BME680

Bosch Sensortec | BME680 Datasheet 1 | 50 BME680 Low power gas, pressure, temperature & humidity sensor BME680 – Datasheet Document revision 1.0 Document release date July 2017 Document number BST-BME680-DS001-00 Technical reference code(s) 1 277 340 511 Notes Data and descriptions in this document are subject to change without notice. Product photos and pictures are for illustration purposes only and may differ from the real product appearance. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 2 | 50 BME680 Low power gas, pressure, temperature & humidity sensor The BME680 is a digital 4-in-1 sensor with gas, humidity, pressure and temperature measurement based on proven sensing principles. The sensor module is housed in an extremely compact metal-lid LGA package with a footprint of only 3.0 × 3.0 mm² with a maximum height of 1.00 mm (0.93 ± 0.07 mm). Its small dimensions and its low power consumption enable the integration in battery-powered or frequency-coupled devices, such as handsets or wearables. Typical applications  Indoor air quality  Home automation and control  Internet of things  Weather forecast  GPS enhancement (e.g. time-to-first-fix improvement, dead reckoning, slope detection)  Indoor navigation (change of floor detection, elevator detection)  Outdoor navigation, leisure and sports applications  Vertical velocity indication (rise/sink speed) Target Devices  Handsets such as mobile phones, tablet PCs, GPS devices  Wearables  Home weather stations  Smart watches  Navigation systems  Gaming, e.g. flying toys  IOT devices Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 3 | 50 Key features  Package  Digital interface  Supply voltage     3.0 mm x 3.0 mm x 0.93 mm metal lid LGA I²C (up to 3.4 MHz) and SPI (3 and 4 wire, up to 10 MHz) VDD main supply voltage range: 1.71 V to 3.6 V VDDIO interface voltage range: 1.2 V to 3.6 V Current consumption 2.1 µA at 1 Hz humidity and temperature 3.1 µA at 1 Hz pressure and temperature 3.7 µA at 1 Hz humidity, pressure and temperature 0.09‒12 mA for p/h/T/gas depending on operation mode 0.15 µA in sleep mode Operating range -40‒+85 °C, 0‒100% r.H., 300‒1100 hPa Individual humidity, pressure and gas sensors can be independently enabled/disabled The product is RoHS compliant, halogen-free, MSL1 Key parameters for gas sensor  Response time (𝜏33−63% )  Power consumption  Output data processing < 1 s (for new sensors) < 0.1 mA in ultra-low power mode direct indoor air quality (IAQ) index output Key parameters for humidity sensor  Response time (𝜏0−63% )  Accuracy tolerance  Hysteresis ~8 s ±3% r.H. ±1.5% r.H. Key parameters for pressure sensor  RMS Noise  Offset temperature coefficient 0.12 Pa, equiv. to 1.7 cm ±1.3 Pa/K, equiv. to ±10.9 cm at 1 °C temperature change Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 4 | 50 Table of contents 1. Specification 7 1.1 General Electrical Specification ............................................................................................................................ 7 1.2 Gas sensor specification ....................................................................................................................................... 8 1.3 Humidity sensor specification .............................................................................................................................. 10 1.4 Pressure sensor specification ............................................................................................................................. 11 1.5 Temperature sensor specification ....................................................................................................................... 12 2. Absolute maximum ratings 13 3. Sensor usage 14 3.1 Sensor modes ..................................................................................................................................................... 14 3.2 Sensor configuration ........................................................................................................................................... 15 3.2.1 Quick start ........................................................................................................................................................ 15 3.2.2 Sensor configuration flow ................................................................................................................................. 16 3.3 Measurement flow ............................................................................................................................................... 17 3.3.1 Temperature measurement .............................................................................................................................. 