SCD4x Low Power Operation
Sensirion’s SCD4x product family enables cost efficient CO2 measurement at high accuracy within a tiny form
factor. For many of its applications, optimizing power consumption is a key requirement. To help achieve this,
SCD4x sensors feature a range of high-performance and low power operation modes. This guide is intended tohelp you find and operate the SCD4x at the optimal trade-off point between sensor performance and energy
efficiency as based on your application’s needs. It provides an overview of the sensor’s measurement modes, theirfeatures and the sensor’s typical power consumption in each mode.

1 The Power-Performance Trade-Off
Performing a CO2 measurement is the most significant part ofthe power consumption of the SCD4x. Consequently,
adapting the sampling period is the simplest and mosteffective way to optimize sensor’s power consumption.
However, increasing the sampling period comes at the costof also increasing the response time to external changes in
CO2 concentration, as more time passes before the sensor
provides a new data point. Furthermore, taking fewer
measurements over time also increases the noise level
observed in the output signal. This occurs because higher
sampling periods generally decrease the feasibility of filteringor averaging over several data points to alleviate signal noise.
The resulting trade-off between power consumption andsensing performance needs to be considered carefully to best
meet all requirements set forth by the intended application.

Low power consumption

High signal update rate
/ Fast response time

Low repeatability/ Low noise level

Figure 1: The three-way trade-off to bemastered for low power applications

2 Operation Modes
SCD4x CO2 sensors feature up to four different operation modes with different features and capabilities: two periodic
measurement modes and two single shot modes. An overview of the typical average supply current required by thesensor at different sampling periods and 3.3 V is provided in Table 1 below.
Measurement mode

Sampling Period
5 sec

Typical average supply
current at 3.3 V
15 mA

Typical average supply
current at 5 V
11 mA

High performance modeLow power mode

30 sec

3.2 mA

2.8 mA

Idle single shot mode60 sec (1 min)

1.5 mA

1.1 mA

300 sec (5 min)450 µA360 µA

600 sec (10 min)

250 µA180 µA

1200 sec (20 min)

130 µA

90 µA

3600 sec (1 h)

43 µA

30 µA

Power-cycled single shot mode

Table 1: Overview of typical average supply current by operation modede and sampling period at 3.3 V

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2.1 High-Performance Mode
This mode represents the standard periodic measurement mode for SCD4x sensors as initiated using thestart_periodic_measurement command detailed in section 3.5 of the SCD4x datasheet. It features a fixed update
interval of 5 seconds and is the recommended operation mode for applications requiring relatively fast response times
and detailed knowledge of the evolution of the CO2 concentration over time. Automatic Self Calibration (ASC) is
activated by default in this measurement mode to ensure long-term sensor accuracy. Note that this is the only available
operation mode for SCD42.

2.2 Low Power Mode
Low power mode operation allows for measurement of the ambient CO2 concentration with a longer, fixed sampling
period of 30 seconds. This reduces the average power consumption of the sensor by more than 80% as compared tohigh-performance mode operation. It is initiated using the start_low_power_periodic_measurement command detailed
in section 3.8 of the datasheet. ASC is featured and activated by default also in this measurement mode.

2.3 Idle Single Shot Operation (SCD41 only)
For idle single shot operation, the SCD41 performs individual measurements only on-demand using themeasure_single_shot command detailed in section 3.10 of the datasheet. Thus, the energy required for taking a CO2
reading is consumed only when a measurement is needed, allowing for significant reductions in the average power
consumption of the sensor as compared to the periodic measurement modes. In between measurements, the sensor
remains powered-up and in the idle state. This enables flexible adjustment of the sampling period to the sensing
requirements of the application.
ASC is available and enabled by default for idle single shot operation. However, it is recommended to adjust thesensor’s standard ASC period parameter depending on the average sampling period achieved during idle single shotoperation. Please consult section 5.2 of this document for details.

