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rev. 1.1 6/15 copyright ? 2015 by silicon laboratories SI7020-A20 SI7020-A20 i 2 c h umidity and t emperature s ensor features applications description the si7020 i 2 c humidity and temperature sensor is a monolithic cmos ic integrating humidity and temperature sensor elements, an analog-to-digital converter, signal processing, calibration data, and an i 2 c interface. the patented use of industry-standard, low-k polymeric dielectrics for sensing humidity enables the construction of low-power, monolithi c cmos sensor ics with low drift and hysteresis, and excellent long term stability. the humidity and temperature sensors ar e factory-calibrated and the calibration data is stored in the on-chip non-volatile memory. this ensures that the sensors are fully interchangeable, with no recalibration or software changes required. the si7020 is available in a 3x3 mm dfn package and is reflow solderable. it can be used as a hardware- and software-compatible drop-in upgrade for existing rh/ temperature sensors in 3x3 mm dfn-6 packages, featuring precision sensing over a wider range and lower power cons umption. the optional factory-installed cover offers a low profile, convenient means of protecting the sensor during assembly (e.g., reflow soldering) and th roughout the life of the product, excluding liquids (hydrophobic/oleophobic) and particulates. the si7020 offers an accurate, low-power, factory-calibrated digital solution ideal for measuring humidity, dew-point, and te mperature, in applications ranging from hvac/r and asset tracking to industrial and consumer platforms. ? precision relative humidity sensor ?? 4% 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 operating range ? wide operating voltage (1.9 to 3.6 v) ? low power consumption ?? 150 a active current ?? 60 na standby current ? factory-calibrated ? i 2 c 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 and defogging ? asset and goods tracking ? mobile phones and tablets patent protected. patents pending ordering information: see page 29. pin assignments dnc scl vdd 1 2 6 5 gnd sda 3 4 dnc top view
SI7020-A20 2 rev. 1.1 functional block diagram adc gnd humidity sensor control logic scl si7020 temp sensor 1.25v ref i 2 c interface sda vdd calibration memory
SI7020-A20 rev. 1.1 3 t able of c ontents section page 1. electrical specificat ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 2. typical application ci rcuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 3. bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4. functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 4.1. relative humidity sens or accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.2. hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 4.3. prolonged exposure to high humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.4. pcb assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4.5. protecting the sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.6. bake/hydrate procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.7. long term drift/aging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5. i 2 c interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.1. issuing a measurement command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 5.2. reading and writing user registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 5.3. electronic serial number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 5.4. firmware revision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.5. heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6. control registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 6.1. register descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 7. pin descriptions: si7020 (top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 8. ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 9. package outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.1. package outline: 3x3 6- pin dfn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.2. package outline: 3x3 6-pin dfn with protective co ver . . . . . . . . . . . . . . . . . . . . . . 31 10. pcb land pattern and solder mask d esign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 11. top marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 11.1. si7020 top marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 11.2. top marking explana tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 12. additional reference resour ces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 document change list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 contact information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
SI7020-A20 4 rev. 1.1 1. electrical specifications unless otherwise specified, all mi n/max specifications apply over the recommended operating conditions. table 1. recommended operating conditions parameter symbol test condition min typ max unit power supply v dd 1.9 ? 3.6 v operating temperature t a i and y grade ?40 ? +125 c operating temperature t a g grade ?40 ? +85 c table 2. general specifications 1.9 < v dd < 3.6 v; t a = ?40 to 85 c (g grade) or ?40 to 125 c (i/y grade); default conversion ti me unless otherwise noted. parameter symbol test condition min typ max unit input voltage high v ih scl, sda pins 0.7xv dd ??v input voltage low v il scl, sda pins ? ? 0.3xv dd v input voltage range v in scl, sda pins with respect to gnd 0.0 ? v dd v input leakage i il scl, sda pins ? ? 1 a output voltage low v ol sda pin; i ol =2.5ma; v dd = 3.3 v ? ? 0.6 v sda pin; i ol =1.2ma; v dd =1.9v ??0.4v current consumption i dd rh conversion in progress ? 150 180 a temperature conversion in progress ? 90 120 a standby, ?40 to +85 c 2 ?0.060.62 a standby, ?40 to +125 c 2 ?0.063.8 a peak idd during powerup 3 ?3.54.0ma peak idd during i 2 c operations 4 ?3.54.0ma heater current 5 i heat ? 3.1 to 94.2 ? ma notes: 1. initiating a rh measurement will also automatically initiate a temperature measurement. the total conversion time will be t conv (rh) + t conv (t). 2. no conversion or i 2 c transaction in progress. typical values measured at 25 c. 3. occurs once during poweru p. duration is <5 msec. 4. occurs during i 2 c commands for reset, read/write user registers, read eid, and read firmware version. duration is <100 s when i 2 c 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.