17 3.3.2 Pressure measurement .................................................................................................................................... 17 3.3.3 Humidity measurement .................................................................................................................................... 17 3.3.4 IIR filter ............................................................................................................................................................. 18 3.3.5 Gas sensor heating and measurement ............................................................................................................ 18 3.4 Data readout........................................................................................................................................................ 19 3.4.1 Gas resistance readout .................................................................................................................................... 19 3.5 Output compensation .......................................................................................................................................... 19 4. Software and use cases 21 4.1 BSEC software .................................................................................................................................................... 21 4.2 Indoor-air-quality ................................................................................................................................................. 23 5. Global memory map and register description Modifications reserved |Data subject not change without notice | Printed in Germany 24 Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 5 | 50 5.1 General remarks ................................................................................................................................................. 24 5.2 Memory map ....................................................................................................................................................... 25 5.3 Register description ............................................................................................................................................ 26 5.3.1 General control registers .................................................................................................................................. 26 5.3.2 TEMPERATURE, PRESSURE AND RELATIVE HUMIDITY CONTROL REGISTERS 5.3.4 DATA REGISTERS 5.3.5 STATUS REGISTERS 6. Digital interfaces 27 32 33 35 6.1 Interface selection ............................................................................................................................................... 35 6.2 I²C Interface......................................................................................................................................................... 35 6.2.1 I²C WRITE 6.2.2 I²C READ 36 36 6.3 SPI interface ........................................................................................................................................................ 37 6.3.1 SPI WRITE 6.3.2 SPI READ 37 38 6.4 Interface parameter specification ........................................................................................................................ 38 6.4.1 General interface parameters .......................................................................................................................... 38 6.4.2 I²C timings ........................................................................................................................................................ 39 6.4.3 SPI TIMINGS 7. Pin-out and connection diagram 40 41 7.1 Pin-out ................................................................................................................................................................. 41 7.2 Connection diagrams .......................................................................................................................................... 42 7.3 Package dimensions ........................................................................................................................................... 43 7.4 Landing pattern recommendation ....................................................................................................................... 44 7.5 Marking ................................................................................................................................................................ 45 7.5.1 Mass production devices.................................................................................................................................. 45 7.5.2 Engineering samples ........................................................................................................................................ 