2.4 Power Cycled Single Shot Operation (SCD41 only)
The sensor is powered down between single shot measurements in this mode, which eliminates the idle power
consumption of the sensor. This can be achieved either by cutting and later re-applying the supply voltage to thesensor or by using the power_down / wake_up commands described in Table 2 below and in section 3.10 of thedatasheet. Single shot measurements are requested using the measure_single_shot command just as in idle singleshot operation.
CommandHex. Code

Sequence typeMax. command duration [ms]power_down

0x36e0write

1

wake_up

0x36f6write

20

Table 2: Commands for Power Cycling

Because the sensor requires one single shot measurement to stabilize after power cycling, the CO2 reading of theinitial single shot after startup should always be discarded. This makes power cycled single shot operation preferable
to idle single shot operation only when the average sampling period is above 380 seconds.
Note: ASC is not supported for power cycled single shot operation.

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3 Typical Power Consumption
Figure 2 provides an overview of the average power consumption that can be expected from SCD4x sensors at a
supply voltage of 3.3 V, depending on the operation mode and the sampling period. The included data markers
visualize the sampling periods provided as examples in Table 1. Note that whether ASC is enabled does not influence
the sensor’s power consumption.

Average Current Consumption in [mA]

1001010.1

0.01
1

10100

1000

10000

Sampling Period [s]High Performance ModeLow Power ModeIdle Single Shot Mode

Power-Cycled Single Shot Mode

Figure 2: Typical Average Current Consumption by Operation Mode and Sampling Period at 3.3 V
On short timescales, the power consumption profile of SCD4x is characterized by two phases: Sensor data acquisition
and idle operation. During data acquisition, the sensor exhibits a pulsed current profile that may reach the sensors
specified peak supply current. During the idle phase between samples, the required current returns to less than 200µA. Figure 3 provides a schematic illustration of this characteristic. The sensor’s power supply should be designedwith respect to the peak current and maximum peak-to-peak voltage ripple (without the sensor) as specified in thedatasheet.

Figure 3: Schematic illustration of the current profile of SCD4x sensors

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3.1 High Performance & Low Power Mode
The average current consumption that can be expected from the sensor during continuous measurement in either
high-performance or low power mode is detailed in Table 3 below.
Parameter

Symbol Conditions
VDD = 3.3 VVDD = 5 V
IDD
VDD = 3.3 V
VDD = 5 V

Average current consumption for periodic
measurement in high-performance mode
Average current consumption for periodic
measurement in low power modeMin.

Typical
15
11
3.2
2.8

Max.
18
13
3.5
3UnitsmA
mA
mA
mA

Table 3: Average current consumption during operation in continuous measurement modes

3.2 Idle Single Shot Mode
As measurements are only taken on demand in idle single shot mode, the current consumption of the sensor varies
depending on the resulting average sampling period. The average current consumption that can typically be expectedfrom the SCD4x in idle single shot mode can be calculated using Equation 1:𝐼𝑎𝑣𝑔 = 𝐼𝑖 +𝑞𝑠𝑠
𝑇𝑠𝐼𝑎𝑣𝑔𝑇𝑠𝐼𝑖𝑞𝑠𝑠

Average power consumption [mA]
Average sampling period [s]0.20 mA , Vdd = 3.3 V
Idle current {0.17 mA , Vdd = 5 V
77 mC , Vdd = 3.3 V
Additional charge per idle single shot {54 mC , Vdd = 5 V

Equation 1: Typical average current consumption in idle single shot mode

3.3 Power Cycled Single Shot Mode
If the sensor is powered up to obtain only one single useful CO2 reading at a time, the typical average current
consumption can be obtained using Equation 2. Note that the following formula assumes performing the useful single
shot measurement immediately following the initial discarded single shot required for sensor stabilization.
𝑞𝑝𝑐𝑠𝑠
𝐼𝑎𝑣𝑔 =𝑇𝑢𝐼𝑎𝑣𝑔
𝑇𝑢Average current [mA]
Average useful sampling period [s]𝑞𝑝𝑐𝑠𝑠

Total charge per useful single shot {154 mC , Vdd = 3.3 V
108 mC , Vdd = 5 V

Equation 2: Typical average current consumption in power cycled single shot modewww.sensirion.com

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4 Typical Command Sequences
The following figures provide a flowchart overview of typical command sequences for operating SCD4x in each of its
operation modes. For detailed descriptions of all available I2C commands and their implementation, please consult
section 3 of the sensor datasheet. Please also see our online collection of sample code and drivers for SCD4x toaccelerate your prototyping and development.

