SI7021-A20-GM_温湿度传感器

hytech

Rev. 1.2 8/16 Copyright © 2016 by Silicon Laboratories Si7021-A20Si7021-A20I2C HUMIDITY AND TEMPERATURE SENSORFeaturesApplicationsDescriptionThe Si7021 I2C Humidity and Temperature Sensor is a monolithic CMOS ICintegrating humidity and temperature sensor elements, an analog-to-digitalconverter, signal processing, calibration data, and an I2C Interface. The patenteduse of industry-standard, low-K polymeric dielectrics for sensing humidity enablesthe construction of low-power, monolithic CMOS Sensor ICs with low drift andhysteresis, and excellent long term stability.The humidity and temperature sensors are factory-calibrated and the calibrationdata is stored in the on-chip non-volatile memory. This ensures that the sensorsare fully interchangeable, with no recalibration or software changes required.The Si7021 is available in a 3x3 mm DFN package and is reflow solderable. It canbe used as a hardware- and software-compatible drop-in upgrade for existing RH/temperature sensors in 3x3 mm DFN-6 packages, featuring precision sensingover a wider range and lower power consumption. The optional factory-installedcover offers a low profile, convenient means of protecting the sensor duringassembly (e.g., reflow soldering) and throughout the life of the product, excludingliquids (hydrophobic/oleophobic) and particulates.The Si7021 offers an accurate, low-power, factory-calibrated digital solution idealfor measuring humidity, dew-point, and temperature, in applications ranging fromHVAC/R and asset tracking to industrial and consumer platforms. Precision Relative Humidity Sensor ± 3% RH (max), 0–80% RH High Accuracy Temperature Sensor±0.4 °C (max), –10 to 85 °C 0 to 100% RH operating range Up to –40 to +125 °C operatingrange Wide operating voltage(1.9 to 3.6 V) Low Power Consumption150 µA active current60 nA standby current Factory-calibrated I2C Interface Integrated on-chip heater 3x3 mm DFN Package Excellent long term stability Optional factory-installed coverLow-profileProtection during reflowExcludes liquids and particulates HVAC/R Thermostats/humidistats Respiratory therapy White goods Indoor weather stations Micro-environments/data centers Automotive climate control anddefogging Asset and goods tracking Mobile phones and tabletsPatent Protected. Patents pendingOrdering Information:See page 29.Pin AssignmentsDNCSCLVDD126GND 5SDA3 4 DNCTop ViewSi7021-A202 Rev. 1.2Functional Block DiagramADCGNDHumiditySensorControl LogicSCLSi7021TempSensor1.25VRefI2C InterfaceSDAVddCalibrationMemorySi7021-A20Rev. 1.2 3TABLE OF CONTENTSSection Page1. Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42. Typical Application Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113. Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124. Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134.1. Relative Humidity Sensor Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144.2. Hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154.3. Prolonged Exposure to High Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154.4. PCB Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154.5. Protecting the Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174.6. Bake/Hydrate Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174.7. Long Term Drift/Aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175. I2C Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185.1. Issuing a Measurement Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195.2. Reading and Writing User Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .235.3. Electronic Serial Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .235.4. Firmware Revision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245.5. Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .256. Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266.1. Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .267. Pin Descriptions: Si7021 (Top View) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288. Ordering Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299. Package Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .309.1. Package Outline: 3x3 6-pin DFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .309.2. Package Outline: 3x3 6-pin DFN with Protective Cover . . . . . . . . . . . . . . . . . . . . . .3110. PCB Land Pattern and Solder Mask Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3211. Top Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3311.1. Si7021 Top Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3311.2. Top Marking Explanation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3312. Additional Reference Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Document Change List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35Si7021-A204 Rev. 1.21. Electrical SpecificationsUnless otherwise specified, all min/max specifications apply over the recommended operating conditions.Table 1. Recommended Operating ConditionsParameter Symbol Test Condition Min Typ Max UnitPower Supply VDD 1.9 — 3.6 VOperating Temperature TA I and Y grade –40 — +125 °COperating Temperature TA G grade –40 — +85 °CTable 2. General Specifications1.9 < VDD < 3.6 V; TA = –40 to 85 °C (G grade) or –40 to 125 °C (I/Y grade); default conversion time unless otherwise noted.Parameter