45 7.6 Soldering guidelines and reconditioning recommendations ............................................................................... 46 7.7 Mounting and assembly recommendations ........................................................................................................ 46 7.8 Environmental safety ........................................................................................................................................... 47 7.8.1 RoHS ................................................................................................................................................................ 47 7.8.2 Halogen content ............................................................................................................................................... 47 Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 6 | 50 7.8.3 Internal package structure ................................................................................................................................ 47 8. Legal disclaimer ............................................................................................................................................48 8.1 Engineering samples ........................................................................................................................................... 48 8.2 Product use ......................................................................................................................................................... 48 8.3 Application examples and hints ........................................................................................................................... 48 9. Document history and modifications ..................................................................................................49 Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 7 | 50 1. Specification If not stated otherwise,       all values are valid over the full voltage range, all minimum/maximum values are given for the full accuracy temperature range minimum/maximum values of drifts, offsets and temperature coefficients are ±3 values over lifetime, typical values of currents and state machine timings are determined at 25 °C, minimum/maximum values of currents are determined using corner lots over complete temperature range, and minimum/maximum values of state-machine timings are determined using corner lots over 0‒+65 °C temperature range. Besides the general electrical specifications, the following tables are separated for the gas, pressure, humidity and temperature functions of the BME680. 1.1 General Electrical Specification Table 1: Electrical parameter specification OPERATING CONDITIONS BME680 1 Parameter Symbol Condition Min Typ Max Unit Supply Voltage Internal Domains1 VDD ripple max. 50 mVpp 1.71 1.8 3.6 V Supply Voltage I/O Domain VDDIO 1.2 1.6 3.6 V Sleep current IDDSL 0.15 1 µA Standby current (inactive period of normal mode) IDDSB 0.29 0.8 µA Current during humidity measurement IDDH Max value at 85 °C 340 450 µA Current during pressure measurement IDDP Max value at -40 °C 714 849 µA Current during temperature measurement IDDT Max value at 85 °C 350 Start-up time tstartup Time to first communication after both VDD > 1.58 V and VDDIO > 0.65 V 2 ms Power supply rejection ratio (DC) PSRR full VDD range ±0.01 ±5 %r.H./V Pa/V Standby time accuracy Δtstandby ±25 % ±5 µA The power efficiency, performance and heat dissipation scales with the applied supply voltage. The BME680 is optimized for 1.8 V. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 8 | 50 1.2 Gas sensor specification Table 2 lists the gas sensor specification. All the parameters are deduced from lab measurements under controlled environmental conditions, which are compliant to the ISO16000-29 standard “Test methods for VOC detectors”. Detailed procedure to measure the gas sensor is available in the Application Note: Measurement Instructions for Lab Environment. Referring to Chapter 4, a software solution (BSEC: Bosch Software Environmental Cluster) is available for the BME680. The software is carefully engineered to seamlessly work with the 4-in-1 integrated sensors inside the BME680. Based on an intelligent algorithm, the BSEC provides an indoor air quality (IAQ) output. In principle, this output is in an index that can have values between 0 and 500 with a resolution of 1 to indicate or quantify the quality of the air available in the surrounding. Table 4 lists the IAQ system specification. The detailed classification and color coding of the IAQ index is described in Table 4. Furthermore, the BSEC solution supports different operation modes for the gas sensor to address the necessary power budget and update rate requirements of the end-application. Unless mentioned otherwise, the specifications are