SCD4x
Breaking the size barrier in CO2 sensing

Features▪ Photoacoustic sensor technology PASens®
▪ Smallest form factor: 10.1 x 10.1 x 6.5 mm3▪ Reflow solderable for cost effective assembly▪ Large output range: 0 ppm – 40’000 ppm▪ Large supply voltage range: 2.4 – 5.5 V

▪
▪
▪
▪

High accuracy: ±(40 ppm + 5 %)Digital I2C interface
Integrated temperature and humidity sensor
Low power operation down to < 0.4 mA avg.
@ 5 V, 1 meas. / 5 minutes

Product Summary
The SCD4x is Sensirion’s next generation miniature CO2
sensor. This sensor builds on the photoacoustic sensing
principle and Sensirion’s patented PAsens® andCMOSens® technology to offer high accuracy at an
unmatched price and smallest form factor. SMD assembly
allows cost- and space-effective integration of the sensor
combined with maximal freedom of design. On-chip signal
compensation is realized with the build-in SHT4x humidity
and temperature sensor.

Device Overview

CO2 is a key indicator for indoor air quality as high levels
compromise humans’ cognitive low power
and well-being. The SCD4x enables smart ventilation
systems to regulate ventilation in the most energy-efficientand human-friendly way. Moreover, indoor air quality
monitors and other connected devices based on the
SCD4x can help maintaining low CO2 concentration for ahealthy, productive environment.

Functional Block Diagram

Products
Details
SCD40-D-R2 Base accuracy, specified range
400 – 2’000 ppm
SCD41-D-R2 High accuracy, specified range
400 – 5’000 ppm, single shotmode supported
Full product list on page 21

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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 5........................................................................................................ 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 Data type & length................................................................................................................................... 7
3.3 Command Sequence Types .................................................................................................................... 7
3.4 SCD4x Command Overview .................................................................................................................... 8
3.5 Basic Commands .................................................................................................................................... 9
3.6 On-Chip Output Signal Compensation ................................................................................................... 10
3.7 Field Calibration .................................................................................................................................... 12
3.8 Low Power operation............................................................................................................................. 14
3.9 Advanced Features ............................................................................................................................... 15
3.10 Low power single shot (SCD41) ............................................................................................................ 17
3.11 Checksum Calculation ........................................................................................................................... 18
4 Mechanical specifications .......................................................................................................................... 19
4.1 Package Outline.................................................................................................................................... 19
4.2 Land Pattern ......................................................................................................................................... 19
4.3 Tape & Reel Package ........................................................................................................................... 20
4.4 Moisture Sensitivity Level ...................................................................................................................... 20
4.5 Soldering Instructions ............................................................................................................................ 21
4.6 Traceability ........................................................................................................................................... 21
5 Ordering Information .................................................................................................................................. 21
6 Revision History.......................................................................................................................................... 21

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1

Sensor Performance

1.1 CO2 Sensing Performance
Default conditions of 25 °C, 50 % RH, ambient pressure 1013 mbar, default periodic measurement and 3.3 V supply voltage
apply to values in the table below, unless otherwise stated.
Parameter
CO2 output range1
SCD40 CO2 measurement accuracy2
SCD41 CO2 measurement accuracy2
Repeatability
Response time3
Accuracy drift per year with automatic selfcalibration algorithm enabled4

Conditions
400 ppm – 2’000 ppm
400 ppm – 5’000 ppm
Typicalτ63% , typicalValue
0 – 40’000 ppm± (50 ppm + 5% of reading)± (40 ppm + 5% of reading)± 10 ppm
60 s

Typical± (5 ppm + 0.5 % of reading)

Table 1: SCD40 and SCD41 CO2 sensor specifications

1.2 Humidity Sensing Performance5
Parameter
Humidity measurement range
Accuracy (typ.)Repeatability
Response time3
Accuracy drift

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

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 Performance5
Parameter
Temperature measurement range
Accuracy (typ.)Repeatability
Response time3
Accuracy drift

