PS-PD ALS-PD Oscillaor VISHAY SEMICONDUCTORS www.vishay.com Opical Sensors By Reinhard Schaar INTRODUCTION AND BASIC OPERATION The VCNL44 is a fully inegraed proximiy and ambien ligh sensor. I combines an infrared emier and phoodiode for proximiy measuremen, ambien ligh sensor, and signal processing IC in a single package wih a 16-bi ADC. The device provides ambien ligh sensing o suppor convenional backligh and display brighness auo-adjusmen, and proximiy sensing o minimize accidenal ouch inpu ha can lead o call drops and camera launch. Wih a range of up o 2 cm (7.9"), his sand-alone componen grealy simplifies he use and design-in of a proximiy sensor in consumer and indusrial applicaions, because no mechanical barriers are required o opically isolae he emier from he deecor. The VCNL44 feaures a miniaure, surface-moun 4. mm by 2.36 mm leadless package (LLP) wih a low profile of.75 mm. The device is designed specifically o mee he low heigh requiremens of smarphone, mobile phone, digial camera, and able PC applicaions. Through is sandard I 2 C bus serial digial inerface, i allows easy access o a proximiy signal and ligh inensiy measuremens. The programmable inerrup funcion offers wake-up funcionaliy for he microconroller when a proximiy even or ambien ligh change occurs, which reduces processing overhead by eliminaing he need for coninuous polling. Fig. 2 - VCNL44 Boom View COMPONENTS (BLOCK DIAGRAM) The major componens of he VCNL44 are shown in he block diagram. In addiion o he ASIC wih he ambien ligh and proximiy phoodiode, he infrared emier is also implemened. Is cahode needs o be conneced o he driver (pin 2) exernally. GND Cahode (sensor) 1 2 Driver VCNL44 DSP PS daa buffer ALS 16-bi daa buffer Oupu buffer I 2 C Inerface 8 SCL 7 SDA Fig. 1 - VCNL44 Top View Fig. 3 - VCNL44 Deailed Block Diagram The inegraed infrared emier has a peak wavelengh of 94 nm. I emis ligh ha reflecs off an objec wihin 2 cm of he sensor. An added lens helps o increase peak inensiy due o enabling a small angle of jus ± 15, as shown in fig. 4. Revision: 3-Apr-18 1 Documen Number: 8437 V DD Anode 3 4 Low pass filer IRED Temperaure sensor 6 INT 5 Cahode (IRED)
Relaive Radian Inensiy (mw/sr) Axis Tile 1. 1.9.8.7 1.6.5.4 1.3.2.1 1-9 -6-3 3 6 9 Angle (deg) Fig. 4 - Angle of Half Inensiy of he Emier The infrared emier has a programmable drive curren from 5 ma o 2 ma in eigh seps. The infrared ligh is emied in shor pulses wih a programmable duy raio from 1/4 o 1/32. The proximiy phoodiode receives he ligh ha is refleced off he objec and convers i o a curren. I has a peak sensiiviy of 94 nm, maching he peak wavelengh of he emier. The sensiiviy of he proximiy sage is also programmable by choosing from eigh differen inegraion imes. I is insensiive o ambien ligh. I ignores he DC componen of ligh and looks for he pulsed ligh a he proximiy frequency used by he emier. The ambien ligh sensor receives he visible ligh and convers i o a curren. The human eye can see ligh wih wavelenghs from 4 nm o 7 nm, wih a peak of 56 nm. Vishay s ambien ligh sensor closely maches his range of sensiiviy. I has peak sensiiviy a 54 nm and a bandwidh from 43 nm o 61 nm. The applicaion-specific inegraed circui, or ASIC, includes an LED driver, I 2 C bus inerface, amplifier, inegraed analog-o-digial converer, oscillaor, and Vishay s secre sauce signal processor. For proximiy, i convers he curren from he phoodiode o a 12-bi or 16-bi digial daa oupu value. For ambien ligh sensing, i convers he curren from he ambien ligh deecor, amplifies i, and convers i o a 16-bi digial oupu sream. PIN CONNECTIONS Fig. 3 shows he pin assignmens of he VCNL44. The connecions include: Pin 1 - connec o ground Pin 2 - IR cahode (sensor side) Pin 3 - V DD o he power supply Pin 4 - IRED anode