deduced from new sensors that have been operated for at least five days mainly in ambient air and consequently have the same history (i.e. same power mode and exposed to the same environment). Besides ethanol (EtOH) as a target test gas, the sensors are also tested with breath-VOC (b-VOC). The b-VOC mixture, as listed in Table 5, represents the most important compounds in an exhaled breath of healthy humans. The values are derived from several publications on breath analysis studies. The composition does not contain species which would chemically react to ensure that the mixture is stable for at least 6 months. Furthermore, the composition is also limited to species which can be manufactured in one mixture. Table 2: Gas sensor parameter specification Parameter Symbol Condition Operational range1 Supply Current during heater operation Peak Supply Current Average Supply Current (VDD ≤ 1.8 V, 25°C) Response time2 (brand-new sensors) Typ Max Unit -40 85 °C 10 95 % r.H. IDD Heater target temperature 320 °C, constant operation (VDD ≤ 1.8 V, 25°C) 9 12 13 mA IPeak Occurs within first ms of switching on the hotplate 15 17 18 mA Ultra-low power mode 0.09 mA Low power mode 0.9 mA Continuous mode 12 mA τ33-63% Ultra-low power mode 92 s τ33-63% Low power mode 1.4 s τ33-63% Continuous mode 0.75 s IDD,IAQ Resolution of gas sensor resistance measurement Noise in gas sensor resistance (RMS) Min 0.05 NR 0.08 1.5 0.11 % % 1 The sensors are electrically operable within this range. Actual performance may vary Response time of unsoldered, brand-new sensors extracted from the sensors’ resistance change in response to a 0.6–60 ppm step of EtOH and a 0.5–15 ppm step of b-VOC at 20 °C, 50% r.H. and atmospheric pressure. 2 Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 9 | 50 Table 3: IAQ system parameter specification3 Parameter Symbol Condition Min Typ Accuracy status4 AXIAQ Android compatible 0 IAQ Resolution IAQrs IAQ Range IAQrg Sensor-to-sensor deviation5 IAQS2S All operation modes ±15% ±15 IAQS2S Sensor-to-sensor deviation ±15% ±15 IAQdrift Drift at low & high concentrations ±1% ±4 Max Unit 3 1 0 Durability to siloxanes6,7,8 500 Table 4: Indoor air quality (IAQ) classification and color-coding9 IAQ Index Air Quality 0 – 50 good10 51 – 100 average 101 – 150 little bad 151 – 200 bad 201 – 300 worse2 301 – 500 very bad Table 5: bVOC mixture with Nitrogen as carrier gas Molar fraction Compound Production tolerance Certified accuracy 5 ppm Ethane 20 % 5% 10 ppm Isoprene /2-methyl-1,3 Butadiene 20 % 5% 10 ppm Ethanol 20 % 5% 50 ppm Acetone 20 % 5% 15 ppm Carbon Monoxide 10 % 2% 3 IAQ parameters only apply for the combination of BME680 together with the Bosch Software Environmental Cluster (BSEC) solution (available separately, see Chapter 4) The accuracy status is equal to zero during the power-on stabilization times of the sensor and is equal to 3 when the sensor achieves best performance 5 Tested with 0.6–90 ppm of EtOH at 5–40 °C, 20–80% r.H. and atmospheric pressure. Condition is valid after the calibration period of the BSEC algorithm. 6 Siloxanes are present in a typical indoor environment and can in principle perturb the metal-oxide-based gas sensor performance. 7 220 hours of 700 mg/m3 of octamethylcyclotetrasiloxane (D4) in ambient conditions (i.e. 20 °C and 50% r.H.) simulates the amount of siloxanes in a typical indoor environment over more than 10 years. 8 Tested with 0.5–15 ppm of b-VOC at 20 °C and 50% r.H. using continuous operation mode for 220 hours of 700 mg/m 3 of octamethylcyclotetrasiloxane (D4). 9 According to the guidelines issued by the German Federal Environmental Agency, exceeding 25 mg/m3 of total VOC leads to headaches and further neurotoxic impact on health. 10 The BSEC software auto-calibrates the low and high concentrations applied during testing to IAQ of 25 and 250, respectively. 4 Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 10 | 50 1.3 Humidity sensor specification Table 6: Humidity parameter specification Parameter Symbol Condition Operating Range11 Full accuracy range 1 Hz forced mode, temperature and humidity measurement Min Typ Max Unit -40 25 85 °C 0 100 % r.H. 0 65 °C 10 90 % r.H. 2.8 µA 2.1 Supply Current IDD,H Absolute Accuracy AH 20‒80 % r.H., 25 °C, including hysteresis ±3 % r.H. Hysteresis12 HH 10→90→10 % r.H., 25°C ±1.5 % r.H. Nonlinearity13 NLH 10→90 % r.H., 25°C 1.7 % r.H. Response time to complete 63% of step14 τ0-63% N2 (dry) → 90 % r.H., 25°C 8 s Resolution RH 0.008 % r.H. Noise in humidity (RMS) NH Highest oversampling 0.01 % r.H. Long-term stability ∆Hstab 10‒90 % r.H., 25°C 0.5 % r.H./ year 11 When exceeding the operating range (e.g. for soldering), humidity sensing performance is temporarily degraded and reconditioning is recommended as described in Section 7.7. Operating range only for non-condensing environment. 