Symbol Test Condition Min Typ Max UnitInput Voltage High VIH SCL, SDA pins 0.7xVDD — —VInput Voltage Low VIL SCL, SDA pins — — 0.3xVDD VInput Voltage Range VIN SCL, SDA pins with respect to GND 0.0 — VDD VInput Leakage IIL SCL, SDA pins — — 1 μAOutput Voltage Low VOL SDA pin; IOL = 2.5 mA; VDD = 3.3 V — — 0.6 VSDA pin; IOL = 1.2 mA;VDD = 1.9 V— — 0.4 VCurrentConsumptionIDD RH conversion in progress — 150 180 μATemperature conversion in progress — 90 120 μAStandby, –40 to +85 °C2 — 0.06 0.62 μAStandby, –40 to +125 °C2 — 0.06 3.8 μAPeak IDD during powerup3 — 3.5 4.0 mAPeak IDD during I2C operations4 — 3.5 4.0 mAHeater Current5 IHEAT — 3.1 to 94.2 — mANotes:1. Initiating a RH measurement will also automatically initiate a temperature measurement. The total conversion time willbe tCONV(RH) + tCONV(T).2. No conversion or I2C transaction in progress. Typical values measured at 25 °C.3. Occurs once during powerup. Duration is <5 msec.4. Occurs during I2C commands for Reset, Read/Write User Registers, Read EID, and Read Firmware Version. Duration is<100 µs when I2C clock speed is >100 kHz (>200 kHz for 2-byte commands).5. Additional current consumption when HTRE bit enabled. See Section “5.5. Heater” for more information.Si7021-A20Rev. 1.2 5Conversion Time1 tCONV 12-bit RH — 10 12ms11-bit RH — 5.8 710-bit RH — 3.7 4.58-bit RH — 2.6 3.114-bit temperature — 7 10.813-bit temperature — 4 6.212-bit temperature — 2.4 3.811-bit temperature — 1.5 2.4Powerup Time tPU From VDD ≥ 1.9 V to ready for aconversion, 25 °C— 18 25msFrom VDD ≥ 1.9 V to ready for aconversion, full temperature range— — 80After issuing a software resetcommand— 5 15Table 3. I2C Interface Specifications11.9  VDD  3.6 V; TA = –40 to +85 °C (G grade) or –40 to +125 °C (I/Y grade) unless otherwise noted.Parameter Symbol Test Condition Min Typ Max UnitHysteresis VHYS High-to-low versus low-tohigh transition0.05 x VDD ——VSCLK Frequency2 fSCL — — 400 kHzSCL High Time tSKH 0.6 — — µsSCL Low Time tSKL 1.3 — — µsStart Hold Time tSTH 0.6 — — µsStart Setup Time tSTS 0.6 — — µsNotes:1. All values are referenced to VIL and/or VIH.2. Depending on the conversion command, the Si7021 may hold the master during the conversion (clock stretch). Atabove 100 kHz SCL, the Si7021 may also hold the master briefly for user register and device ID transactions. At thehighest I2C speed of 400 kHz the stretching will be <50 µs.3. Pulses up to and including 50 ns will be suppressed.Table 2. General Specifications (Continued)1.9 < VDD < 3.6 V; TA = –40 to 85 °C (G grade) or –40 to 125 °C (I/Y grade); default conversion time unless otherwise noted.Parameter Symbol Test Condition Min Typ Max UnitNotes:1. Initiating a RH measurement will also automatically initiate a temperature measurement. The total conversion time willbe tCONV(RH) + tCONV(T).2. No conversion or I2C transaction in progress. Typical values measured at 25 °C.3. Occurs once during powerup. Duration is <5 msec.4. Occurs during I2C commands for Reset, Read/Write User Registers, Read EID, and Read Firmware Version. Duration is<100 µs when I2C clock speed is >100 kHz (>200 kHz for 2-byte commands).5. Additional current consumption when HTRE bit enabled. See Section “5.5. Heater” for more information.Si7021-A206 Rev. 1.2Figure 1. I2C Interface Timing DiagramStop Setup Time tSPS 0.6 — — µsBus Free Time tBUF Between Stop and Start 1.3 — — µsSDA Setup Time tDS 100 — — nsSDA Hold Time tDH 100 — — nsSDA Valid Time tVD;DAT From SCL low to data valid — — 0.9 µsSDA Acknowledge Valid Time tVD;ACK From SCL low to data valid — — 0.9 µsSuppressed Pulse Width3 tSPS 50 — — nsTable 3. I2C Interface Specifications1 (Continued)1.9  VDD  3.6 V; TA = –40 to +85 °C (G grade) or –40 to +125 °C (I/Y grade) unless otherwise noted.Parameter Symbol Test Condition Min Typ Max UnitNotes:1. All values are referenced to VIL and/or VIH.2. Depending on the conversion command, the Si7021 may hold the master during the conversion (clock stretch). Atabove 100 kHz SCL, the Si7021 may also hold the master briefly for user register and device ID transactions. At thehighest I2C speed of 400 kHz the stretching will be <50 µs.3. Pulses up to and including 50 ns will be suppressed.SCLD61/fSCL tSKHSDAtSKLtSTHD5 D4 D0 R/W ACKtDS tDHStart Bit Stop BittBUFtSTS tVD : ACKtSPStSPSi7021-A20Rev. 1.2 7Table 4. Humidity Sensor1.9 ≤ VDD ≤ 3.6 V; TA = 30 °C; default conversion time unless otherwise noted.Parameter Symbol Test Condition Min Typ Max UnitOperating Range1 Non-condensing 0 — 100 %RHAccuracy2, 3 0 – 80% RH — ±2 ±3 %RH80 – 100% RH See Figure 2.Repeatability/Noise 12-bit resolution — 0.025 —%RH RMS11-bit resolution — 0.05 —10-bit resolution — 0.1 —8-bit resolution — 0.2 —Response Time4 τ63%1 m/s airflow, with cover — 18 — S1 m/s airflow, without cover — 17 —Drift vs. Temperature — 0.05 — %RH/°CHysteresis — ±1 — %RHLong Term Stability3 — < 0.25 — %RH/yrNotes:1. Recommended humidity operating range is 20% to 80% RH (non-condensing) over –10 °C to 60 °C. Prolongedoperation beyond these ranges may result in a shift of sensor reading, with slow recovery time.2. Excludes hysteresis, long term drift, and certain other factors and is applicable to non-condensing environments only.See Section “4.1. Relative Humidity Sensor Accuracy” for more details.3. Drift due to aging effects at typical room