Conditions
15 °C – 35 °C-10 °C – 60 °C
τ63% , typical-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

Exposure to CO2 concentrations smaller than 400 ppm can affect the accuracy of the sensor if the automatic self-calibration (ASC) is on.
Deviation to a high-precision reference. Accuracy is fulfilled by > 90% of the sensors after calibration. Rough handling, shipping and soldering reduces the accuracy of thesensor. Accuracy is restored with FRC or ASC recalibration features. Accuracy is based on tests with gas mixtures having a to lerance of ± 1.5%.
3 Time for achieving 63% of a respective step function when operating the SCD41 Evaluation Kit with default measurement mode. Response time depends on design-in,
signal update rate and environment of the sensor in the final application.
4 For proper function of ASC field-calibration algorithm SCD4x has to be exposed to air with CO 2 concentration 400 ppm regularly. Maximum accuracy drift per year estimatedfrom stress tests is ± (5 ppm + 2 % of reading). Higher drift values may occur if the sensor is not handled according to its handling instructions.
5 Design-in of the SCD4x in final application, self-heating of the sensor and the environment impacts the accuracy of the RH/T sensor. To realize indicated specifications, thetemperature-offset of the SCD4x inside the customer device must be set correctly (see chapter 3.6). Best RH/T accuracy is realized when operating the SCD4x in low power
periodic measurement mode.
1
2

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2

Specifications

2.1 Electrical Specifications
Parameter
Supply voltage DC
Voltage ripple peak to peak

Symbol Conditions
VDD
VRPP
VDD = 3.3 V
Peak supply current6
VDD = 5 V
VDD = 3.3 V
Average supply current for periodic
IDD
measurement, periodic measurement
VDD = 5 V
VDD = 3.3 V
Average supply current for periodic
IDD
measurement, low power periodic measurement
VDD = 5 V
Average supply current for periodic single shot
VDD = 3.3 V
measurement, 1 measurement / 5 minutes
IDD
VDD = 5 V
(SCD41 only)7
Input high level voltage
VIH
Input low level voltage
VIL
Output low level voltage
VOL
3 mA sink current

Min.
2.4

Typical
3.3 or 5.0
175
115
15
11
3.2
2.8
0.45
0.36

0.7 x VDD

Max.
5.5
30
205
137
18
13
3.5
3
0.5
0.4

Units
V
mV
mA
mA
mA
mA
mA
mA
mA

1 x VDD
0.3 x VDD
0.66

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 reliability of the device.
Parameter
Temperature operating conditions
Humidity operating conditions8
MSL Level
DC supply voltage
Max voltage on pins SDA, SCL, GND
Input current on pins SDA, SCL, GND
Short term storage temperature9
Recommended storage temperature
ESD HBMESD CDM
Maintenance Interval
Sensor lifetime 11

Conditions
Non-condensing

Maintenance free when ASC fieldcalibration algorithm10 is used.
Typical operating conditions

Value-10 – 60°C
0 – 95 %RH3- 0.3 V – 6.0 V– 0.3 V to VDD+0.3 V- 280 mA to 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

Power supply should be designed with respect to peak current.
On-demand measurement with freely adjustable interval. See chapter 3.10
8 Accuracy can be reduced at relative humidity levels lower than 10 %.
9 Short term storage refers to temporary conditions during e.g. transport.
10 For proper function of ASC field-calibration algorithm the SCD4x has to be exposed to clean air with 400 ppm CO concentration regularly.
2
11 Sensor tested over simulated lifetime of > 10 years for indoor environment mission profile
6
7

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2.3 Interface Specifications
The SCD4x comes in an LGA package (Table 6). The package outline is schematically displayed in chapter 4.1. The landing
pattern of the SCD4x can be found in chapter 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 apolarity 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. should both be connected tothe same power supply. The combined maximum current drawn on VDD and VDDH is indicated in Table 4. Care should betaken to choose a low noise power supply (preferably a low-dropout regulator, LDO, with output ripple of less than 30 mV p-p),which is adequately dimensioned for the relatively large peak currents. Power supply configurations with large transient voltage
drops are to be avoided to ensure proper sensor operation.
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 manual12
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 details10). It
should be noted that pull-up resistors may be included in I/O circuits of microcontrollers.