12 For hysteresis measurement the sequence 0103050709070503010 % r.H. is used. The hysteresis is defined as the maximum difference between measurements at of the same humidity up / down branch and the averaged curve of both branches. 13 Non-linear contributions to the sensor data are corrected during the calculation of the relative humidity by the compensation formulas described in Section 3.5. 14 The air-flow in direction to the vent-hole of the device has to be dimensioned in a way that a sufficient air exchange inside to outside will be possible. To observe effects on the response time-scale of the device an air-flow velocity of approximately 1 m/s is needed. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 11 | 50 1.4 Pressure sensor specification Table 7: Pressure parameter specification Parameter Symbol Condition Min Typ Max Operating temperature range TA Operating pressure range operational -40 25 85 full accuracy 0 65 P full accuracy 300 1100 hPa Supply current IDD,LP 1 Hz forced mode, pressure and temperature, lowest power 4.2 µA Temperature coefficient of offset15 TCOP 25‒40 °C, 900 hPa Ap, full 300‒1100 hPa 0‒65°C Absolute accuracy pressure 3.1 Unit °C ±1.3 Pa/K ±10.9 cm/K ±0.6 hPa ±0.12 hPa 700‒900hPa, Arel Relative accuracy pressure Resolution of pressure output data Noise in pressure 900‒1100hPa Arel 25‒40 °C, at constant humidity ±0.12 hPa RP Highest oversampling 0.18 Pa Full bandwidth, highest oversampling 1.4 Pa 11 cm Reduced bandwidth, highest oversampling 0.2 Pa 1.7 cm NP,fullBW Solder drift 15 16 25‒40 °C, at constant humidity Minimum solder height 50µm Long-term stability16 Pstab per year Possible sampling rate fsample_P Lowest oversampling, see chapter 3.3.2 -0.5 157 1.2 +2.0 hPa ±1.0 hPa 182 Hz When changing temperature from 25 °C to 40 °C at constant pressure / altitude, the measured pressure / altitude will change by (15×TCOP). Long-term stability is specified in the full accuracy operating pressure range 0‒65 °C Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 12 | 50 1.5 Temperature sensor specification Table 8: Temperature parameter specification Parameter Symbol Condition Min Typ Max Unit Operating temperature range TA operational -40 25 85 °C IDD,T 1 Hz forced mode, temperature measurement only 1.0 µA AT,25 25 °C ±0.5 °C AT,full 0‒65 °C ±1.0 °C Output resolution RT API output resolution 0.01 °C RMS noise NT Lowest oversampling 0.005 °C Supply current Absolute accuracy temperature17 17 Temperature measured by the internal temperature sensor. This temperature value depends on the PCB temperature, sensor element self-heating and ambient temperature and is typically above ambient temperature. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 13 | 50 2. Absolute maximum ratings The absolute maximum ratings are determined over the complete temperature range using corner lots. The values are provided in Table 9. Table 9: Absolute maximum ratings Parameter Condition Min Max Unit Voltage at any supply pin VDD and VDDIO pin -0.3 4.25 V -0.3 VDDIO + 0.3 V -45 +85 °C 0 20 000 hPa HBM, at any pin ±2 kV Machine model ±200 V Voltage at any interface pin Storage temperature ≤ 65% r.H. Pressure ESD Condensation No power supplied Modifications reserved |Data subject not change without notice | Printed in Germany Allowed Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 14 | 50 3. Sensor usage 3.1 Sensor modes The sensor supports low-level power modes: sleep and forced mode. These modes can be selected using the mode control register (see Section 5.3.1.3). The key differences between the modes are summarized in Table 10. After a power-up sequence, the sensor automatically starts in sleep mode. If the device is currently performing a measurement, execution of mode switching commands is delayed until the end of the currently running measurement period. It is important to note that, further mode change commands or other write commands to the control registers are ignored until the mode change command has been executed. All control registers should be set to the desired values before writing to the mode register. Table 10: Low-level operation modes Operation mode mode Key features Sleep 00   No measurements are performed Minimal power consumption Forced mode 01    Single TPHG cycle is performed Sensor automatically returns to sleep mode afterwards Gas sensor heater only operates during gas measurement In forced mode, temperature, pressure, humidity and gas conversion are performed sequentially. Such a measurement cycle is abbreviated as TPHG (Temperature, Pressure, Humidity and Gas) in the following descriptions. Up to 10 temperature setpoints and heating durations for the gas sensor hot plate can be stored in the sensor registers. In the following, these setpoints and the