conditions of 30 °C and 30% to 50% RH. May be impacted by dust, vaporizedsolvents or other contaminants, e.g., out-gassing tapes, adhesives, packaging materials, etc. See Section “4.7. LongTerm Drift/Aging” .4. Response time to a step change in RH. Time for the RH output to change by 63% of the total RH change.Si7021-A208 Rev. 1.2Figure 2. RH Accuracy at 30 °CSi7021-A20Rev. 1.2 9Figure 3. Temperature Accuracy**Note: Applies only to I and Y grade devices beyond +85 °C.Table 5. Temperature Sensor1.9 ≤ VDD ≤ 3.6 V; TA = –40 to +85 °C (G grade) or –40 to +125 °C (I/Y grade) default conversion time, unless otherwise noted.Parameter Symbol Test Condition Min Typ Max UnitOperating Range I and Y Grade –40 — +125 °CG Grade –40 — +85 °CAccuracy1 –10 °C< tA < 85 °C — ±0.3 ±0.4 °C–40 < tA < 125 °C Figure 3Repeatability/Noise 14-bit resolution — 0.01 —°C RMS13-bit resolution — 0.02 —12-bit resolution — 0.04 —11-bit resolution — 0.08 —Response Time2 τ63% Unmounted device — 0.7 — sSi7021-EB board — 5.1 —Long Term Stability —  0.01 — °C/YrNotes:1. 14b measurement resolution (default).2. Time to reach 63% of final value in response to a step change in temperature. Actual response time will varydependent on system thermal mass and air-flow.Si7021-A2010 Rev. 1.2Table 6. Thermal CharacteristicsParameter Symbol Test Condition DFN-6 UnitJunction to Air Thermal Resistance JA JEDEC 2-Layer board,No Airflow256 °C/WJunction to Air Thermal Resistance JA JEDEC 2-Layer board,1 m/s Airflow224 °C/WJunction to Air Thermal Resistance JA JEDEC 2-Layer board,2.5 m/s Airflow205 °C/WJunction to Case Thermal Resistance JC JEDEC 2-Layer board 22 °C/WJunction to Board Thermal Resistance JB JEDEC 2-Layer board 134 °C/WTable 7. Absolute Maximum Ratings1Parameter Symbol Test Condition Min Typ Max UnitAmbient temperatureunder bias–55 — 125 °CStorage Temperature2 –65 — 150 °CVoltage on I/O pins –0.3 — VDD+0.3 V VVoltage on VDD withrespect to GND–0.3 — 4.2 VESD Tolerance HBM — — 2 kVCDM — — 1.25 kVMM — — 250 VNotes:1. Absolute maximum ratings are stress ratings only, operation at or beyond these conditions is not implied and mayshorten the life of the device or alter its performance.2. Special handling considerations apply; see application note, “AN607: Si70xx Humidity Sensor Designer’s Guide”.Si7021-A20Rev. 1.2 112. Typical Application CircuitsThe primary function of the Si7021 is to measure relative humidity and temperature. Figure 4 demonstrates thetypical application circuit to achieve these functions.Figure 4. Typical Application Circuit for Relative Humidity and Temperature Measurement0.1µFVDDSCLSDA Si7021SCLSDA1.9 to 3.6V612GND10k 10k5Si7021-A2012 Rev. 1.23. Bill of MaterialsTable 8. Typical Application Circuit BOM for Relative Humidity and Temperature MeasurementReference Description Mfr Part Number ManufacturerR1 Resistor, 10 k, ±5%, 1/16 W, 0603 CR0603-16W-103JT VenkelR2 Resistor, 10 k, ±5%, 1/16 W, 0603 CR0603-16W-103JT VenkelC1 Capacitor, 0.1 µF, 16 V, X7R, 0603 C0603X7R160-104M VenkelU1 IC, Digital Temperature/humidity Sensor Si7021-A20-GM Silicon LabsSi7021-A20Rev. 1.2 134. Functional DescriptionFigure 5. Si7021 Block DiagramThe Si7021 is a digital relative humidity and temperature sensor that integrates temperature and humidity sensorelements, an analog-to-digital converter, signal processing, calibration, polynomial non-linearity correction, and anI2C interface all in a single chip. The Si7021 is individually factory-calibrated for both temperature and humidity,with the calibration data stored in on-chip non-volatile memory. This ensures that the sensor is fullyinterchangeable, with no recalibration or changes to software required. Patented use of industry-standard CMOSand low-K dielectrics as a sensor enables the Si7021 to achieve excellent long term stability and immunity tocontaminants with low drift and hysteresis. The Si7021 offers a low-power, high-accuracy, calibrated and stablesolution ideal for a wide range of temperature, humidity, and dew-point applications including medical andinstrumentation, high-reliability automotive and industrial systems, and cost-sensitive consumer electronics.While the Si7021 is largely a conventional mixed-signal CMOS integrated circuit, relative humidity sensors ingeneral and those based on capacitive sensing using polymeric dielectrics have unique application and userequirements that are not common to conventional (non-sensor) ICs. Chief among those are:The need to protect the sensor during board assembly, i.e., solder reflow, and the need to subsequentlyrehydrate the sensor.The need to protect the senor from damage or contamination during the product life-cycle.The impact of prolonged exposure to extremes of temperature and/or humidity and their potential effect onsensor accuracy.The effects of humidity sensor “memory”.Each of these items is discussed in more detail in the following sections.ADCGNDHumiditySensorControl LogicSCLSi7021TempSensor1.25VRefI2C InterfaceSDAVddCalibrationMemorySi7021-A2014 Rev. 1.24.1. Relative Humidity Sensor AccuracyTo determine the accuracy of a relative humidity sensor, it is placed in a temperature and humidity controlledchamber. The temperature is set to a convenient fixed value (typically 25–30 °C) and the relative humidity is sweptfrom 20 to 80% and back to 20% in the following steps: 