SI7020-A20 rev. 1.1 5 conversion time 1 t conv 12-bit rh ? 10 12 ms 11-bit rh ? 5.8 7 10-bit rh ? 3.7 4.5 8-bit rh ? 2.6 3.1 14-bit temperature ? 7 10.8 13-bit temperature ? 4 6.2 12-bit temperature ? 2.4 3.8 11-bit temperature ? 1.5 2.4 powerup time t pu from v dd 1.9 v to ready for a conversion, 25 c ?1825 ms from v dd 1.9 v to ready for a conversion, full temperature range ??80 after issuing a software reset command ?515 table 2. general specifications (continued) 1.9 < v dd < 3.6 v; t a = ?40 to 85 c (g grade) or ?40 to 125 c (i/y grade); default conversion ti me unless otherwise noted. parameter symbol test condition min typ max unit notes: 1. initiating a rh measurement will also automatically initiate a temperature measurement. the total conversion time will be t conv (rh) + t conv (t). 2. no conversion or i 2 c transaction in progress. typical values measured at 25 c. 3. occurs once during poweru p. duration is <5 msec. 4. occurs during i 2 c commands for reset, read/write user registers, read eid, and read firmware version. duration is <100 s when i 2 c 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.
SI7020-A20 6 rev. 1.1 figure 1. i 2 c interface timing diagram table 3. i 2 c interface specifications 1 1.9 ? v dd ? 3.6 v; t a = ?40 to +85 c (g grade) or ?40 to +125 c (i/y grade) unless otherwise noted. parameter symbol test condition min typ max unit hysteresis v hys high-to-low versus low-to- high transition 0.05 x v dd ??v sclk frequency 2 f scl ? ? 400 khz scl high time t skh 0.6 ? ? s scl low time t skl 1.3 ? ? s start hold time t sth 0.6 ? ? s start setup time t sts 0.6 ? ? s stop setup time t sps 0.6 ? ? s bus free time t buf between stop and start 1.3 ? ? s sda setup time t ds 100 ? ? ns sda hold time t dh 100 ? ? ns sda valid time t vd;dat from scl low to data valid ? ? 0.9 s sda acknowledge valid time t vd;ack from scl low to data valid ? ? 0.9 s suppressed pulse width 3 t sps 50 ? ? ns notes: 1. all values are referenced to v il and/or v ih . 2. depending on the conversion command, the si7020 may hold t he master during the conversion (clock stretch). at above 100 khz scl, the si7020 may also hold the master brie fly for user register and device id transactions. at the highest i 2 c speed of 400 khz the stretching will be <50 s. 3. pulses up to and including 50 ns will be suppressed. scl d6 1/f scl t skh sda t skl t sth d5 d4 d0 r/w ack t ds t dh start bit stop bit t buf t sts t vd : ack t sps t sp
SI7020-A20 rev. 1.1 7 table 4. humidity sensor 1.9 v dd 3.6 v; t a = 30 c; default conversion time unless otherwise noted. parameter symbol test condition min typ max unit operating range 1 non-condensing 0 ? 100 %rh accuracy 2, 3 0 ? 80% rh ? 3 4 %rh 80 ? 100% rh see figure 2. repeatability/noise 12-bit resolution ? 0.025 ? %rh rms 11-bit resolution ? 0.05 ? 10-bit resolution ? 0.1 ? 8-bit resolution ? 0.2 ? response time 4 63% 1 m/s airflow, with cover ? 18 ? s 1 m/s airflow, without cover ? 17 ? drift vs. temperature ? 0.05 ? %rh/c hysteresis ? 1 ? %rh long term stability 3 ?< 0.25 ? %rh/yr notes: 1. recommended humidity operating range is 20% to 80% rh (non-condensing) over ?10 c to 60 c. prolonged operation beyond these ranges may result in a shift of sensor reading, with slow recovery time. 2. excludes hysteresis, long term drift, and certain other fact ors 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, vaporized solvents or other contaminants, e.g., out-gassing tapes, a dhesives, packaging materials, etc. see section ?4.7. long term 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.
SI7020-A20 8 rev. 1.1 figure 2. rh accuracy at 30 c
SI7020-A20 rev. 1.1 9 table 5. temperature sensor 1.9 v dd 3.6 v; t a = ?40 to +85 c (g grade) or ?40 to +125 c (i/y gr ade) default conversion time, unless otherwise noted. parameter symbol test condition min typ max unit operating range i and y grade ?40 ? +125 c g grade ?40 ? +85 c accuracy 1 ?10 c< t a < 85 c ? 0.3 0.4 c ?40 < t a < 125 c figure 3. repeatability/noise 14- bit resolution ? 0.01 ? c rms 13-bit resolution ? 0.02 ? 12-bit resolution ? 0.04 ? 11-bit resolution ? 0.08 ? response time 2 63% unmounted device ? 0.7 ? s si7020-eb board ? 5.1 ? s long term stability ? ? 0.01 ? c/yr notes: 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 vary dependent on system thermal mass and air-flow.