o he power supply Pin 5 - IRED cahode (IRED side) Pin 6 - INT o microconroller Pin 7 - SDA o microconroller Pin 8 - SCL o microconroller The power supply for he ASIC (V DD ) has a defined range from 2.5 V o 3.6 V. The infrared emier can also be wihin his range. I is bes if V DD is conneced o a regulaed power supply and pin 4, he anode, is conneced direcly o he baery. This eliminaes any influence of he high infrared emier curren pulses on he V DD supply line. The power supply decoupling componens C1 and R4 (shown in fig. 5) are opional. They isolae he sensor from oher possible noise on he same power rail, bu in mos applicaions are no needed. If separae power supplies for he V DD and he infrared emier are used and here are no negaive spikes below 2.5 V, only one capacior a V DD could be used. The 1 nf capacior should be placed close o he V DD pin. The SCL and SDA, as well as he inerrup lines, need pull-up resisors. The resisor values depend on he applicaion and on he I 2 C bus speed. Common values are abou 2.2 kω o 4.7 kω for he SDA and SCL, and abou 8.2 kω o 22 kω for he inerrup lines. 2.5 V o 3.6 V R4 1R 2.5 V o 3.6 V C1 and R4 are opional for very disurbed supply Fig. 5 - VCNL44 Applicaion Circui Revision: 3-Apr-18 2 Documen Number: 8437 GND (1) C1 C2 V DD (3) 1 μf 1 nf VCNL44 ANODE (4) C3 SDA (7) 47 nf CATHODE (5) (IRED) SCL (8) CATHODE (2) (driver) INT (6) 1.8 V o 3.6 V R1 R2 R3 Hos Micro Conroller I 2 C bus daa SDA I 2 C bus clock SCL GPIO (INT)
MECHANICAL DESIGN CONSIDERATIONS The VCNL44 is a fully inegraed proximiy and ambien ligh sensor. Compeing sensors use a discree infrared emier, which leads o complex geomerical calculaions o deermine he posiion of he emier. Compeing sensors also require a mechanical barrier beween he emier and deecors o eliminae crossalk - ligh reflecing off he inside of he window cover ha can produce false proximiy readings. The VCNL44 does no require a mechanical barrier. The signal processor coninuously compensaes for he ligh refleced from windows, hus ensuring a proper proximiy reading. As a fully inegraed sensor, he design process is grealy simplified. The only dimensions ha he design engineer needs o consider are he disance from he op surface of he sensor o he ouside surface of he window, and he size of he window. These dimensions will deermine he size of he deecion zone. The angle of half inensiy of he emier is abou ± 15, as shown in fig. 6, and he sensiiviy of he phoodiodes is showing abou ± 55. Radian Inensiy (mw/sr) 1..9.8.7.6 2.5.4.3.2.1 Fig. 6 - Angle of he Half Inensiy of he Emier 4 6 8 Angle (deg) ± 15 ± 4 Fig. 8 - Emier and Deecor Angle To achieve a good ambien ligh response, he diameer of he hole wihin he cover glass should no be oo small. An angle of ± 4 will be sufficien in mos applicaions. The package drawing shows he posiion of he IRED and phoosensiive area. The +4 line should be se a he side of he phoodiode, owards pin 1. The -4 line should be se no closer han 1 mm o ha edge. The following are dimensions for he disance from he op surface of he sensor o he ouside surface of he glass, a, and he widh of he window, d. d 4. x dimensions in mm Fig. 9 - Window Dimensions for One Hole a α 1.1 D S rel - Relaive Sensiiviy 1..9.8.7.6.5.4.3.2.1 2 Fig. 7 - Angle of he Half Sensiiviy of he Phoodiode 4 6 8 ϕ - Angular Displacemen For a single round hole, he diameer should be a leas wide enough ha he openings can freely look hrough; so, abou 4 mm. Two much smaller holes are also possible. These should be a leas he same as he diameer for he IRED = 1.2 mm. Revision: 3-Apr-18 3 Documen Number: 8437