20% – 40% – 60% – 80% – 80% – 60% – 40% – 20%. Ateach set-point, the chamber is allowed to settle for a period of 60 minutes before a reading is taken from thesensor. Prior to the sweep, the device is allowed to stabilize to 50%RH. The solid trace in Figure 6, “MeasuringSensor Accuracy Including Hysteresis,” shows the result of a typical sweep.Figure 6. Measuring Sensor Accuracy Including HysteresisThe RH accuracy is defined as the dotted line shown in Figure 6, which is the average of the two data points ateach relative humidity set-point. In this case, the sensor shows an accuracy of 0.25%RH. The Si7021 accuracyspecification (Table 4) includes:Unit-to-unit and lot-to-lot variationAccuracy of factory calibrationMargin for shifts that can occur during solder reflowThe accuracy specification does not include:Hysteresis (typically ±1%)Effects from long term exposure to very humid conditionsContamination of the sensor by particulates, chemicals, etc.Other aging related shifts ("Long-term stability")Variations due to temperature (see Drift vs. Temperature in Table 4). RH readings will typically vary withtemperature by less than  0.05%  C.Si7021-A20Rev. 1.2 154.2. HysteresisThe moisture absorbent film (polymeric dielectric) of the humidity sensor will carry a memory of its exposurehistory, particularly its recent or extreme exposure history. A sensor exposed to relatively low humidity will carry anegative offset relative to the factory calibration, and a sensor exposed to relatively high humidity will carry apositive offset relative to the factory calibration. This factor causes a hysteresis effect illustrated by the solid tracein Figure 6. The hysteresis value is the difference in %RH between the maximum absolute error on the decreasinghumidity ramp and the maximum absolute error on the increasing humidity ramp at a single relative humiditysetpoint and is expressed as a bipolar quantity relative to the average error (dashed trace). In the example ofFigure 6, the measurement uncertainty due to the hysteresis effect is ±1.0%RH.4.3. Prolonged Exposure to High HumidityProlonged exposure to high humidity will result in a gradual upward drift of the RH reading. The shift in sensorreading resulting from this drift will generally disappear slowly under normal ambient conditions. The amount ofshift is proportional to the magnitude of relative humidity and the length of exposure. In the case of lengthyexposure to high humidity, some of the resulting shift may persist indefinitely under typical conditions. It is generallypossible to substantially reverse this affect by baking the device (see Section “4.6. Bake/Hydrate Procedure” ).4.4. PCB Assembly4.4.1. SolderingLike most ICs, Si7021 devices are shipped from the factory vacuum-packed with an enclosed desiccant to avoidany RH accuracy drift during storage and to prevent any moisture-related issues during solder reflow. The followingguidelines should be observed during PCB assembly:Si7021 devices are compatible with standard board assembly processes. Devices should be solderedusing reflow per the recommended card reflow profile. See Section “10. PCB Land Pattern and SolderMask Design” for the recommended card reflow profile.A "no clean" solder process is recommended to minimize the need for water or solvent rinses aftersoldering. Cleaning after soldering is possible, but must be done carefully to avoid impacting theperformance of the sensor. See “AN607: Si70xx Humidity Sensor Designer’s Guide” for more informationon cleaning.It is essential that the exposed polymer sensing film be kept clean and undamaged. This can beaccomplished by careful handling and a clean, well-controlled assembly process. When in doubt or forextra protection, a heat-resistant, protective cover such as Kapton™ KPPD-1/8 polyimide tape can beinstalled during PCB assembly.Si7021s may be ordered with a factory-fitted, solder-resistant protective cover. This cover provides protectionduring PCB assembly or rework but without the time and effort required to install and remove the Kapton tape. Itcan be left in place for the lifetime of the product, preventing liquids, dust or other contaminants from coming intocontact with the polymer sensor film. See Section “8. Ordering Guide” for a list of ordering part numbers thatinclude the cover.Si7021-A2016 Rev. 1.24.4.2. RehydrationThe measured humidity value will generally shift slightly after solder reflow. A portion of this shift is permanent andis accounted for in the accuracy specifications in Table 4. After soldering, an Si7021 should be allowed toequilibrate under controlled RH conditions (room temperature, 45–55%RH) for at least 48 hours to eliminate theremainder of the shift and return the device to its specified accuracy performance.4.4.3. ReworkTo maintain the specified sensor performance, care must be taken during rework to minimize the exposure of thedevice to excessive heat and to avoid damage/contamination or a shift in the sensor reading due to liquids, solderflux, etc. Manual touch-up using a soldering iron is permissible under the following guidelines:The exposed polymer sensing film must be kept clean and undamaged. A protective cover isrecommended during any rework operation (Kapton® tape or the factory installed cover).Flux must not be allowed to contaminate the sensor; liquid flux is not recommended even with a cover inplace. Conventional lead-free solder with rosin core is acceptable for touch-up as long as a cover is inplace during the rework.If possible, avoid water or solvent rinses after touch-up. Cleaning after soldering is possible, but must bedone carefully to avoid impacting the performance of the sensor. See AN607 for more information oncleaning.Minimize the heating of the device. Soldering iron temperatures should not exceed 350 °C and the contacttime per pin should not exceed five seconds.Hot air rework is not recommended. If a device must be replaced, remove the device by hot air and soldera new part in its place by reflow following the guidelines above.