SI7020-A20 10 rev. 1.1 figure 3. temperature accuracy* *note: applies only to i and y grade devices beyond +85 c.
SI7020-A20 rev. 1.1 11 table 6. thermal characteristics parameter symbol test condition dfn-6 unit junction to air thermal resistance ? ja jedec 2-layer board, no airflow 256 c/w junction to air thermal resistance ? ja jedec 2-layer board, 1 m/s airflow 224 c/w junction to air thermal resistance ? ja jedec 2-layer board, 2.5 m/s airflow 205 c/w junction to case thermal resistance ? jc jedec 2-layer board 22 c/w junction to board thermal resistance ? jb jedec 2-layer board 134 c/w table 7. absolute maximum ratings 1 parameter symbol test condition min typ max unit ambient temperature under bias ?55 ? 125 c storage temperature 2 ?65 ? 150 c voltage on i/o pins ?0.3 ? v dd +0.3 v v voltage on vdd with respect to gnd ?0.3 ? 4.2 v esd tolerance hbm ? ? 2 kv cdm ? ? 1.25 kv mm ? ? 250 v notes: 1. absolute maximum ratings are stress ratings only, operation at or beyond these conditio ns is not implied and may shorten the life of the device or alter its performance. 2. special handling considerations apply; see application not e, ?an607: si70xx humidity sensor designer?s guide?.
SI7020-A20 12 rev. 1.1 2. typical application circuits the primary function of the si7020 is to measure relati ve humidity and temperature. figure 4 demonstrates the typical application circuit to achieve these functions. figure 4. typical application circuit for relative humidity and temperature measurement 0.1f v dd scl sda si7020 scl sda 1.9 to 3.6v 6 1 2 gnd 10k ? 10k ? 5
SI7020-A20 rev. 1.1 13 3. bill of materials table 8. typical application circuit bom for relative humidity and temperature measurement reference description mfr part number manufacturer r1 resistor, 10 k ? , 5%, 1/16 w, 0603 cr0603-16w-103jt venkel r2 resistor, 10 k ? , 5%, 1/16 w, 0603 cr0603-16w-103jt venkel c1 capacitor, 0.1 f, 16 v, x7r, 0603 c0603x7r160-104m venkel u1 ic, digital temperat ure/humidity sensor si 7020-a20-g m silicon labs
SI7020-A20 14 rev. 1.1 4. functional description figure 5. si7020 block diagram the si7020 is a digital relative humidity and temperature sensor that integrates temp erature and humidity sensor elements, an analog-to-digital converter, signal processing , calibration, polynomial non-linearity correction, and an i 2 c interface all in a single chip. the si7020 is individu ally factory-calibrated for both temperature and humidity, with the calibration data stored in on-chip non-vol atile memory. this ensures that the sensor is fully interchangeable, with no recalibration or changes to so ftware required. patented use of industry-standard cmos and low-k dielectrics as a sensor e nables the si7020 to achieve excellent long term stabilit y and immunity to contaminants with low drift and hysteresis. the si7020 offers a low-power, high-accuracy, calibrated and stable solution ideal for a wide range of temperature, humi dity, and dew-point applications including medical and instrumentation, high-reliab ility automotive and industrial systems, a nd cost-sensitive co nsumer electronics. while the si7020 is largely a conventional mixed-signal cmos integrated circuit, relative humidity sensors in general and those based on capacitive sensing using polymeric dielectrics have unique application and use requirements 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 subsequently rehydrate 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 temper ature and/or humidity and their potential effect on sensor accuracy. ?? the effects of humidity sensor ?memory?. each of these items is discussed in more detail in the following sections. adc gnd humidity sensor control logic scl si7020 temp sensor 1.25v ref i 2 c interface sda vdd calibration memory
SI7020-A20 rev. 1.1 15 4.1. relative humidi ty sensor accuracy to determine the accuracy of a relative humidity sensor, it is placed in a temperat ure and humidity controlled chamber. the temperature is set to a convenient fixed valu e (typically 25?30 c) and the relative humidity is swept from 20 to 80% and back to 20% in the following steps: 20% ? 40% ? 60% ? 80% ? 80% ? 60% ? 40% ? 20%. at each set-point, the cham ber is allowed to settle for a period of 60 minutes before a reading is taken from the sensor. prior to the sweep, the devic e is allowed to stabilize to 50%rh. the solid trace in figure 6, ?measuring sensor accuracy including hysteresis,? shows the result of a typical sweep. figure 6. measuring sensor accuracy including hysteresis the rh accuracy is defined as the dott ed line shown in figure 6, which is th e average of the two data points at each relative humidity set-point. in this case, the sensor shows an accuracy of 0.25%rh. the si7020 accuracy specification (table 4) includes: ?? unit-to-unit and lot-to-lot variation ?? accuracy of factory calibration ?? margin for shifts that can occur during solder reflow the accuracy specification does not include: ?? hysteresis (typically 1%) ?? effects from long term exposu re to very humid conditions ?? contamination of the sensor by particulates, chemicals, etc. ?? other aging related shifts ("long-term stability") ?? variations due to tem perature (see drift vs. temper ature in table 4). rh readi ngs will typically vary with temperature by less than ? 0.05% ? c .