The resuls above represen he ideal diameers of he window. The mechanical design of he device may no allow for hese diameers. 4 ±.1 Fig. 1 - Ligh Holes Diameers The diameer needs o be increased wih disances beween he sensor and cover glass according o he following calculaion. The widh calculaion for disances from mm o 4 mm resuls wih his in: a =. mm x =. d = 4. mm +. = 4. mm a =.5 mm x =.42 d = 4. mm +.84 = 4.84 mm a = 1. mm x =.84 d = 4. mm + 1.68 = 5.68 mm a = 1.5 mm x = 1.28 d = 4. mm + 2.56 = 6.56 mm a = 2. mm x = 1.68 d = 4. mm + 3.36 = 7.36 mm a = 2.5 mm x = 2.1 d = 4. mm + 4.2 = 8.2 mm a = 3. mm x = 2.52 d = 4. mm + 5.4 = 9.4 mm a = 3.5 mm x = 2.94 d = 4. mm + 5.88 = 9.58 mm a = 4. mm x = 3.36 d = 4. mm + 6.72 = 1.72 mm For he wo smaller holes, he diameer for he IRED can be as small as 1.2 mm. Fig. 11 - Window Diameers for Two Holes Ø 1.2 Only he diameer for he phoodiode needs o be increased, as shown in he example below, wih disances beween he sensor and cover glass. The widh calculaion for disances from mm o 1.5 mm resuls in: a =. mm x =. d = 1.2 mm +. = 1.2 mm a =.5 mm x =.42 d = 1.2 mm +.84 = 2.4 mm a = 1. mm x =.84 d = 1.2 mm + 1.68 = 2.88 mm a = 1.5 mm x = 1.28 d = 1.2 mm + 2.56 = 3.76 mm 4 ±.1 d1 x a α 1.1 D dimensions in mm PROXIMITY SENSOR The main DC ligh sources found in he environmen are sunligh and ungsen (incandescen) bulbs. These kinds of disurbance sources will cause a DC curren in he deecor inside he sensor, which in urn will produce noise in he receiver circui. The negaive influence of his DC ligh can be reduced by opical filering, bu is reduced much more efficienly by a so-called DC kill funcion. The proximiy phoodiode shows is bes sensiiviy a abou 94 nm, as shown in fig. 12. Axis Tile 1 1 9 8 ALS 7 1 6 PS 5 4 1 3 2 1 1 4 5 6 7 8 9 1 Fig. 12 - Specral Sensiiviy of ALS and Proximiy Phoodiode The proximiy sensor uses a shor pulse signal of abou 1 μs (PS_IT = 1T) up o 8 μs (PS_IT = 8T). The on / off duy raio seing now defines which repeiion rae o be used, which can be programmed from 1/4 up o 1/32. In addiion o DC ligh source noise, here is some reflecion of he infrared emied ligh off he surfaces of he componens surrounding he VCNL44. The disance o he cover, proximiy of surrounding componens, olerances of he sensor, defined infrared emier curren, ambien emperaure, and ype of window maerial used all conribue o his reflecion. The resul of he reflecion and DC noise is he producion of an oupu curren on he proximiy and ligh sensing phoodiode. This curren is convered ino a coun called he offse coun. In addiion o he offse coun, here could also be a small noise floor during he proximiy measuremen, which comes from he DC ligh suppression circuiry. This noise is ypically jus one or wo couns. Only wih ligh sources wih srong infrared conen could i be in he range from ± 5 couns o ± 1 couns. Revision: 3-Apr-18 4 Documen Number: 8437 Relaive Response (%) Wavelengh (nm)
The applicaion should ignore his offse and small noise floor by subracing hem from he oal proximiy readings. The VCNL44 offers a subracion feaure wha auomaically does his: PS_CANC. During he developmen of he end produc, his offse coun is evaluaed and may now be wrien ino regiser 5: PS_CANC_L/M. Now he proximiy oupu daa will jus show he subracion resul of proximiy couns - offse couns. Resuls mos ofen do no need o be averaged. If an objec wih very low refleciviy or a longer range needs o be deeced, he sensor provides a regiser where he cusomer can define he number of consecuive measuremens ha he signal mus exceed before producing an inerrup. This provides sable resuls wihou requiring averaging. landing / sep. This second rap is for smooh swich-off of he LED and is execued wih very low IRED curren. The pulse lengh in oal is 2 μs. Ampliude of ha firs half is dependen on he IRED curren. The higher his curren is programmed, he higher ha pulse ampliude will be. Taking a scope picure a IR_Cahode (pin 5) will