*Note: All trademarks are the property of their respective owners.Figure 7. Si7021 with Factory-Installed Protective CoverSi7021-A20Rev. 1.2 174.5. Protecting the SensorBecause the sensor operates on the principal of measuring a change in capacitance, any changes to the dielectricconstant of the polymer film will be detected as a change in relative humidity. Therefore, it is important to minimizethe probability of contaminants coming into contact with the sensor. Dust and other particles as well as liquids canaffect the RH reading. It is recommended that a cover is employed in the end system that blocks contaminants butallows water vapor to pass through. Depending on the needs of the application, this can be as simple as plastic ormetallic gauze for basic protection against particulates or something more sophisticated such as a hydrophobicmembrane providing up to IP67 compliant protection.The Si7021 may be ordered with a factory-fitted, solder-resistant cover that can be left in place for the lifetime ofthe product. It is very low-profile, hydrophobic and oleophobic. See Section “8. Ordering Guide” for a list of orderingpart numbers that include the cover. A dimensioned drawing of the IC with the cover is included in Section “9.Package Outline” . Other characteristics of the cover are listed in Table 9.4.6. Bake/Hydrate ProcedureAfter exposure to extremes of temperature and/or humidity for prolonged periods, the polymer sensor film canbecome either very dry or very wet, in each case the result is either high or low relative humidity readings. Undernormal operating conditions, the induced error will diminish over time. From a very dry condition, such as aftershipment and soldering, the error will diminish over a few days at typical controlled ambient conditions, e.g.,48 hours of 45 ≤ %RH ≤ 55. However, from a very wet condition, recovery may take significantly longer. Toaccelerate recovery from a wet condition, a bake and hydrate cycle can be implemented. This operation consists ofthe following steps:Baking the sensor at 125 °C for ≥ 12 hoursHydration at 30 °C in 75% RH for ≥ 10 hoursFollowing this cycle, the sensor will return to normal operation in typical ambient conditions after a few days.4.7. Long Term Drift/AgingOver long periods of time, the sensor readings may drift due to aging of the device. Standard accelerated lifetesting of the Si7021 has resulted in the specifications for long-term drift shown in Table 4 and Table 5. Thiscontribution to the overall sensor accuracy accounts only for the long-term aging of the device in an otherwisebenign operating environment and does not include the effects of damage, contamination, or exposure to extremeenvironmental conditions.Table 9. Specifications of Protective CoverParameter ValueMaterial PTFEOperating Temperature –40 to 125 °CMaximum Reflow Temperature 260 °CIP Rating (per IEC 529) IP67Si7021-A2018 Rev. 1.25. I2C InterfaceThe Si7021 communicates with the host controller over a digital I2C interface. The 7-bit base slave address is0x40.Master I2C devices communicate with the Si7021 using a command structure. The commands are listed in the I2Ccommand table. Commands other than those documented below are undefined and should not be sent to thedevice.Table 10. I2C Slave Address ByteA6 A5 A4 A3 A2 A1 A0 R/W10000000Table 11. I2C Command TableCommand Description Command CodeMeasure Relative Humidity, Hold Master Mode 0xE5Measure Relative Humidity, No Hold Master Mode 0xF5Measure Temperature, Hold Master Mode 0xE3Measure Temperature, No Hold Master Mode 0xF3Read Temperature Value from Previous RH Measurement 0xE0Reset 0xFEWrite RH/T User Register 1 0xE6Read RH/T User Register 1 0xE7Write Heater Control Register 0x51Read Heater Control Register 0x11Read Electronic ID 1st Byte 0xFA 0x0FRead Electronic ID 2nd Byte 0xFC 0xC9Read Firmware Revision 0x84 0xB8Si7021-A20Rev. 1.2 195.1. Issuing a Measurement CommandThe measurement commands instruct the Si7021 to perform one of two possible measurements; Relative Humidityor Temperature. The procedure to issue any one of these commands is identical. While the measurement is inprogress, the option of either clock stretching (Hold Master Mode) or Not Acknowledging read requests (No HoldMaster Mode) is available to indicate to the master that the measurement is in progress; the chosen commandcode determines which mode is used.Optionally, a checksum byte can be returned from the slave for use in checking for transmission errors. Thechecksum byte will follow the least significant measurement byte if it is acknowledged by the master. Thechecksum