SCD4x
Breaking the size barrier in CO2 sensing
Features
▪ Photoacoustic NDIR 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 NDIR
sensing principle and Sensirion’s patented PASens® and
CMOSens® 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.
CO2 is a key indicator for indoor air quality as high levels
compromise humans’ cognitive performance and wellbeing. The SCD4x enables smart ventilation systems to
regulate ventilation in the most energy-efficient and
human-friendly way. Moreover, indoor air quality monitors
and other connected devices based on the SCD4x can
help maintaining low CO2 concentration for a healthy,
productive environment.
Functional Block Diagram
Device 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, single shot
mode supported
SCD42-D-R2 Separate datasheet, see
https://sensirion.com/products/cat
alog/SCD42/
Full product list on page 22
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Table of Contents
1
2
3
4
5
6
Sensor Performance ......................................................................................................................................... 3
1.1
CO2 Sensing Performance .......................................................................................................................... 3
1.2
Humidity Sensing Performance ................................................................................................................... 3
1.3
Temperature Sensing Performance5 ........................................................................................................... 3
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
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 ............................................................................................................................... 19
Mechanical specifications .............................................................................................................................. 20
4.1
Package Outline ........................................................................................................................................ 20
4.2
Land Pattern .............................................................................................................................................. 20
4.3
Tape & Reel Package................................................................................................................................ 21
4.4
Moisture Sensitivity Level .......................................................................................................................... 21
4.5
Soldering Instructions ................................................................................................................................ 22
4.6
Traceability ................................................................................................................................................ 22
Ordering Information....................................................................................................................................... 22
Revision History ................................................................................................................................................ 23
ESD Precautions ................................................................................................................................................. 24
Warranty .............................................................................................................................................................. 24
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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
Additional accuracy drift per year with
automatic self-calibration algorithm
enabled4
Conditions
400 ppm – 2’000 ppm
400 ppm – 5’000 ppm
Typical
τ63%, typical
Value
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
Typical
τ63%, 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 and shipping reduce the accuracy of the sensor.
Sensor assembly temporarily reduces sensor accuracy. Accuracy is fully restored with FRC or ASC recalibration features > 5 days after sensor assembly. Accuracy is based
on tests with gas mixtures having a tolerance 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 must be exposed to air with CO2 concentration 400 ppm regularly. Maximum accuracy drift per year estimated
from 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, the
temperature-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 DC6
Voltage ripple peak to peak
Peak supply current7
Average supply current for periodic
measurement
Average supply current for low power periodic
measurement
Average supply current for periodic single shot
measurement, 1 measurement / 5 minutes
(SCD41 only)8
Input high level voltage
Input low level voltage
Output low level voltage
Symbol Conditions
VDD
VRPP
VDD = 3.3 V
Ipeak
VDD = 5 V
VDD = 3.3 V
IDD
VDD = 5 V
VDD = 3.3 V
IDD
VDD = 5 V
VDD = 3.3 V
IDD
VDD = 5 V
Min.
2.4
Typical
3.3 or 5.0
VIH
VIL
VOL
0.65 x VDD
175
115
15
11
3.2
2.8
0.45
0.36
3 mA sink current
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 conditions9
MSL Level
DC supply voltage
Max voltage on pins SDA, SCL, GND
Input current on pins SDA, SCL, GND
Short term storage temperature10
Recommended storage temperature
ESD HBM
ESD CDM
Maintenance Interval
Sensor lifetime12
Conditions
Non-condensing
Maintenance free when ASC fieldcalibration algorithm11 is used.
Typical operating conditions
Value
-10 – 60°C
0 – 95 %RH
3
- 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
Supply voltage must be kept stable during sensor operation
Power supply should be designed with respect to peak current.
8 On-demand measurement with freely adjustable interval. See chapter 3.10
9 Accuracy can be reduced at relative humidity levels lower than 10 %.
10 Short term storage refers to temporary conditions during e.g. transport.
11 For proper function of ASC field-calibration algorithm the SCD4x has to be exposed to clean air with 400 ppm CO2 concentration regularly.
12 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 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. should both be connected to
the same power supply. The combined maximum current drawn on VDD and VDDH is indicated in Table 4. Care should be
taken 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 I 2C manual13
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 details13). 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.
13
NXP’s I2C-bus specification and user manual UM10204, Rev.6, 4 April 2014
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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 13).
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. Code
I2 C
0x62
address
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 threshold
voltage, the sensor needs 1000 ms to enter the idle state. Once the idle state is entered 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 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 the
checksum (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 is
required 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 found
further down. *Column indicates whether command can be executed while a periodic measurement
is running.
Domain
Basic 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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Hex.
Code
I2C sequence type
(see chapter 3.3)
Execution
time
[ms]
During
meas.*
start_periodic_measurement
0x21b1
send command
-
no
read_measurement
0xec05
read
1
yes
stop_periodic_measurement
0x3f86
send 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
0x362f
send command and
fetch 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
0x21ac
send command
-
no
get_data_ready_status
0xe4b8
read
1
yes
persist_settings
0x3615
send 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
reinit
0x3646
send command
20
no
measure_single_shot
0x219d
send command
5000
no
measure_single_shot_rht_only
0x2196
send command
50
no
power_down
0x36e0
send command
1
no
wake_up
0x36f6
send command
20
no
Command
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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)
Command
3.5.2
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, the
get_data_ready_status can be issued to check data status (see chapter 3.8.2 for further details). The I2C master can abort the
read 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 ∗
3
RH = 100 ∗
word[1]
216 −1
Max.