Figure 1: Typical application circuit (for better clarity in the image, the positioning of the pins does
not reflect the positions on the real sensor). VDD and VDDH must be connected to each other close
to the sensor on the customer PCB.

12 http://www.nxp.com/documents/user_manual/UM10204.pdf

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2.4 Timing Specifications
Table 7 list the timings of the ASIC part and does not reflect the availability or usefulness of the sensor readings. The SCD4x
supports the I2C “standard-mode” as is described elsewhere (see footnote 12).
Parameter

Condition

Min.

Max.

Unit

Power-up time

After hard reset, VDD ≥ 2.25 V

-

1000

ms

Soft reset time

After re-initialization (i.e. reinit)

-

1000

ms

SCL clock frequency

-

0

100

kHz

Table 7 System timing specifications.

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

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3

Digital Interface Description

All SCD4x commands and data are mapped to a 16-bit address space.
SCD4x

Hex. CodeI2C address

0x62

Table 8 I2C device address.

3.1 Power-Up and Communication Start
The sensor starts powering-up after reaching the power-up threshold voltage VDD,Min = 2.25 V. After reaching this thresholdvoltage, the sensor needs 1000 ms to enter the idle state. Once the idle state is entered it is ready to receive commands fromthe 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 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, 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 thechecksum (see chapter 3.11).

3.3 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” sequence, “send command” sequence, “read”
sequence, and “send command and fetch result” sequence.

For “read”” or “send command and fetch results” sequences, after writing the address and/or data to the sensor and sending the
ACK bit, the sensor needs the execution time (see Table 9) to respond to the I2C read header with an ACK bit. Hence, it isrequired to wait the command execution time before issuing the read header. Commands must not be sent while a previous
command is being processed.
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3.4 SCD4x Command Overview
Table 9: List of SCD4x sensor commands. Detailed description of SCD4x commands can be foundfurther down. *Column indicates whether command can be executed while a periodic measurement
is running.
DomainBasic Commands
Chapter 3.5

On-chip output signal
compensation
Chapter 3.6

Field calibration
Chapter 3.7
Low power
Chapter 3.8

Advanced features
Chapter 3.9

Low power single shot
(SCD41 only) Chapter 3.10

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CommandHex.
Code

I2C sequence type(see chapter 3.3)

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

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

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

0x3639

read

10000

no

perform_factory_reset

0x3632

send command

1200

no

reinit0x3646send command

20

nomeasure_single_shot

0x219dsend command

5000

no

measure_single_shot_rht_only

0x2196send command

50

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3.5 Basic Commands
This section lists the basic SCD4x commands that are necessary to start a periodic measurement 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
2. The I2C master sends a start_periodic_measurement command. Signal update interval is 5 seconds.
3. The I2C master periodically reads out data with the read measurement sequence.
4. To put the sensor back to idle mode, the I2C master sends a stop periodic measurement command.
While a periodic measurement is running, no other commands must be issued with the exception of read_measurement,
get_data_ready_status, stop_periodic_measurement and set_ambient_pressure.

3.5.1

start_periodic_measurement

Description: start periodic measurement, signal update interval is 5 seconds.
Table 10: start_periodic_measurement I2C sequence description
Write(hexadecimal)

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

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x21b1----

not applicable

Example: start periodic measurement
Write

0x21b1(hexadecimal)

Command3.5.2

read_measurement

Description: read 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 chapter 3.8.2 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.
Table 11: read_measurment I2C sequence description

Write(hexadecimal)

0xec05

Response parameter: CO2, Temperature, Relative
Humidity

Input parameter: length [bytes]

signal conversion--

length [bytes]

signal conversion

3

CO2 [ppm] = word[0]3

T = - 45 + 175 * word[1] / 2 16

3

RH = 100 * word[2] / 2 16

Max.
commandduration [ms]1

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

0xec05(hexadecimal)