byte is not returned if the master “not acknowledges” the least significant measurement byte. Thechecksum byte is calculated using a CRC generator polynomial of x8 + x5 + x4 + 1, with an initialization of 0x00.The checksum byte is optional after initiating an RH or temperature measurement with commands 0xE5, 0xF5,0xE3, and 0xF3. The checksum byte is required for reading the electronic ID with commands 0xFA 0x0F and 0xFC0xC9. For all other commands, the checksum byte is not supported.In the I2C sequence diagrams in the following sections, bits produced by the master and slave are color coded asshown:Table 12. I2C Bit DescriptionsName Symbol DescriptionSTART S SDA goes low while SCL high.STOP P SDA goes high while SCL high.Repeated START Sr SDA goes low while SCL high. It is allowable to generate a STOP before therepeated start. SDA can transition to high before or after SCL goes high inpreparation for generating the START.READ R Read bit = 1WRITE W Write bit = 0All other bits — SDA value must remain high or low during the entire time SCL is high (this isthe set up and hold time in Figure 1).Master SlaveSi7021-A2020 Rev. 1.2*Note: Device will NACK the slave address byte until conversion is complete.Si7021-A20Rev. 1.2 215.1.1. Measuring Relative HumidityOnce a relative humidity measurement has been made, the results of the measurement may be converted topercent relative humidity by using the following expression:Where:%RH is the measured relative humidity value in %RHRH_Code is the 16-bit word returned by the Si7021A humidity measurement will always return XXXXXX10 in the LSB field.Due to normal variations in RH accuracy of the device as described in Table 4, it is possible for the measured valueof %RH to be slightly less than 0 when the actual RH level is close to or equal to 0. Similarly, the measured valueof %RH may be slightly greater than 100 when the actual RH level is close to or equal to 100. This is expectedbehavior, and it is acceptable to limit the range of RH results to 0 to 100%RH in the host software by truncatingvalues that are slightly outside of this range.5.1.2. Measuring TemperatureEach time a relative humidity measurement is made a temperature measurement is also made for the purposes oftemperature compensation of the relative humidity measurement. If the temperature value is required, it can beread using command 0xE0; this avoids having to perform a second temperature measurement. The measuretemperature commands 0xE3 and 0xF3 will perform a temperature measurement and return the measurementvalue, command 0xE0 does not perform a measurement but returns the temperature value measured during therelative humidity measurement.The checksum output is not available with the 0xE0 command.%RH 125RH_Code65536 = --------------------------------------- – 6Sequence to read temperature value from previous RH measurementS SlaveAddress W A 0xE0 A Sr SlaveAddress R A MS ByteA LS Byte NA PSi7021-A2022 Rev. 1.2The results of the temperature measurement may be converted to temperature in degrees Celsius (°C) using thefollowing expression:Where:Temperature (°C) is the measured temperature value in °CTemp_Code is the 16-bit word returned by the Si7021A temperature measurement will always return XXXXXX00 in the LSB field.Temperature (C 175.72Temp_Code65536 = ------------------------------------------------------- – 46.85Si7021-A20Rev. 1.2 235.2. Reading and Writing User RegistersThere is one user register on the Si7021 that allows the user to set the configuration of the Si7021. The procedurefor accessing that register is described below.The checksum byte is not supported after reading a user register.5.3. Electronic Serial NumberThe Si7021 provides a serial number individualized for each device that can be read via the I2C serial interface.Two I2C commands are required to access the device memory and retrieve the complete serial number. Thecommand sequence, and format of the serial number response is described in the figure below:First access:Sequence to read a registerSSlaveAddressW ARead RegCmdA SrSlaveAddressR A Read Data NA PSequence to write a registerS Slave Address W A Write Reg Cmd A Write Data A PMaster SlaveS Slave Address W ACK 0xFA ACK 0X0F ACKS Slave Address R ACKSNA_3 ACK CRC ACK SNA_2 ACK CRC ACKSNA_1 ACK CRC ACK SNA_0 ACK CRC NACK P2nd access:S Slave Address W ACK 0xFC ACK 0XC9 ACKS Slave Address R ACKSNB_3 ACK SNB_2 ACK CRC ACKSNB_1 ACK SNB_0 ACK CRC NACK PSi7021-A2024 Rev. 1.2The format of the complete serial number is 64-bits in length, divided into 8 data bytes. The complete serial numbersequence is shown below:The SNB3 field contains the device identification to distinguish between the different Silicon Labs relative humidityand temperature devices. The value of this field maps to the following devices according to this table:0x00 or 0xFF engineering samples0x0D=13=Si70130x14=20=Si70200x15=21=Si70215.4. Firmware RevisionThe internal firmware revision can be read with the following I2C transaction:The values in this field are encoded as follows:0xFF = Firmware version 1.00x20 = Firmware version 2.0SNA_3 SNA_2 SNA_1 SNA_0 SNB_3 SNB_2 SNB_1 SNB_0SSlaveAddressW A 0x84 A 0xB8 A SSlaveAddressR A FWREV NA PSi7021-A20Rev. 1.2 255.5. HeaterThe Si7021 contains an integrated resistive heating element that may