4.1 High Performance Mode

Figure 4: Command Flowchart for High Performance Mode Operation

4.2 Low Power ModeFigure 5: Command Flowchart for Low Power Mode Operation

4.3 Idle Single Shot Mode (SCD41 only)

Figure 6: Command Flowchart for Idle Single Shot Mode Operation

4.4 Power Cycled Single Shot Mode (SCD41 only)

Figure 7: Command Flowchart for Power-Cycled Single Shot Mode Operationwww.sensirion.com

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5 Field Calibration for Low Power Operation Modes
5.1 Performing Forced Recalibration (FRC):
FRC enables quickly restoring highest baseline accuracy with the assistance of a CO2 reference value. Typically, FRC
is applied to compensate for drifts originating from the sensor assembly process or other extensive stresses. Before
applying the perform_forced_calibration command detailed in section 3.7.1 of the datasheet, the sensor is to be runfor > 3 minutes using the operation mode and sampling rate intended for field use in an environment with known,homogeneous, and constant CO2 concentration and at the same supply voltage used in the field.
For idle single shot mode, if the average sampling period intended for field use is more than or equal to 60 seconds,
the run-up to performing FRC is to be done for 5 minutes at a sampling period of 1 minute. The same procedure also
applies to performing FRC if the sensor is to be operated in power-cycled single shot mode in the field.

5.2 Optimizing ASC for Idle Single Shot Mode Operation
For idle single shot mode, ASC will default to self-calibration periods optimized for an average sampling rate of 5
minutes. If the average sampling period deviates significantly from this, it is recommended to adjust the initial andstandard ASC period parameters onboard the sensor.
The initial period represents the number of readings after powering up the sensor for the very first time to trigger thefirst automatic self-calibration. The standard period represents the number of subsequent readings periodicallytriggering ASC after completion of the initial period. Sensirion recommends adjusting the number of samples
comprising initial and standard period to 2 and 7 days at the average intended sampling rate, respectively.
The number of single shots for initial and standard period can be adjusted onboard the sensor using the commands
detailed in Table 4 below. Note that the parameter value represents twelve times the number of single shots defining
the length of either period. Furthermore, this parameter must be an integer and a multiple of four.
Example: Average sampling rate: 3 minutes
Standard period: 7 days = 3360 single shots → Standard period parameter value = 280
Initial period: 2 days = 960 single shots → Initial period parameter value = 80
To save changes to ASC parameters to non-volatile memory, the persist_settings command detailed in section 3.9.1of the datasheet is required. The history of readings needed for performing ASC is automatically stored to non-volatilememory after each complete batch of 48 idle single shots was performed without power cycling in between.
CommandHex.
CodeSequence
type

Parameter
length incl.
CRC [bytes]

Response
length incl.
CRC [bytes]

Max.
commandduration [ms]get_automatic_self_calibration_initial_period

0x2340

read-

3

1

set_automatic_self_calibration_initial_period

0x2445

write

3

-

1

get_automatic_self_calibration_standard_period

0x234b

read-

3

1

set_automatic_self_calibration_standard_period

0x244e

write

3-

1

Table 4: Commands for Adjusting ASC Period Durationwww.sensirion.com

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Disclaimer
This document is meant as a guideline and cannot be considered as complete. It is subject to changes without prior notice.

Revision History
Date
July 2022

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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 resultin 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 andhold harmless SENSIRION and its officers, employees, subsidiaries, affiliates and distributors against all claims, costs, damages andexpenses, 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/ordegradation, take customary and statutory ESD precautions when handling this product. See application note “ESD, Latchup and EMC” formore 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 thisproduct shall be of the quality, material and workmanship defined in SENSIRION’s published specifications of the product. Within suchperiod, 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, orworkmanship;•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 useof 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 dovary 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

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