Command

Wait

1 ms

Response

0x01f40x7b0x66670xa2

0x5eb90x3c(hexadecimal)

CO2 = 500 ppm

CRC of 0x01f4

Temp. = 25 °C

CRC of 0x6667

RH = 37 %CRC of 0x5eb9

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command execution time

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3.5.3stop_periodic_measurement

Description: stop periodic measurement to change the sensor configuration or to save power. Note that the sensor will only
respond to other commands after waiting 500 ms after issuing the stop_periodic_measurement command.
Table 12: stop_periodic_measurement I2C sequence description
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

3.6 On-Chip Output Signal Compensation
The SCD4x features on-chip signal compensation to counteract pressure and temperature effects. Feeding the SCD4x with thepressure or altitude enables highest accuracy of the CO 2 output signal across a large pressure range. Setting the temperatureoffset improves the accuracy of the relative humidity and temperature output signal. 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 idle mode. A typical sequence 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 the sensor settings.
3. If configurations shall be preserved after power-cycle events, the persist_settings command must be sent (seechapter 3.9.1)
4. The I2C master sends a start measurement command to set the sensor in the operating mode again.

3.6.1

set_temperature_offset
Description: The temperature offset has no influence on the SCD4x CO2 accuracy. Setting the temperature offset of the SCD4xinside the customer device correctly allows the user to leverage the RH and T output signal. Note that the temperature offset
can depend on various factors such as the SCD4x measurement mode, self-heating of close components, the ambient
temperature and air flow. Thus, the SCD4x temperature offset should be determined inside the customer device under its typicaloperation conditions (including the operation mode to be used in the application) and in thermal equilibrium. Per default, thetemperature offset is set to 4° C. To save the setting to the EEPROM, the persist setting (see chapter 3.9.1) command must be
issued. Equation (1) shows how the characteristic temperature offset can be obtained.
(1)

𝑇𝑜𝑓𝑓𝑠𝑒𝑡_𝑎𝑐𝑡𝑢𝑎𝑙 = 𝑇𝑆𝐶𝐷40 − 𝑇𝑅𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 + 𝑇𝑜𝑓𝑓𝑠𝑒𝑡_ 𝑝𝑟𝑒𝑣𝑖𝑜𝑢𝑠
Table 13: set_temperature_offset I 2C sequence description
Write(hexadecimal)

Input parameter: Offset temperature

Response parameter: -length [bytes]

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x241d3

word[0] = T offset [°C] * 216 / 175

-

-

1

Example: set temperature offset to 5.4 °C
Write

0x241d

0x07e60x48(hexadecimal)

CommandToffset = 5.4 °C

CRC of 0x7e6

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3.6.2

get_temperature_offset

Table 14: get_temperature_offset I 2C sequence description
Write(hexadecimal)

Input parameter: length [bytes]

signal conversion

length [bytes]

signal conversion

Max.
commandduration [ms]0x2318--3

Toffset [°C] = 175 * word[0] / 216

1

Response parameter: Offset temperature

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

3.6.3

set_sensor_altitude
Description: Reading and writing of 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 setting (see chapter 3.9.1) commandmust be issued. Per default, the sensor altitude is set to 0 meter above sea-level.
Table 15: set_sensor_altitude I2C sequence description
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.a.s.l.
Write

0x24270x079e0x09(hexadecimal)

CommandSensor altitude = 1’950 m

CRC of 0x79e

3.6.4

get_sensor_altitude

Table 16: get_sensor_altitude I2C sequence description
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.a.s.l.
Write

0x2322(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x044c0x42(hexadecimal)

Sensor altitude = 1’100 m

CRC of 0x044c

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3.6.5

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 using set_ambient_pressure overrides any pressure compensation basedon a previously set sensor altitude.
Table 17: set_ambient_pressure I2C sequence description
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

3.7 Field Calibration
To realize high initial and long-term accuracy, the SCD4x includes two field calibration features. Forced recalibration (FRC)
enables restoring highest accuracy with the assistance of a CO 2 reference value immediately. Typically, FRC is applied tocompensate for drifts originating from the sensor assembly process or other extensive stresses. Automatic self-calibration (ASC)ensures highest long-term stability of the SCD4x without the need of manual action steps from the user. The automatic selfcalibration algorithm assumes that the sensor is exposed to the atmospheric CO 2 concentration of 400 ppm at least once per
week.