be used to raise the temperature of thesensor. This element can be used to test the sensor, to drive off condensation, or to implement dew-pointmeasurement when the Si7021 is used in conjunction with a separate temperature sensor such as another Si7021(the heater will raise the temperature of the internal temperature sensor).The heater can be activated using HTRE, bit 2 in User Register 1. Turning on the heater will reduce the tendencyof the humidity sensor to accumulate an offset due to "memory" of sustained high humidity conditions. Severaldifferent power levels are available. The various settings are adjusted using the Heater Control Register and aredescribed in the following table.Table 13. Heater Control SettingsHEATER[3:0] Typical CurrentDraw*(mA)0000 3.090001 9.180010 15.24... ...0100 27.39... ...1000 51.69... ...1111 94.20*Note: Assumes VDD = 3.3 V.Si7021-A2026 Rev. 1.26. Control Registers6.1. Register DescriptionsReset Settings = 0011_1010Table 14. Register SummaryRegister Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0User Register 1 RES1 VDDS RSVD RSVD RSVD HTRE RSVD RES0Heater ControlRegisterRSVD HEATER[3:0]Notes:1. Any register not listed here is reserved and must not be written. The result of a read operation on these bits isundefined.2. Except where noted, reserved register bits will always read back as “1,” and are not affected by write operations. Forfuture compatibiliy, it is recommended that prior to a write operation, registers should be read. Then the values readfrom the RSVD bits should be written back unchanged during the write operation.Register 1. User Register 1Bit D7 D6 D5 D4 D3 D2 D1 D0Name RES1 VDDS RSVD RSVD RSVD HTRE RSVD RES0Type R/W R R/W R/W R/W R/W R/WBit Name FunctionD7; D0 RES[1:0] Measurement Resolution:RH Temp00: 12 bit 14 bit01: 8 bit 12 bit10: 10 bit 13 bit11: 11 bit 11 bitD6 VDDS VDD Status:0: VDD OK1: VDD LowThe minimum recommended operating voltage is 1.9 V. A transition of the VDD status bit from 0 to 1 indicates that VDD isbetween 1.8 V and 1.9 V. If the VDD drops below 1.8 V, thedevice will no longer operate correctly.D5, D4, D3 RSVD ReservedD2 HTRE 1 = On-chip Heater Enable0 = On-chip Heater DisableD1 RSVD ReservedSi7021-A20Rev. 1.2 27Reset Settings = 0000_0000Register 2. Heater Control RegisterBit D7 D6 D5 D4 D3 D2 D1 D0Name RSVD Heater [3:0]Type R/W R/WBit Name FunctionD30 HEATER[3:0] D3 D2 D1 D0 Heater Current0 000 3.09 mA0 001 9.18 mA0 010 15.24 mA...0 100 27.39 mA...1 000 51.69 mA...1 1 1 1 94.20 mAD7,D6,D5,D4RSVD ReservedSi7021-A2028 Rev. 1.27. Pin Descriptions: Si7021 (Top View)Pin Name Pin # Pin DescriptionSDA 1 I2C dataGND 2 Ground. This pin is connected to ground on the circuit board through a trace. Do notconnect directly to GND plane.VDD 5 Power. This pin is connected to power on the circuit board.SCL 6 I2C clockDNC 3,4 These pins should be soldered to pads on the PCB for mechanical stability; they can beelectrically floating or tied to VDD (do not tie to GND).TGND Paddle This pad is connected to GND internally. This pad is the main thermal input to the onchip temperature sensor. The paddle should be soldered to a floating pad.DNCSCLVDD126GND 5SDA3 4 DNCSi7021-A20Rev. 1.2 298. Ordering GuideTable 15. Device Ordering GuideP/N Description Max. Accuracy Pkg OperatingRange (°C)ProtectiveCoverPackingFormatTemp RHSi7021-A20-GM Digital temperature/ humidity sensor ±0.4 °C ± 3% DFN 6 –40 to +85 °C N Cut TapeSi7021-A20-GMR Digital temperature/ humidity sensor ±0.4 °C ± 3% DFN 6 –40 to +85 °C N Tape &ReelSi7021-A20-GM1 Digital temperature/ humidity sensor ±0.4 °C ± 3% DFN 6 –40 to +85 °C Y Cut TapeSi7021-A20-GM1RDigital temperature/ humidity sensor ±0.4 °C ± 3% DFN 6 –40 to +85 °C Y Tape &ReelSi7021-A20-IM Digital temperature/ humidity sensor –industrial temp range±0.4 °C ± 3% DFN 6 –40 to +125 °C N Cut TapeSi7021-A20-IMR Digital temperature/ humidity sensor –industrial temp range±0.4 °C ± 3% DFN 6 –40 to +125 °C N Tape &ReelSi7021-A20-IM1 Digital temperature/ humidity sensor –industrial temp range±0.4 °C ± 3% DFN 6 –40 to +125 °C Y Cut TapeSi7021-A20-IM1R Digital temperature/ humidity sensor –industrial temp range±0.4 °C ± 3% DFN 6 –40 to +125 °C Y Tape &ReelSi7021-A20-YM0 Digital temperature/ humidity sensor –automotive±0.4 °C ± 3% DFN 6 –40 to +125 °C N Cut TapeSi7021-A20-YM0R Digital temperature/ humidity sensor –automotive±0.4 °C ± 3% DFN 6 –40 to +125 °C N Tape &ReelSi7021-A20-YM1 Digital temperature/ humidity sensor –automotive±0.4 °C ± 3% DFN 6 –40 to +125 °C Y Cut TapeSi7021-A20-YM1R Digital temperature/ humidity sensor –automotive±0.4 °C ± 3% DFN 6 –40 to +125 °C Y Tape &ReelNote: The “A” denotes product revision A and “20” denotes firmware version 2.0.Si7021-A2030 Rev. 1.29. Package Outline9.1. Package Outline: 3x3 6-pin DFNFigure 10. 3x3 6-pin DFNTable 16. 3x3 6-pin DFN Package Diagram DimensionsDimension Min Nom MaxA 0.70 0.75 0.80A1 0.00 0.02 0.05b 0.35 0.40 0.45D 3.00 BSC.D2 1.40 1.50 1.60e 1.00 BSC.E 3.00 BSC.E2 2.30 2.40 2.50H1 0.85 0.90 0.95H2 1.39 1.44 1.49L 0.35 0.40 0.45aaa 0.10bbb 0.10ccc 0.05ddd 0.10eee 0.05fff 0.05Notes:1. All dimensions shown are in millimeters (mm).2. Dimensioning and Tolerancing per ANSI Y14.5M-1994.Si7021-A20Rev. 1.2 319.2. Package Outline: 3x3 6-pin DFN with Protective CoverFigure 8 illustrates the package details for the Si7021 with the optional protective cover. The table below lists thevalues for the dimensions shown in the illustration.Figure 8. 