SI7020-A20 16 rev. 1.1 4.2. hysteresis the moisture absorbent film (polymeric dielectric) of the humidity sensor will carry a memory of its exposure history, particularly its recent or extr eme exposure history. a se nsor exposed to relatively low humidity will carry a negative offset relative to the factor y calibration, and a sensor exposed to relatively hi gh humidity will carry a positive offset relative to th e factory calibration. this fact or causes a hysteresis effect illustrated by the solid trace in figure 6. the hysteresis value is the difference in %rh between the maximum absolute error on the decreasing humidity ramp and the maximum absolute error on the in creasing humidity ramp at a single relative humidity setpoint and is expressed as a bipolar quantity relative to the average error (dashed trace). in the example of figure 6, the measurement uncertainty due to the hysteresis effect is 1.0%rh. 4.3. prolonged expos ure to high humidity prolonged exposure to high humidity w ill result in a gradual upward drift of the rh reading. the shift in sensor reading resultin g from this drift will generally disappear slowly under normal am bient conditions . the amount of shift is proportional to the magnitude of relative humidi ty and the length of exposure. in the case of lengthy exposure to high humidity, some of the resulting shift may persist indefinitely under typical conditions. it is generally possible to substantially re verse this affect by baking the device (see section ?4.6. bake/hydrate procedure? ). 4.4. pcb assembly 4.4.1. soldering like most ics, si7020 devices are shipped from the fa ctory vacuum-packed with an enclosed desiccant to avoid any rh accuracy drift during storage and to prevent any moisture-related issues during solder reflow. the following guidelines should be observed during pcb assembly: ?? si7020 devices are compatible with standard board assembly processes. devices should be soldered using reflow per the recommended card reflow profile. see section ?10. pcb land pattern and solder mask design? for the recommended card reflow profile. ?? a "no clean" solder process is recommended to mini mize the need for water or solvent rinses after soldering. cleaning after soldering is possible, but must be done carefully to avoid impacting the performance of the sensor. see ?an607: si70xx humidity sensor designer?s guide? for more information on cleaning. ?? it is essential that the exposed polymer sensing film be kept clean and undamaged. this can be accomplished by careful handling and a clean, well-c ontrolled assembly process. when in doubt or for extra protection, a heat-resistant, protective cover such as kapt on? kppd-1/8 polyimide tape can be installed during pcb assembly. si7020s may be ordered with a factory-fitted, solder-resis tant protective cover. this cover provides protection during pcb assembly or rework but wit hout the time and effort required to install and remove the kapton tape. it can be left in place for the lifetime of the product, preventi ng liquids, dust or other contaminants from coming into contact with the polymer sensor film. see section ?8. ordering guide? for a list of ordering part numbers that include the cover. 4.4.2. rehydration the measured humidity value w ill generally shift slightly after solder refl ow. a portion of this shift is permanent and is accounted for in the accuracy specifications in table 4. after soldering, an si7020 should be allowed to equilibrate under contro lled rh conditions (room temperature, 45?55 %rh) for at least 48 hours to eliminate the remainder of the shift and return the device to its specified accuracy performance.