3.7.1

perform_forced_recalibration

Description: To successfully conduct an accurate forced recalibration, the following steps need to be carried out:
1. Operate the SCD4x in the operation mode later used in normal sensor operation (periodic measurement, low power
periodic measurement or single shot) for > 3 minutes in an environment with homogenous and constant CO2
concentration.
2. Issue stop_periodic_measurement. Wait 500 ms for the stop command to complete.
3. Subsequently issue the perform_forced_recalibration command and optionally read out the FRC correction (i.e. themagnitude of the correction) after waiting for 400 ms for the command to complete.
• A return value of 0xffff indicates that the forced recalibration has failed.
Note that the sensor will fail to perform a forced recalibration if it was not operated before sending the command. Please makesure that the sensor is operated at the voltage desired for the application when applying the forced recalibration sequence.

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Table 18: perform_forced_recalibration I2C sequence description
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 490 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

3.7.2

set_automatic_self_calibration_enabled
Description: Set the current state (enabled / disabled) of the automatic self-calibration. By default, ASC is enabled. To save thesetting to the EEPROM, the persist_setting (see chapter 3.9.1) command must be issued.
Table 19: set_automatic_self_calibration_enabled I2C sequence description.
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 automatic self-calibration status: enabledWrite

0x24160x00010xB0(hexadecimal)

CommandASC enabled

CRC of 0x0001

3.7.3

get_automatic_self_calibration_enabled

Table 20: get_automatic_self_calibration_enabled I2C sequence description
Write(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 automatic self-calibration status: disabled
Write

0x2313(hexadecimal)

Command

Wait

1 ms

command execution time

Response

0x00000x81(hexadecimal)

ASC disabled

CRC of 0x0000

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3.8 Low Power operation
To enable use-cases with a constrained power-budget, the SCD4x features a low power periodic measurement mode with signal
update interval of approximately 30 seconds. While the low power mode saves power and reduces self-heating of the sensor,
the low power periodic measurement mode has a longer response time.
The low power periodic measurement mode is initiated and read-out in a similar manner as the default periodic measurement.
Please consult chapter 3.5.2 for further instructions. To avoid receiving a NACK in case the result of a subsequent measurement
is not ready yet, the get_data_ready_status command can be used to check whether new measurement data is available forread-out.

3.8.1

start_low_power_periodic_measurement

Description: start low power periodic measurement, signal update interval is approximately 30 seconds.
Table 21: start_low_power_periodic_measurement I2C sequence description
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)

Command3.8.2

get_data_ready_status

Table 22: get_data_ready_status I2C sequence description

Write(hexadecimal)
0xe4b8Input parameter: -Response parameter: data ready status

length [bytes]

signal conversion

length[bytes]--3

signal conversion
If the least significant 11 bits ofword[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

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command execution time

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3.9 Advanced Features
3.9.1

persist_settings

Description: Configuration settings such as the temperature offset, sensor altitude and the ASC enabled/disabled parameterare by default stored in the volatile memory (RAM) only and will be lost after a power-cycle. The persist_settings commandstores the current configuration in the EEPROM of the SCD4x, making them persistent across power-cycling. To avoid
unnecessary wear of the EEPROM, the persist_settings command should only be sent when persistence is required and if actualchanges to the configuration have been made. The EEPROM is guaranteed to endure at least 2000 write cycles before failure.
Note that field calibration history (i.e. FRC and ASC, see chapter 3.7) is automatically stored in a separate EEPROM
dimensioned for the specified sensor lifetime.
Table 23: persist_settings I2C sequence description
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)

Command3.9.2

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 (big endian format).
Table 24: get_serial_number I2C sequence description
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]1