3x3 6-pin DFN with Protective CoverTable 17. 3x3 6-pin DFN with Protective Cover Package Diagram DimensionsDimension Min Nom MaxA — — 1.21A1 0.00 0.02 0.05A2 0.70 0.75 0.80b 0.35 0.40 0.45D 3.00 BSC.D2 1.40 1.50 1.60e 1.00 BSC.E 3.00 BSC.E2 2.30 2.40 2.50F1 2.70 2.80 2.90F2 2.70 2.80 2.90h 0.76 0.83 0.90L 0.35 0.40 0.45R1 0.45 0.50 0.55aaa 0.10bbb 0.10ccc 0.05ddd 0.10eee 0.05Notes:1. All dimensions are shown in millimeters (mm).2. Dimensioning and Tolerancing per ANSI Y14.5M-1994.Si7021-A2032 Rev. 1.210. PCB Land Pattern and Solder Mask DesignFigure 9. Si7021 PCB Land PatternTable 18. PCB Land Pattern DimensionsSymbol mmC1 2.90E 1.00P1 1.60P2 2.50X1 0.45Y1 0.85Notes:General1. All dimensions shown are at Maximum Material Condition (MMC). Least MaterialCondition (LMC) is calculated based on a Fabrication Allowance of 0.05 mm.2. This Land Pattern Design is based on the IPC-7351 guidelines.Solder Mask Design3. All metal pads are to be non-solder mask defined (NSMD). Clearance between thesolder mask and the metal pad is to be 60 µm minimum, all the way around thepad.Stencil Design4. A stainless steel, laser-cut and electro-polished stencil with trapezoidal wallsshould be used to assure good solder paste release.5. The stencil thickness should be 0.125 mm (5 mils).6. The ratio of stencil aperture to land pad size should be 1:1 for all perimeter pins.7. A 2x1 array of 1.00 mm square openings on 1.30 mm pitch should be used for thecenter ground pad to achieve a target solder coverage of 50%.Card Assembly8. The recommended card reflow profile is per the JEDEC/IPC J-STD-020specification for Small Body Components.Si7021-A20Rev. 1.2 3311. Top Marking11.1. Si7021 Top Marking11.2. Top Marking ExplanationMark Method: LaserFont Size 0.30 mmPin 1 Indicator: Circle = 0.30 mm DiameterUpper-Left CornerLine 1 Marking: TTTT = Mfg CodeSi7021-A2034 Rev. 1.212. Additional Reference ResourcesAN607: Si70xx Humidity Sensor Designer’s GuideSi7021-A20Rev. 1.2 35DOCUMENT CHANGE LISTRevision 0.9 to Revision 0.91 Updated Table 2 on page 4.Revision 0.91 to Revision 1.0 Updated document revision to 1.0.Revision 1.0 to Revision 1.1 Updated Footnote 2 in Table 3. Updated Section “4.5. Protecting the Sensor” . Updated Table 9. Corrected a typo in the I2C sequence for no-holdmode in Section “5. I2C Interface” . Corrected a typo in Table 12. Updated Table 17 dimensions F1 and F2.Revision 1.1 to Revision 1.2 Updated diagram in "5.4. Firmware Revision" onpage 24. Updated notes in Table 18, “PCB Land PatternDimensions,” on page 32. Changed packing format from tube to cut tape for allnon-tape & reel part numbers without protective filtercovers.DisclaimerSilicon Laboratories intends to provide customers with the latest, accurate, and in-depth documentation of all peripherals and modules available for system and software implementersusing or intending to use the Silicon Laboratories products. Characterization data, available modules and peripherals, memory sizes and memory addresses refer to each specificdevice, and "Typical" parameters provided can and do vary in different applications. Application examples described herein are for illustrative purposes only. Silicon Laboratoriesreserves the right to make changes without further notice and limitation to product information, specifications, and descriptions herein, and does not give warranties as to the accuracyor completeness of the included information. Silicon Laboratories shall have no liability for the consequences of use of the information supplied herein. This document does not implyor express copyright licenses granted hereunder to design or fabricate any integrated circuits. The products must not be used within any Life Support System without the specificwritten consent of Silicon Laboratories. A "Life Support System" is any product or system intended to support or sustain life and/or health, which, if it fails, can be reasonably expectedto result in significant personal injury or death. Silicon Laboratories products are generally not intended for military applications. Silicon Laboratories products shall under nocircumstances be used in weapons of mass destruction including (but not limited to) nuclear, biological or chemical weapons, or missiles capable of delivering such weapons.Trademark InformationSilicon Laboratories Inc., Silicon Laboratories, Silicon Labs, SiLabs and the Silicon Labs logo, CMEMS®, EFM, EFM32, EFR, Energy Micro, Energy Micro logo and combinationsthereof, "the world’s most energy friendly microcontrollers", Ember®, EZLink®, EZMac®, EZRadio®, EZRadioPRO®, DSPLL®, ISOmodem ®, Precision32®, ProSLIC®, SiPHY®,USBXpress® and others are trademarks or registered trademarks of Silicon Laboratories Inc. ARM, CORTEX, Cortex-M3 and THUMB are trademarks or registered trademarks ofARM Holdings. Keil is a registered trademark of ARM Limited. All other products or brand names mentioned herein are trademarks of their respective holders.http://www.silabs.comSilicon Laboratories Inc.400 West Cesar ChavezAustin, TX 78701USASmart.Connected.Energy-FriendlyProductswww.silabs.com/productsQualitywww.silabs.com/qualitySupport and Communitycommunity.silabs.co

tone

mj8abcd

  

aliswang