SI7020-A20 rev. 1.1 17 4.4.3. rework to maintain the specified sensor performance, care must be taken during rework to minimize the exposure of the device to excessive heat and to avoid damage/contaminati on or a shift in the sensor reading due to liquids, solder flux, etc. manual touch-up using a soldering ir on is permissible under the following guidelines: ?? the exposed polymer sensing film must be kept clean and undamaged. a protective cover is recommended 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 in place. conventional lead-free solder with rosin core is acceptable for touch-up as long as a cover is in place during the rework. ?? if possible, avoid water or solvent rinses after touch- up. cleaning after soldering is possible, but must be done carefully to avoid impacting the performance of the sensor. see ?an607: si70xx humidity sensor designer?s guide? for more information on cleaning. ?? minimize the heating of the device. soldering iron te mperatures should not exceed 350 c and the contact time per pin should not exceed five seconds. ?? hot air rework is not recommended. if a device must be replaced, remove the devi ce by hot air and solder a new part in its place by reflow following the guidelines above. *note: all trademarks are the property of their respective owners. figure 7. si7020 with factory-installed protective cover
SI7020-A20 18 rev. 1.1 4.5. protecting the sensor because the sensor operates on the pr incipal of measuring a change in capa citance, any changes to the dielectric constant of the polymer film will be detect ed as a change in relative humidity. therefore, it is important to minimize the probability of contaminants coming into contact with the sensor. dust and ot her particles as well as liquids can affect the rh reading. it is recommended that a cover is employed in the end system that blocks contaminants but allows water vapor to pass through. depending on the needs of the application, this can be as simple as plastic or metallic gauze for basic protec tion against particulates or something mo re sophisticated such as a hydrophobic membrane providing up to ip67 compliant protection. the si7020 may be ordered with a factory-fitted, solder-resis tant cover that can be left in place for the lifetime of the product. it is very low-profile, hydrophobic and oleophobic. see section ?8. ordering guide? for a list of ordering part numbers that include the cover. a dimension ed drawing of the ic with the cover is included in section ?9. package outline? . other characterist ics of the cover are listed in table 9. 4.6. bake/hydrate procedure after exposure to extremes of temperature and/or humi dity for prolonged periods, the polymer sensor film can become either very dry or very wet, in each case the result is either high or low relative humidity readings. under normal operating conditions, the induced error will diminish over time. from a very dr y condition, such as after shipment and soldering, the error will diminish over a few days at ty pical controlled ambien t conditions, e.g., 48 hours of 45 %rh 55. however, from a very wet condition, recovery may take si gnificantly longer. to accelerate recovery from a wet condition, a bake and hy drate cycle can be implemented . this operation consists of the following steps: ?? baking the sensor at 125 c for 12 hours ?? hydration at 30 c in 75% rh for 10 hours following this cycle, the sensor will return to normal operation in typical ambient conditions after a few days. 4.7. long term drift/aging over long periods of time, the sensor readings may dr ift due to aging of the devic e. standard accelerated life testing of the si7020 has resulted in the specifications for long-term drift shown in table 4 and table 5. this contribution to the overall sensor accuracy accounts only for the long-term aging of the device in an otherwise benign operating environment and does not include the effe cts of damage, contamination, or exposure to extreme environmental conditions. table 9. specifications of protective cover parameter value material ptfe operating temperature ?40 to 125 c maximum reflow temperature 260 c ip rating (per iec 529) ip67
SI7020-A20 rev. 1.1 19 5. i 2 c interface the si7020 communicates with the host controller over a digital i 2 c interface. the 7-bit base slave address is 0x40. master i 2 c devices communicate with the si7020 using a co mmand structure. the commands are listed in the i 2 c command table. commands other than those documented below are undefined and should not be sent to the device. table 10. i 2 c slave address byte a6 a5 a4 a3 a2 a1 a0 r/w 10000000 table 11. i 2 c command table command description command code measure relative humidity, hold master mode 0xe5 measure relative humidity, no hold master mode 0xf5 measure temperature, hold master mode 0xe3 measure temperature, no hold master mode 0xf3 read temperature value from previous rh measurement 0xe0 reset 0xfe write rh/t user register 1 0xe6 read rh/t user register 1 0xe7 write heater control register 0x51 read heater control register 0x11 read electronic id 1st byte 0xfa 0x0f read electronic id 2nd byte 0xfc 0xc9 read firmware revision 0x84 0xb8
SI7020-A20 20 rev. 1.1 5.1. issuing a measurement command the measurement commands instruct th e si7020 to perform one of two poss ible measurements; relative humidity or temperature. the procedure to issue any one of thes e commands is identical. while the measurement is in progress, the option of either clock stretching (hold master mode) or not acknowledging read requests (no hold master mode) is available to indicate to the master th at the measurement is in progress; the chosen command code determines which mode is used. optionally, a checksum byte can be returned from the slave for use in checking for transmission errors. the checksum byte will follow the least si gnificant measurement byte if it is acknowle dged by the master. the checksum byte is not returned if the master ?not ack nowledges? the least significant measurement byte. the checksum byte is calculated using a crc generator polynomial of x 8 + x 5 + x 4 + 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 0xfc 0xc9. for all other commands, the checksum byte is not supported. in the i 2 c sequence diagrams in the following sections, bits produced by the master and slave are color coded as shown: table 12. i 2 c bit descriptions name symbol description start 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 the repeated start. sda can transition to high before or after scl goes high in preparation for generating the start. read r read bit = 1 write w write bit = 0 all other bits ? sda value must remain high or lo w during the entire time scl is high (this is the set up and hold time in figure 1). master slave
