STC31-R3

Datasheet STC31 CO2 Sensor Based on Thermal Conductivity  Calibrated gas concentration and temperature output  Next level repeatability and long term stability  Compensates for Relative Humidity with additional SHTxx sensor Product Summary The STC3x sensor family is Sensirion’s series of Gas Concentration sensors designed for high-volume applications. The STC3x utilizes a revolutionized thermal conductivity measurement principle, which results in superior repeatability and long-term stability. This make the STC31 a perfect choice for applications where reliability is key. The sensor features a digital I2C interface, which makes it easy to connect directly to a microprocessor. The outstanding performance of these sensors is based on Sensirion’s patented CMOSens® sensor technology, which combines the sensor element, signal processing and digital calibration on a small CMOS chip. The well-proven CMOS technology is perfectly suited for high-quality mass production and is the ideal choice for demanding and cost-sensitive OEM applications. Benefits of Sensirion’s CMOSens® Technology      High reliability and long-term stability Best signal-to-noise ratio Industry-proven technology with a track record of more than 15 years Designed for mass production High process capability Content 1. Sensor Performance .............................................................. 2 2. Specifications ......................................................................... 3 3. Digital Interface Description ................................................... 4 4. Physical specifications ......................................................... 12 5. Sensor Integration................................................................ 14 6. Shipping Package ................................................................ 15 7. Ordering Information ............................................................ 15 Important Notices ......................................................................... 16 Headquarters and Subsidiaries .................................................... 16 www.sensirion.com – Confidential D1 Version 1.1 – October 2020 1/16 1. Sensor Performance 1.1 Concentration1 Parameter Calibrated for2 Measurement range4 Accuracy5 Repeatability Temperature stability6 Resolution 1.2 Value CO2 in N2 and CO2 in air3 0 to 25 vol% 0.5 vol% + 3% measured value 0 to 100 vol% 1 vol% + 3% measured value 0.2 vol% 0.025 vol% / °C 16 bit Temperature 7 Parameter Measurement range Resolution Accuracy Repeatability Value -20 °C to 85 °C 16 bit 0.5 °C (10 °C to 50 °C) 1.5 °C (-20 °C to 85 °C) 0.1°C 1 Valid at temperature at which ASC or FRC is performed and humidity = 0-95% RH, 12.5°C 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 [°𝐶] = 3.5.3 Relative Humidity The relative humidity value written to the sensor is an unsigned integer number. The integer value can be converted to the physical value by the following conversion formula. 𝑆𝑇𝐶3𝑥 𝑖𝑛𝑝𝑢𝑡 × 100 216 − 1 Example: 65535 => 100% relative humidity 𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝐻𝑢𝑚𝑖𝑑𝑖𝑡𝑦 [%] = 3.5.4 Pressure The pressure value written to the sensor is an unsigned integer number. The integer value can be converted to the physical value by the following conversion formula. 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 [𝑚𝑏𝑎𝑟] = 𝑆𝑇𝐶3𝑥 𝑖𝑛𝑝𝑢𝑡 Example 1023 => 1023 mbar www.sensirion.com – Confidential D1 Version 1.1 – October 2020 11/16 4. Physical specifications 4.1 Package outline Figure 1 Dimensional drawing of STC3x including package tolerances (units mm) 4.2 Land pattern The land pattern is recommended to be designed according to the used PCB and soldering process together with the physical outer dimension of the sensor. 4.3 Pin assignment The pin assignments of the STC31 can be found in Table 1. Pin no. Name Description 1 VSS Connect to ground 2 Reserved. Do not connect 3 ADDR I2C Address Selection 4 SCL Serial Clock (I2C Interface) 5 VSS Connect to ground 6 VDD VDD Supply 7 SDA Bidirectional Serial Data (I2C Interface) 8 Reserved. Do not connect 9 VSS Connect to ground 10 Reserved. Do not connect 11 VSS Connect to ground 12 Reserved. Do not connect Table 1: STC31 pin assignment (bottom view). 4.3.1 Power Pins (VDD, GND) The power supply pins must be decoupled with a 100 nF capacitor that shall be placed as close to the sensor as possible. www.sensirion.com – Confidential D1 Version 1.1 – October 2020 12/16 4.3.2 Serial Clock and Serial Data (SCL, SDA) The SCL and SDA are bidirectional pins of the I2C slave interface. The SCL is the Serial Clock pin and the SDA is the Serial Data pin. For more details about the I2C interface refer to section 3. Both SCL and SDA lines are open-drain I/Os with diodes to VDD und VSS. They should be connected to external pull-up resistors (please refer to Figure 2). A device on the I2C bus must only drive a line to ground. The external pull-up resistors (e.g. Rp = 10 kΩ) are required to pull the signal high. For dimensioning resistor sizes please take bus capacity and communication frequency into account (see for example 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. It is recommended to wire the sensor according to the application circuit as shown in Figure 2. Figure 2: Typical application circuit. Please note that the positioning of the pins does not reflect the position on the real sensor. This is shown in Table 1. The pin numbers corresponding to the schematic in Table 1 are indicated. 