirion. All rights reserved.

Headquarters and Subsidiaries
Sensirion AG
Laubisruetistr. 50
CH-8712 Staefa ZH
Switzerland

Sensirion Inc., USA
phone: +1 312 690 5858
info-us@sensirion.com
www.sensirion.com

Sensirion Korea Co. Ltd.
phone: +82 31 337 7700~3
info-kr@sensirion.com
www.sensirion.com/kr

phone: +41 44 306 40 00
fax:+41 44 306 40 30
info@sensirion.com
www.sensirion.com

Sensirion Japan Co. Ltd.
phone: +81 45 270 4506
info-jp@sensirion.com
www.sensirion.com/jp

Sensirion China Co. Ltd.
phone: +86 755 8252 1501
info-cn@sensirion.com
www.sensirion.com/cn

Sensirion Taiwan Co. Ltd
phone: +886 2 2218-6779
info@sensirion.com
www.sensirion.com

To find your local representative, please visit
www.sensirion.com/distributors

www.sensirion.com

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