SI7020-A20 rev. 1.1 21 note: device will nack the slave address byte until conversion is complete. sequence to perform a measurement and read back result (hold master mode) s slave address w a measure cmd a sr slave address r a clock stretch during measurement ms byte a ls byte na p a checksum na p
SI7020-A20 22 rev. 1.1 5.1.1. measuring relative humidity once a relative humidity measurement has been made, the results of the measurement may be converted to percent relative humidity by using the following expression: where: %rh is the measured relati ve humidity value in %rh rh_code is the 16-bit word returned by the si7020 a humidity measur ement 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 value of %rh to be slightly less than 0 when the actual rh level is close to or equal to 0. similarly, the measured value of %rh may be slightly greater than 100 when the actual rh level is close to or equal to 100. this is expected behavior, and it is acceptable to limit the range of rh results to 0 to 100%rh in the host software by truncating values that are slightly outside of this range. 5.1.2. measuring temperature each time a relative humidity measurement is made a te mperature measurement is also made for the purposes of temperature compensation of the relative humidity meas urement. if the temperature value is required, it can be read using command 0xe0; this avoids having to perf orm a second temperature measurement. the measure temperature commands 0xe3 and 0xf3 will perform a temperature measurement and retu rn the measurement value, command 0xe0 does not perform a measurement but returns the temperature value measured during the relative humidity measurement. the checksum output is not available with the 0xe0 command. %rh 125 ? rh_code 65536 --------------------------------------- 6 ? = sequence to read temperature value from previous rh measurement s slave address w a 0xe0 a sr slave address r a ms byte a ls byte na p
SI7020-A20 rev. 1.1 23 the results of the temperature measurement may be conver ted to temperature in degrees celsius (c) using the following expression: where: temperature (c) is the measured temperature value in c temp_code is the 16-bit word returned by the si7020 a temperature measurement will alwa ys return xxxxxx00 in the lsb field. temperature ( ? c ? 175.72 ? temp_code 65536 ------------------------------------------------------- - 46.85 ? =
SI7020-A20 24 rev. 1.1 5.2. reading and wr iting user registers there is one user register on the si7020 that allows the user to set the configuration of the si7020. the procedure for accessing that register is described below. the checksum byte is not supported after reading a user register. 5.3. electronic serial number the si7020 provides a serial number individualiz ed for each device that can be read via the i 2 c serial interface. two i 2 c commands are required to access the device memory and retrieve the complete serial number. the command sequence, and format of the serial numb er response is described in the figure below: first access: the format of the complete serial number is 64-bits in length, divided into 8 data bytes. the complete serial number sequence is shown below: the snb3 field contains the device identification to distin guish between the different s ilicon labs relative humidity and temperature devices. the value of this field maps to the following devices according to this table: sequence ? to ? read ? a ? register s slave ? address w a read ? reg ? cmd asr slave ? address r a read ? data na p sequence ? to ? write ? a ? register sslave ? address w awrite ? reg ? cmd awrite ? data ap master slave sslave ? address w ack 0xfa ack 0x0f ack sslave ? address r ack sna_3 ack crc ack sna_2 ack crc ack sna_1 ack crc ack sna_0 ack crc nack p 2nd access: sslave ? address w ack 0xfc ack 0xc9 ack sslave ? address r ack snb_3 ack snb_2 ack crc ack snb_1 ack snb_0 ack crc nack p sna_3 sna_2 sna_1 sna_0 snb_3 snb_2 snb_1 snb_0
SI7020-A20 rev. 1.1 25 0x00 or 0xff engineering samples 0x0d=13=si7013 0x14=20=si7020 0x15=21=si7021 5.4. firmware revision the internal firmware revision can be read with the following i 2 c transaction: the values in this field are encoded as follows: 0xff = firmware version 1.0 0x20 = firmware version 2.0 5.5. heater the si7020 contains an integrated resi stive heating element that may be used to raise the temperature of the sensor. this element can be used to test the sensor, to drive off condensation, or to implement dew-point measurement when the si7020 is used in conjunction with a separate temperature sensor such as another si7020 (the heater will raise th e temperature of the inte rnal temperat ure sensor). the heater can be activated using htre, bit 2 in user register 1. turning on the heater will reduce the tendency of the humidity sensor to accumulate an offset due to "memory" of sustained high humidity conditions. several different power levels are available. the various settings are adjusted using the heater control register and are described in the following table. s slave ? address w a0x84 a0xb8 a s slave ? address r a fwrev a na p table 13. heater control settings heater[3:0] typical current draw * (ma) 0000 3.09 0001 9.18 0010 15.24 ... ... 0100 27.39 ... ... 1000 51.69 ... ... 1111 94.20 *note: assumes vdd = 3.3 v.