corresponding measurements are identified as G 0 – G9.Figure 1 illustrates the handling of these measurement sequences and the gas sensor hot plate is heated for the forced mode. Figure 1: Sequence of ADC and gas sensor heater operation Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 15 | 50 3.2 Sensor configuration 3.2.1 Quick start The sensor is configured by writing to a set of control registers (see Chapter 5 for a detailed list of all available registers and their descriptions). This section illustrates, with the help of a basic step-by-step example, how to configure the sensor for simple forced mode measurements with a single heater set-point. For a more detailed description of the measurement flow, please refer to Section 3.3. In this example, the sensor will be configured to use 2x oversampling for its temperature measurements, 16x oversampling for the pressure signal, and 1x oversampling for humidity. Moreover, the gas sensor hot plate will be configured to be heated for 100 ms at 300 °C before the gas measurement is performed. First, the user must configure the oversampling settings for temperature, pressure and humidity by setting the control registers osrs_t and osrs_h, respectively. Supported settings range from 16x oversampling down to 0x, which is equivalent to skipping the corresponding sub-measurement. See Section 5.3.2 for further details. 1. Set humidity oversampling to 1x by writing 0b001 to osrs_h 2. Set temperature oversampling to 2x by writing 0b010 to osrs_t 3. Set pressure oversampling to 16x by writing 0b101 to osrs_p It is highly recommended to set first osrs_h followed by osrs_t and osrs_p in one write command (see Section 3.3). Next, the user shall set at least one gas sensor hot plate temperature set-point and heating duration. Up to 10 heating duration can be configured through the control registers gas_wait_x, where x ranges from 0 to 9. See Section 5.3.3 for definition of register content. The corresponding heater set-points are stored in the registers res_heat_x. Section 3.3.5 explains how to convert the target heater temperature, e.g. 300 °C, into a register code. For forced mode operation, the used heater set point is selected by setting the control register nb_conv to the heater profile to be used, e.g. to use gas_wait_0 and res_heat_0, nb_conv shall be set to 0x0. Finally, gas functionality shall be enabled by setting the run_gas_l bit to 1. 4. 5. 6. 7. Set gas_wait_0 to 0x59 to select 100 ms heat up duration Set the corresponding heater set-point by writing the target heater resistance to res_heat_0 Set nb_conv to 0x0 to select the previously defined heater settings Set run_gas_l to 1 to enable gas measurements Now, a single forced mode measurement with the above settings can be triggered by writing 0b01 to mode. For more details on data readout, please see Section 5.3.1.3. 8. Set mode to 0b01 to trigger a single measurement. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 16 | 50 3.2.2 Sensor configuration flow Picture 2 illustrates which control registers must be set. For details on the individual control registers, please refer to Chapter 5. Moreover, details on the measurement flow for the individual modes can be found in Section 3.3. Forced Mode Select oversampling for T, P and H • Set osrs_x Select IIR filter for temperature sensor • Set filter Enable gas coversion • Set run_gas to 1 Select index of heater set-point • Set nb_conv (indexing is zero-based) Define heater-on time • Convert duration to register code • Set gas_wait_x (time base unit is ms) Set heater temperature • Convert temperature to register code • Set res_heat_x Set mode to forced mode • Set mode to 0b01 Picture 2: Sensor configuration flow Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 17 | 50 3.3 Measurement flow Referring to Figure 1, the BME680 measurement period consists of a temperature, pressure and humidity measurement with selectable oversampling. Moreover, it contains a heating phase for the gas sensor hot plate as well as a measurement of the gas sensor resistance. After the measurement period, the pressure and temperature data can be passed through an optional IIR filter, which removes short-term fluctuations. For humidity and gas, such a filter is not needed and has not been implemented. 