Max. command
duration [ms]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

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3.9.3

perform_self_test

Description: The perform_self_test feature can be used as an end-of-line test to check sensor functionality and the customer
power supply to the sensor.
Table 25: perform_self_test I2C sequence description
Write(hexadecimal)

Input parameter: -Response parameter: sensor status

length [bytes]

signal conversion

length [bytes]

signal conversion

0x3639--3

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

Max. command
duration [ms]10000

Example: perform self-test, no malfunction detected
Write

0x3639(hexadecimal)

Command

Wait

10000 ms

Response

0x00000x81(hexadecimal)

No malfunction detected

CRC of 0x0000

3.9.4

command execution time

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.
Table 26: perform_factory_reset I2C sequence description
Write(hexadecimal)

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

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x3632

-

-

-

-

1200

Example: perform factory reset
Write

0x3632(hexadecimal)

Command3.9.5

reinitDescription: The reinit command reinitializes the sensor by reloading user settings from EEPROM. Before sending the reinitcommand, the stop measurement command must be issued. If the reinit command does not trigger the desired re-initialization,a power-cycle should be applied to the SCD4x.
Table 27: reinit I2C sequence description
Write(hexadecimal)

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

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x3646

-

-

-

-

20

Example: reinit
Write

0x3646(hexadecimal)

Command re-initializationwww.sensirion.com

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3.10 Low power single shot (SCD41)
In addition to periodic measurement modes, the SCD41 features a single shot measurement mode, i.e. allows for on-demandmeasurements.
The typical communication sequence is as follows:
1. The sensor is powered up.
2. The I2C master sends a single shot command and waits for the indicated max. command duration time.
3. The I2C master reads out data with the read measurement sequence (chapter 3.5.2).
4. Steps 2-3 are repeated as required by the application.
To reduce noise levels, the I2C master can perform several single shot measurements in a row and average the CO2 output
values. After a power cycle, the initial two single shot readings should be discarded to maximize accuracy. The idle current in
between measurements is 0.15 mA (typ.), respectively 0.2 mA (max.). The energy consumed per single shot typically is 243 mJ(296 mJ max.).
As for the periodic measurement modes, the automatic self-calibration (ASC) is enabled per default in single shot operation.
The automatic self-calibration is optimized for single shot measurements performed every 5 minutes. Longer measurement
intervals will result in less frequent self-calibration sequences. Note that no self-calibration is issued if the sensor is power-cycled
between single shot measurements Please consult Chapter 3.7 for a detailed description of the automatic-self calibration andthe corresponding commands.

3.10.1 measure_single_shot
Description: On-demand measurement of CO2 concentration, relative humidity and temperature. The sensor output is readusing the read_measurement command (chapter 3.5.2).
Table 28: measure_single_shot I2C sequence description
Write(hexadecimal)

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

signal conversion

length [bytes]

signal conversion

Max. command
duration [ms]0x219d

-

-

-

-

5000

Example: measure single shot
Write

0x219d(hexadecimal)

Command3.10.2 measure_single_shot_rht_only
Description: On-demand measurement of relative humidity and temperature only. The sensor output is read using theread_measurement command (chapter 3.5.2). CO2 output is returned as 0 ppm.
Table 29: measure_single_shot_rht_only I2C sequence description
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)

Commandwww.sensirion.com

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3.11 Checksum Calculation
The 8-bit CRC checksum transmitted after each data word is generated by a CRC algorithm. Its properties are displayed inTable 30. 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 30 I2C CRC properties.

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4

Mechanical specifications

4.1 Package Outline
Figure 3 schematically displays the package outline. The notched corner of the protection membrane serves as a polarity
mark to indicate pin 1 location. Nominal dimensions and tolerances are listed in Table 31.

Figure 3: Packaging outline drawing of the SCD4x: (left) top view and (right) side view. Nominal
dimensions and tolerances are listed in millimeters.