SI7020-A20 26 rev. 1.1 6. control registers 6.1. register descriptions reset settings = 0011_1010 table 14. register summary register bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 user register 1 res1 vdds rsvd rsvd rsvd htre rsvd res0 heater control register rsvd heater[3:0] notes: 1. any register not listed here is reserved and must not be wr itten. the result of a read operation on these bits is undefined. 2. except where noted, reserved register bits will always read back as ?1,? and are not affected by write operations. for future compatibility, it is recommended that prior to a write oper ation, registers should be read. then the values read from the rsvd bits should be written back unchanged during the write operation. register 1. user register 1 bit d7 d6 d5 d4d3d2 d1 d0 name res1 vdds rsvd rsvd rsvd htre rsvd res0 type r/w r r/w r/w r/w r/w r/w bit name function d7; d0 res[1:0] measurement resolution: rh temp 00: 12 bit 14 bit 01: 8 bit 12 bit 10: 10 bit 13 bit 11: 11 bit 11 bit d6 vdds v dd status: 0: v dd ok 1: v dd low the minimum recommended operating voltage is 1.9 v. a transi- tion of the v dd status bit from 0 to 1 indicates that v dd is between 1.8 v and 1.9 v. if the v dd drops below 1.8 v, the device will no longer operate correctly. d5, d4, d3 rsvd reserved d2 htre 1 = on-chip heater enable 0 = on-chip heater disable d1 rsvd reserved
SI7020-A20 rev. 1.1 27 reset settings = 0000_0000 register 2. heater control register bitd7d6d5d4d3d2d1 d0 name rsvd heater [3:0] type r/w r/w bit name function d3:d0 heater[3:0] d3 d2 d1 d0 heater current 0000 3.09 ma 0001 9.18 ma 0010 15.24 ma ... 0100 27.39 ma ... 1000 51.69 ma ... 1 1 1 1 94.20 ma d7,d6, d5,d4 rsvd reserved
SI7020-A20 28 rev. 1.1 7. pin descriptions: si7020 (top view) pin name pin # pin description sda 1 i 2 c data gnd 2 ground. this pin is connected to ground on the circuit board through a trace. do not connect directly to gnd plane. vdd 5 power. this pin is connected to power on the circuit board. scl 6 i 2 c clock dnc 3,4 these pins should be soldered to pads on the pcb for mechanical stability; they can be electrically floating or tied to v dd (do not tie to gnd). t gnd paddle this pad is connected to gnd internally. this pad is the main thermal input to the on-chip temperature sensor . the paddle should be soldered to a floating pad. dnc scl vdd 1 2 6 5 gnd sda 3 4 dnc
SI7020-A20 rev. 1.1 29 8. ordering guide table 15. device ordering guide p/n description max. accuracy pkg operating range (c) protective cover packing format temp rh SI7020-A20-gm digital temperature/ humidity sensor 0.4 c 4% dfn 6 ?40 to +85 c n tube SI7020-A20-gmr digital temperature/ humidity sensor 0.4 c 4% dfn 6 ?40 to +85 c n tape & reel SI7020-A20-gm1 digital temperature/ humidity sensor 0.4 c 4% dfn 6 ?40 to +85 c y cut tape SI7020-A20- gm1r digital temperature/ humidity sensor 0.4 c 4% dfn 6 ?40 to +85 c y tape & reel SI7020-A20-im digital temperature/ humidity sensor ? industrial temp range 0.4 c 4% dfn 6 ?40 to +125 c n tube SI7020-A20-imr digital temperature/ humidity sensor ? industrial temp range 0.4 c 4% dfn 6 ?40 to +125 c n tape & reel SI7020-A20-im1 digital temperature/ humidity sensor ? industrial temp range 0.4 c 4% dfn 6 ?40 to +125 c y cut tape SI7020-A20-im1r digital temperature/ humidity sensor ? industrial temp range 0.4 c 4% dfn 6 ?40 to +125 c y tape & reel SI7020-A20-ym0 digital temperature/ humidity sensor ? automotive 0.4 c 4% dfn 6 ?40 to +125 c n tube SI7020-A20-ym0r digital temperature/ humidity sensor ? automotive 0.4 c 4% dfn 6 ?40 to +125 c n tape & reel SI7020-A20-ym1 digital temperature/ humidity sensor ? automotive 0.4 c 4% dfn 6 ?40 to +125 c y cut tape SI7020-A20-ym1r digital temperature/ humidity sensor ? automotive 0.4 c 4% dfn 6 ?40 to +125 c y tape & reel note: the ?a? denotes product revision a and ?20? denotes firmware version 2.0.
SI7020-A20 30 rev. 1.1 9. package outline 9.1. package outline: 3x3 6-pin dfn figure 10. 3x3 6-pin dfn table 16. 3x3 6-pin dfn package diagram dimensions dimension min nom max a 0.70 0.75 0.80 a1 0.00 0.02 0.05 b 0.35 0.40 0.45 d 3.00 bsc. d2 1.40 1.50 1.60 e 1.00 bsc. e 3.00 bsc. e2 2.30 2.40 2.50 h1 0.85 0.90 0.95 h2 1.39 1.44 1.49 l 0.35 0.40 0.45 aaa 0.10 bbb 0.10 ccc 0.05 ddd 0.10 eee 0.05 fff 0.05 notes: 1. all dimensions shown are in millimeters (mm). 2. dimensioning and tolerancing per ansi y14.5m-1994.