4.3.3 Address Selection Pin (ADDR) A resistor between ADDR and VDD may be used to configure the I2C address the STC31 uses for communication. Table 2 shows the selectable addresses and their respective conditions. I2C Address in Hex. Condition representation 0x29 (default) Ground or no connection between ADDR (pin 3) and VDD (pin 6) 0x2A 10 kOhm between ADDR (pin 3) and VDD (pin 6) 0x2B 3.3 kOhm between ADDR (pin 3) and VDD (pin 6) 0x2C 1 kOhm between ADDR (pin 3) and VDD (pin 6) Table 2: STC31 I2C addresses 4.3.4 Die Pad (Center Pad) The die pad or center pad is visible from below and located in the center of the package. It is internally connected to GND and therefore, there are no electrical constraints on connecting or not connecting the die pad to GND. 10 http://www.nxp.com/documents/user_manual/UM10204.pdf www.sensirion.com – Confidential D1 Version 1.1 – October 2020 13/16 5. Sensor Integration 5.1 Compensation of Humidity and Temperature Both the temperature and the absolute humidity influence the thermal conductivity. The temperature is compensated by the STC31 sensor automatically. The STC31 has the option to compensate for the humidity. The relative humidity has to be communicated to the STC31, and with this information the sensor will output a compensated concentration value. When no humidity value is given to the STC31, the sensor assumes a relative humidity of 0%. To measure the relative humidity Sensirion’s SHTC3 humidity sensor is recommended. When using the SHTC3, it is also recommended to feed the temperature of the SHTC3 to the STC31, because the SHTC3 has a higher temperature accuracy. Sections 3.3.3 and 3.3.4 describe how the humidity and temperature values can be written to the STC31. In most of the cases pressure changes related to weather can be neglected. However, it is recommended to compensate pressure deviations from 1013mbar as shown in section 3.3.5. Important note: It is very important that the humidity sensor measures the humidity and temperature of the gas surrounding the STC31 sensor. The humidity sensor must be placed as close as possible to the STC31 sensor. Airflows might result in temperature differences, which will result in inaccurate values used for compensation. Additionally, thermal coupling precautions as mentioned in section 5.2 become even more relevant when using both sensors. 5.2 Thermal Coupling The STC31 uses a thermal principle to measure gas concentrations. This implies that the sensor is sensitive to external heat sources or self-heating. Consider the following:  Reduce I2C communication with the sensor to a minimum  Increase the time between measurements as much as possible. At least one second must be between measurements.  Prefer a high resistance pull-up resistor to a low resistance pull-up resistor.  Thermally decouple the I2C bus from the MCU if the MCU can get hot and the I2C bus is short.  Prevent sources emitting infrared to the sensor element.  Keep the sensor away from other components that somehow can transfer heat to the sensor, e.g. power converters, motors, etc. 5.3 Gas Flows Gas flows might affect the thermal balance between the STC31, SHTC3 and the PCB, which could influence the accuracy of the gas concentration measurements. If the gas concentration needs to be measured in a flow, it is advised to create some kind of dead space that is well vented, but keeps the sensor(s) out of the direct flow of the gas. www.sensirion.com – Confidential D1 Version 1.1 – October 2020 14/16 6. Shipping Package STC31 is provided in tape & reel shipment packaging. Standard packaging size is 400 or 5000 units per reel. Figure 3 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. 7. Ordering Information Use the part names and product numbers shown in the following table when ordering STC31 Thermal Conductivity Sensor. For the latest product information and local distributors, visit www.sensirion.com. Part name Description / Output STC31-R3 STC31-R5 I2C Order number Packaging Tape & Reel size 3.000.331 Tape & Reel 400 3.000.160 Tape & Reel 5000 Revision History Date Author Version Changes 23.10.2020 JGOE V1.1 Clarifications www.sensirion.com – Confidential D1 Version 1.1 – October 2020 15/16 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 (including death). 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 datasheet 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. See application note “Handling Instructions” for more information. Warranty SENSIRION warrants solely to the original purchaser of this product for a period of 12 months (one year) from the date of delivery that this 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 datasheet 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 © 2019, 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.co.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.co.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 www.sensirion.com – Confidential D1 Version 1.1 – October 2020 16/16