Dimension

a

b

c

d

e

f

Nominal [mm]Tolerance [mm]

10.1
± 0.3

10.1
± 0.3

8.5
± 0.2

7.8
± 0.2

5.5
± 0.3

0.8
± 0.2

Table 31: Nominal dimensions and tolerances SCD4x (all in mm). The weight of the sensor is approx.
0.6 g.

Note that the white protection membrane on top of the sensor must not be removed or tampered with to ensure proper sensor
operation.

4.2 Land Pattern
Recommended land pattern, solder paste and solder mask are shown in Figure 4. These are recommendations only and not
specifications. The exact mask geometries, distances and stencil thicknesses must be adapted to the customer soldering
processes.

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

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4.3 Tape & Reel Package

Figure 5: Technical drawing of the packaging tape with sensor orientation in tape. Header tape is to
the right and trailer tape to the left on this drawing. Dimensions are given in millimeters.

4.4 Moisture Sensitivity Level
Sensirion SCD4x sensors shall be treated according to Moisture Sensitivity Level 3 (MSL3) as described in IPC/JEDEC J-STD033B1. Exposure to moisture levels or solder reflow temperatures, which exceed the limits as stated in this document, can resultin yield loss and reliability degradation.
The manufacturing floor time (out of bag) at the customer’s end is 168 hours at normal factory conditions (≤30°C and 60%RH).
If sensors are not mounted within this time, or have been exposed to higher temperatures and humidity (>30°C and >60%RH),
or there is any doubt about the airtight integrity of the dry pack, the parts should be baked (baking parameters see Table 32).
The maximum allowed baking temperature is 40°C if the sensors are inside the reel.
Table 32: Baking condition SCD4x if floor time (168 h) with open bag is exceeded.
SCD4x package type

Baking temperature

Min. baking time

Baking condition

Sensors removed from tape

90 °C

48 hours

RH < 5 %Sensors in tape

40 °C

23 days

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4.5 Soldering Instructions
For soldering, standard reflow soldering ovens may be used. The sensors are designed to withstand soldering profile according
to IPC/JEDEC J-STD-020 with a maximum peak temperature of 235°C during up to 30 sec for Pb-free assembly in IR/Convection
reflow ovens.
Note that due to the comparably large size of the SCD4x sensor significant temperature differences across the sensor element
can occur 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 235° C is notexceeded at any time in any part of the sensor.
Do not apply any board wash process step subsequently to the reflow soldering. Note that the dust cover on top of the cap mustnot be removed or wetted with any liquid. Finally, the SCD4x is not compatible with vapor phase reflow soldering.
Average ramp-up rate

< 3 °C / second

Liquid phase
▪ TL
▪ tL

< 220 °C
< 60 seconds

Peak temperature
▪ TP
▪ tP

≤ 235 °C
< 30 seconds

Ramp-down rate

< 4 °C / seconds fortemperature > T L

Table 33 Soldering profile parameter

4.6 Traceability
All SCD4x sensors have a distinct electronic serial number for identification and traceability (see chapter 3.9.2). The serial
number can be decoded by Sensirion only and allows for tracking through production, calibration, and testing.

5

Ordering Information

Use the part names and product numbers shown in the following table when ordering the SCD4x CO2 sensor. For
the latest product information and local distributors, visit http://www.sensirion.com/.
Part Name
SCD40-D-R2
SCD40-D-R1
SCD41-D-R2
SCD41-D-R1
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)
600 sensors per reel60 sensors per reel
600 sensors per reel60 sensors per reel
1

Product Number
3.000.521
3.000.496
3.000.498
3.000.497
3.000.455

1

3.000.124

Table 34 SCD4x ordering options

6

Revision History
Date
January 2021
April 2021

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Version1
1.1

Page(s)all
16 - 17

Changes
Initial release
Adjustment max. command time self-test (chapter 3.9) and single shot (chapter
3.10), minor revisions on other pages

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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, hand ling, 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 wit h 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.
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 an d 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 © 2021, by SENSIRION. CMOSens® is a trademark 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 3 3444 4940
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 3 5506701
info@sensirion.com
www.sensirion.com

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

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