3.3.1 Temperature measurement Temperature measurement can be enabled or skipped. Skipping the measurement is typically not recommended since temperature information is used to compensate temperature influences in the other parameters. When enabled, several oversampling options exist. The temperature measurement is controlled by the osrs_t setting which is detailed in Section 5.3.2.2. For the temperature measurement, oversampling is possible to reduce the noise. The resolution of the temperature data depends on the IIR filter (see Section 5.3.2.4) and the oversampling setting:  When the IIR filter is enabled, the temperature resolution is 20 bit  When the IIR filter is disabled, the temperature resolution is 16 + (osrs_t – 1) bit, e.g. 18 bit when osrs_t is set to ‘3’ 3.3.2 Pressure measurement Pressure measurement can be enabled or skipped. When enabled, several oversampling options exist. The pressure measurement is controlled by the osrs_p setting which is detailed in Section 5.3.2. For the pressure measurement, oversampling is possible to reduce noise. The resolution of the pressure data depends on the IIR filter (see Section 5.3.2.4) and the oversampling setting:  When the IIR filter is enabled, the pressure resolution is 20 bit  When the IIR filter is disabled, the pressure resolution is 16 + (osrs_p – 1) bit, e.g. 18 bit when osrs_p is set to ‘3’ 3.3.3 Humidity measurement The humidity measurement can be enabled or skipped. When enabled, several oversampling options exist. The humidity measurement is controlled by the osrs_h setting, which is described in detail in Section 5.3.2.1. For the humidity measurement, oversampling is possible to reduce noise. The resolution of the humidity measurement is fixed at 16 bit ADC output. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 18 | 50 3.3.4 IIR filter The environmental pressure is subject to many short-term changes, caused external disturbances. To suppress disturbances (e.g. slamming of door or wind blowing into the sensor) in the output data without causing additional interface traffic and processor work load, the BME680 features an internal IIR filter (see Section 5.3.2.4). It effectively reduces the bandwidth of the temperature and pressure output signals and increases the resolution of the output data to 20 bit, noting that the humidity and gas values inside the sensor does not fluctuate rapidly and does not require low pass filtering. The output of a next measurement step is filtered using the following formula: 𝑥𝑓𝑖𝑙𝑡 [𝑛] = 𝑥𝑓𝑖𝑙𝑡 [𝑛 − 1] ∙ (𝑐 − 1) + 𝑥𝐴𝐷𝐶 𝑐 𝑥𝑓𝑖𝑙𝑡 [𝑛 − 1] is the data coming from the current filter memory, and 𝑥𝐴𝐷𝐶 is the data coming from current ADC acquisition. 𝑥𝑓𝑖𝑙𝑡 [𝑛] denotes the new value of filter memory and the value that will be sent to the output registers. The IIR filter can be configured to different filter coefficients, which slows down the response to the sensor inputs. Note that the response time with enabled IIR filter depends on the number of samples generated, which means that the data output rate must be known to calculate the actual response time. When writing to the register filter, the filter is reset. The next ADC values will pass through the filter unchanged and become the initial memory values for the filter. If temperature or pressure measurements are skipped, the corresponding filter memory will be kept unchanged even though the output registers are set to 0x80000. When the previously skipped measurement is re-enabled, the output will be filtered using the filter memory from the last time when the measurement was not skipped. If this is not desired, please write to the filter register in order to re-initialize the filter. 3.3.5 Gas sensor heating and measurement The operation of the gas sensing part of BME680 involves two steps: 1. Heating the gas sensor hot plate to a target temperature (typically between 200 °C and 400 °C) and keep that temperature for a certain duration of time. 2. Measuring the resistance of the gas sensitive layer. Up to 10 different hot plate temperature set points can be configured by setting the registers res_heat_x, where x = 0…9 .The internal heater control loop operates on the resistance of the heater structure. Hence, the user first needs to convert the target temperature into a device specific target resistance before writing the resulting register code into the sensor memory map. The following code will calculate register code that to be written to res_heat_x. Nevertheless, it is recommended to use the sensor API available on github (Chapter 4) for a friendlier user experience. var1 = ((double)par_g1 / 16.0) + 49.0; var2 = (((double)par_g2 / 32768.0) * 0.0005) + 0.00235; var3 = (double)par_g3 / 1024.0; var4 = var1 * (1.0 + (var2 * (double) target_temp)); var5 = var4 + (var3 * (double)amb_temp); res_heat_x = (uint8_t)(3.4 * ((var5 * (4.0 / (4.0 + (double)res_heat_range)) * (1.0/(1.0 + ((double)res_heat_val * 0.002)))) - 25)); where        par_g1, par_g2, and par_g3 are calibration parameters, target_temp is the target heater temperature in degree Celsius, amb_temp is the ambient temperature (hardcoded or read from temperature sensor), var5 is the target heater resistance in Ohm, res_heat_x is the decimal value that needs to be stored in register, where ‘x’ corresponds to the temperature profile number between 0 and 9, res_heat_range is the heater range stored in register address 0x02 , and res_heat_val is the heater resistance correction factor stored in register address 0x00 (signed, value from -128 to 127). Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 19 | 50 Table 11: Variable names and register addresses for res_heat_x calculation Variable name Register address (LSB / MSB) par_g1 0xED par_g2 0xEB/0xEC par_g3 0xEE res_heat_range 0x02 res_heat_val 0x00 For each of the 10 temperature set-points, the heating duration must be specified. Referring to Figure 1, the heating phase starts after the temperature, pressure and humidity measurements are complete. This means there is no heating in parallel to these measurements, which is desirable to minimize undesired cross-influences between the various sensor components. The heating duration is specified by writing to the corresponding gas_wait_x control register. Heating durations between 1 ms and 4032 ms can be configured. In practice, approximately 20–30 ms are necessary for the heater to reach the intended target temperature. 3.4 Data readout The procedure goes as follows, the new_data_x bit (see Section 5.3.5.1) can be checked to see if a new data is generated. If gas measurements are performed the gas_valid_r (see Section 5.3.5.5) and heat_stab_r (see Section 5.3.5.6) status bits of the respectively field should be checked to ensure that the gas measurement was successful. If heat_stab_r is zero, it indicates that either the heating time was not sufficient to allow the sensor to reach to configured target temperature or that the target temperature was too high for the sensor to reach. After the uncompensated values of temperature, pressure and humidity have been read, the actual humidity, pressure and temperature need to be calculated using the compensation parameters stored in the device. Please refer to the BME6xy API for more details. 3.4.1 Gas resistance readout Readout of gas resistance ADC value and calculation of gas resistance consists of 3 steps 1. Read gas ADC value (gas_r) and gas ADC range (gas_range_r) (see Section 5.3.4) 2. Read range switching error from register address 0x04 (signed 4 bit) 3. Convert ADC value into gas resistance in ohm The conversion is done as follows: var1 = (1340.0 + 5.0 * range_switching_error) * const_array1[gas_range]; gas_res = var1 * const_array2[gas_range] / (gas_r - 512.0 + var1); 3.5 Output compensation The BME680 output consists of the ADC output values. However, each sensing element behaves differently. Therefore, the actual humidity, pressure and temperature must be calculated using a set of calibration parameters. This is implemented in the BME6xy API. Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 20 | 50 Table 12: List of gas ranges and corresponding constants used for the resistance calculation gas_range Constants (to be integrated in the driver) const_array1 const_array2 0 1 8000000 1 1 4000000 2 1 2000000 3 1 1000000 4 1 499500.4995 5 0.99 248262.1648 6 1 125000 7 0.992 63004.03226 8 1 31281.28128 9 1 15625 10 0.998 7812.5 11 0.995 3906.25 12 1 1953.125 13 0.99 976.5625 14 1 488.28125 15 1 244.140625 Modifications reserved |Data subject not change without notice | Printed in Germany Document number: BST-BME680-DS001-00 Revision_1.0_072017 Bosch Sensortec | BME680 Datasheet 21 | 50 4. Software and use cases 4.1 BSEC software BME680 sensor is intended to be used together with Bosch Software Environmental Cluster (BSEC) solution and BME6xy sensor API to unlock its full potential. The BSEC software features intelligent algorithms which enable use cases such as indoor-air-quality monitoring using the BME680. Bosch Sensortec BSEC software is available as a closed source binary which will be made available via a Software License Agreement (SLA) on the Bosch Sensortec website (https://www.bosch-sensortec.com/bst/products/all_products/BSEC). Sensor API covers basic sensor communication and data compensation functions and is available as open-source code from Github (https://github.com/BoschSensortec/BME680_driver). The key features of the hardware-software system are:    Calculation of ambient air temperature outside of the device (e.g. phone) Calculation of ambient relative humidity outside of the device Calculation of indoor air quality (IAQ) level outside of the device Moreover, the software algorithms handle humidity compensation, baseline as well as long-term drift correction of the gas sensor signal. Different power modes for the gas sensor and corresponding data rates are supported by the software solution:    Ultra low power (ULP) mode that is designed for battery-powered and/or frequency-coupled devices over extended periods of time. This mode features an update rate of 300 seconds and an average current consumption of