SI7020-A20 rev. 1.1 31 9.2. package outline: 3x3 6-pi n dfn with protective cover figure 8 illustrates the pa ckage details for the si7020 with the optional protective cover. the table below lists the values for the di mensions shown in the illustration. figure 8. 3x3 6-pin dfn with protective cover table 17. 3x3 6-pin dfn with protective cover package diagram dimensions dimension min nom max a??1.21 a1 0.00 0.02 0.05 a2 0.70 0.75 0.80 b 0.35 0.40 0.45 d 3.00 bsc. d2 1.40 1.50 1.60 e 1.00 bsc. e 3.00 bsc. e2 2.30 2.40 2.50 f1 2.70 2.80 2.90 f2 2.70 2.80 2.90 h 0.76 0.83 0.90 l 0.35 0.40 0.45 r1 0.45 0.50 0.55 aaa 0.10 bbb 0.10 ccc 0.05 ddd 0.10 eee 0.05 notes: 1. all dimensions are shown in millimeters (mm). 2. dimensioning and tolerancing per ansi y14.5m-1994.
SI7020-A20 32 rev. 1.1 10. pcb land pattern and solder mask design figure 9. si7020 pcb land pattern table 18. pcb land pattern dimensions symbol mm c1 2.90 e1.00 p1 1.60 p2 2.50 x1 0.45 y1 0.85 notes: general 1. all dimensions shown are at maximum material condition (mmc). least material condition (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 design 3. all metal pads are to be non-solder mask defined (nsmd). clearance between the solder mask and the metal pad is to be 60 m minimum, all the way around the pad. stencil design 4. a stainless steel, laser-cut and electr o-polished stencil with trapezoidal walls should 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 pa d 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 the center ground pad to achieve a target solder coverage of 50%. card assembly 8. a no-clean, type-3 solder paste is recommended. 9. the recommended card reflow profile is per the jedec/ipc j-std-020 specification for small body components. ?
SI7020-A20 rev. 1.1 33 11. top marking 11.1. si7020 top marking 11.2. top marking explanation mark method: laser font size 0.30 mm pin 1 indicator: circle = 0.30 mm diameter upper-left corner line 1 marking: tttt = mfg code
SI7020-A20 34 rev. 1.1 12. additional reference resources ?? an607: si70xx humidity sensor designer?s guide
SI7020-A20 rev. 1.1 35 d ocument c hange l ist revision 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 note 2 in table 3. ? updated section 4.5. ? updated table 9. ? corrected a typo in the i 2 c sequence for no-hold mode in section 5.1. ? corrected a typo in table 12. ? updated table 17, dimensions f1 and f2.
SI7020-A20 36 rev. 1.1 c ontact i nformation silicon laboratories inc. 400 west cesar chavez austin, tx 78701 tel: 1+(512) 416-8500 fax: 1+(512) 416-9669 toll free: 1+(877) 444-3032 please visit the silicon labs technical support web page: http://www.siliconlabs.com/suppor t/pages/contacttechnicalsupport.aspx and register to submit a technical support request. patent notice silicon labs invests in research and development to help our cust omers differentiate in the market with innovative low-power, s mall size, analog- intensive mixed-signal soluti ons. silicon labs' extensive pat ent portfolio is a testament to our unique approach and world-clas s engineering team. silicon laboratories and silicon labs are trademarks of silicon laboratories inc. other products or brandnames mentioned herein are trademarks or registered trademarks of their respective holders. the information in this document is believed to be accurate in all respects at the time of publ ication but is subject to change without notice. silicon laboratories assumes no responsibili ty for errors and omissions, and disclaim s responsibility for any consequences resu lting from the use of information included herein. a dditionally, silicon laboratorie s assumes no responsibility for the functioning of und escribed fea- tures or parameters. silicon laboratories reserves the right to make changes without further notice. silicon laboratories makes no warran- ty, representation or guarantee regarding t he suitability of its products for any par ticular purpose, nor does silicon laborato ries assume any liability arising out of the application or use of any product or circuit, and specif ically disclaims any and all liability, in cluding without limitation consequential or incidental damages . silicon laboratories products are not designed, intended, or authorized for use in applica tions intend- ed to support or sustain life, or for any other application in which the failure of the silicon laboratories product could crea te a situation where personal injury or death may occur. should buyer purchase or us e silicon laboratories products for any such unintended or unaut horized application, buyer shall indemnify and hold silicon laboratories harmle ss against all claims and damages.

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