command
duration [ms]
1
word[2]
216 −1
Example: read sensor output (500 ppm, 25 °C, 37 % RH)
Write
0xec05
(hexadecimal)
Command
Wait
1 ms
Response
0x01f4
0x7b
0x6667
0xa2
0x5eb9
0x3c
(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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3.5.3
stop_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 the
pressure or altitude enables highest accuracy of the CO2 output signal across a large pressure range. Setting the temperature
offset 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 (see
chapter 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 SCD4x
inside 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 typical
operation conditions (including the operation mode to be used in the application) and in thermal equilibrium. Per default, the
temperature 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 I2C sequence description
Write
(hexadecimal)
Input parameter: Offset temperature
Response parameter: -
length [bytes]
signal conversion
length [bytes]
signal conversion
Max. command
duration [ms]
0x241d
3
word[0] = Toffset [°C] * 216 / 175
-
-
1
Example: set temperature offset to 5.4 °C
Write
0x241d
0x07e6
0x48
(hexadecimal)
Command
Toffset = 5.4 °C
CRC of 0x7e6
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3.6.2
get_temperature_offset
Table 14: get_temperature_offset I2C sequence description
Write
(hexadecimal)
Input parameter: length [bytes]
signal conversion
length [bytes]
signal conversion
Max.
command
duration [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
0x0912
0x63
(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) command
must 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
0x2427
0x079e
0x09
(hexadecimal)
Command
Sensor 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 altitude
length [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
0x044c
0x42
(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 pressure
compensation. Note that setting an ambient pressure using set_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 to ensure sensor accuracy.
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]
0xe000
3
word[0] = ambient P [Pa] /
100
-
-
1
Example: set ambient pressure to 98’700 Pa
Write
0xe000
0x03db
0x42
(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 CO2 reference value immediately. Typically, FRC is applied to
compensate 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 CO2 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. the
magnitude 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 make
sure 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
0x362f
3
word[0] = Target
concentration [ppm CO2]
3
FRC correction [ppm CO2] =
word[0] – 0x8000
Max.
command
duration [ms]
400
word[0] = 0xffff in case of
failed FRC
Example: perform forced recalibration, reference CO2 concentration is 480 ppm
Write
0x362f
0x01e0
0xb4
(hexadecimal)
Command
Input: 480 ppm
CRC of 0x01e0
Wait
400 ms
command execution time
Response
0x7fce
0x7b
(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 the
setting 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 enabled
word[0] = 0 → ASC disabled
-
-
1
Example: set automatic self-calibration status: enabled
Write
0x2416
0x0001
0xB0
(hexadecimal)
Command
ASC 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 enabled
word[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
0x0000
0x81
(hexadecimal)
ASC disabled
CRC of 0x0000
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Version 1.3 – September 2022
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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 for
read-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)
Command
3.8.2
get_data_ready_status
Table 22: get_data_ready_status I2C sequence description
Write
(hexadecimal)
0xe4b8
Input parameter: -
Response parameter: data ready status
length [bytes]
signal conversion
length
[bytes]
-
-
3
signal conversion
If the least significant 11 bits of
word[0] are 0 → data not ready
else → data ready for read-out
Max. command
duration [ms]
1
Example: read data ready status: data not ready
Write
0xe4b8
(hexadecimal)
Command
Wait
1 ms
Response
0x8000
0xa2
(hexadecimal)
Least significant 11 bits are 0 → data not ready
CRC of 0x8000
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command execution time
Version 1.3 – September 2022
14/24
3.9 Advanced Features
3.9.1
persist_settings
Description: Configuration settings such as the temperature offset, sensor altitude and the ASC enabled/disabled parameter
are by default stored in the volatile memory (RAM) only and will be lost after a power-cycle. The persist_settings command
stores 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 actual
changes 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)
Command
3.9.2
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] 220 °C
< 60 seconds
Peak temperature
▪ TP
▪ tP
≤ 235 °C
< 30 seconds
Ramp-down rate
< 4 °C / seconds for
temperature > TL
Table 35 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 to
computer
Ordering quantity (pcs)
600 sensors per reel
60 sensors per reel
600 sensors per reel
60 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 36 SCD4x ordering options
www.sensirion.com
Version 1.3 – September 2022
22/24
6
Revision History
Date
January 2021
April 2021
Version
1
1.1
Page(s)
all
16 - 17
May 2022
1.2
September 2022
1.3
3
12
18
22
all
All
www.sensirion.com
Changes
Initial release
Adjustment max. command time self-test (chapter 3.9) and single shot (chapter
3.10), minor revisions on other pages
Clarification on additional sensor accuracy drift (Table 1)
Clarification of set_ambient_pressure command description (chapter 3.6.5)
Addition of power_down and wake_up commands (chapter 3.10)
Addition of minor temporary accuracy deviation after reflow soldering (chapter 4.5)
Minor editorial revisions
Minor editorial revisions
Version 1.3 – September 2022
23/24
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 in
personal injury. Do not use this product for applications other than its intended and authorized use. Before installing, handling, using or
servicing this product, please consult the data sheet and application notes. Failure to comply with these instructions could result in
death or serious injury.
If the Buyer shall purchase or use SENSIRION products for any unintended or unauthorized application, Buyer shall defend, indemnify and hold
harmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages and expenses, and
reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized
use, 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 product
shall 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 the
goods. SENSIRION explicitly disclaims all warranties, express or implied, for any period during which the goods are operated or stored not in
accordance 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) to
improve reliability, functions and design of this product.
Copyright © 2022, by SENSIRION. CMOSens® is a trademark of Sensirion. All rights reserved
Headquarters and Subsidiaries
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Sensirion Inc., USA
phone: +1 312 690 5858
info-us@sensirion.com
www.sensirion.com
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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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