look like his:.5 V/div 125 μs 125 μs PROXIMITY CURRENT COSUMPTION Boh he ambien ligh sensor (ALS) and he proximiy sensor (PS) wihin he VCNL44 offer a separae shudown mode. Defaul values afer sar-up have hem boh disabled. The applicaion may acivae jus he one waned or boh. The VCNL44 s embedded LED driver drives he inernal IRED via he LED CATHODE pin wih a pulsed duy cycle. The IRED on / off duy raio is programmable by an I 2 C command a regiser PS_Duy. Depending on his pulse / pause raio, he overall proximiy curren consumpion can be calculaed. When higher measuremen speed or faser response ime is needed, PS_Duy may be seleced o a maximum value of 1/4, which means one measuremen will be made every 4.85 ms, bu his will hen also lead o he highes curren consumpion: PS_Duy = 1/4: peak IRED curren = 1 ma, averaged curren consumpion is 1 ma/4 = 2.5 ma. For proximiy measuremens execued jus every 4 ms: PS_Duy = 1/32 peak IRED curren = 1 ma, averaged curren consumpion is 1 ma/32 =.3125 ma. The above is always valid for he normal pulse widh of T = 1T = 125 μs, as well as for 2T, 4T, 8T, and all ohers in beween. These pulse lenghs are always doubled, resuling in 1 μs for 8T, bu he repeiion ime is also doubled, ending in a period ime of abou 32 ms. An exremely power-efficien way o execue proximiy measuremens is o apply a PS acive force mode (regiser: PS_CONF3, command: PS_AF = 1). If only a single proximiy measuremen should be done, PS_AF is se o 1 and hen PS_SD = = acive. Seing PS_Trig = 1 will hen execue jus one single measuremen. In his mode, only he I 2 C inerface is acive. In mos consumer elecronic applicaions he sensor will spend he majoriy of ime in sleep mode, i only needs o be woken up for a proximiy or ligh measuremen. In sandby mode he power consumpion is abou.2 μa. The pulse for proximiy measuremen looks o have a higher Fig. 13 - Proximiy IRED Pulse for 1T INITIALIZATION AND I 2 C TIMINGS The VCNL44 conains hireen 16-bi command codes for operaion conrol, parameer seup, and resul buffering. All regisers are accessible via I 2 C communicaion. The buil-in I 2 C inerface is compaible wih he sandard and high-speed I 2 C modes. The I 2 C H-level volage range is from 2.5 V o 3.6 V. There are only five regisers ou of he hireen ha ypically need o be defined: 1. LED_I = 5 ma o 2 ma (IRED curren) REGISTER PS_MS #4 [x4h] 2. PS_Duy = 1/4 o 1/32 (proximiy duy raio), PS_IT (proximiy inegraion ime = pulse lengh), PS_PERS (number of consecuive measuremens above / below hreshold), and PS_SD (PS power_on) REGISTER PS_CONF1 #3 [x3h] 3. ALS_IT (ALS_inegraion ime) ALS_PERS (number of consecuive measuremens above / below hreshold), and ALS_SD (ALS power_on) REGISTER ALS_CONF # [xh] 4. and 5. Definiion of he hreshold value from he number of couns he deecion of an objec should be signaled. Proximiy TOP Threshold REGISTER PS_THDL_L #6 [x6h] for he low bye and PS_THDL_H #7 [x7h] for he high bye. To define he infrared emier curren, as well as he inegraion ime (lengh of he proximiy pulsing), evaluaion ess should be performed using he leas reflecive maerial a he maximum disance specified. Revision: 3-Apr-18 5 Documen Number: 8437 4 μs/div
Fig. 13 shows he ypical digial couns oupu versus disance for hree differen emier currens for inegraion ime T1. The reflecive reference medium is he Kodak Gray card. This card shows approximaely 18 % refleciviy a 94 nm. 1 Axis Tile 1 Wih defining he duy ime (PS_Duy), he repeiion rae = he number of proximiy measuremens per second (speed of proximiy measuremens) is defined. This is possible beween 5 ms (abou 2 measuremens/s) by programming PS_Duy wih 1/4 and 4 ms (abou 25 measuremens/s) wih programming PS_Duy wih 1/32. Proximiy Value (couns) 1 1 1 5 ma 1 ma 2 ma 1 1 1/4 each 5 ms 1 1.1 1 1 1 1 Disance o Reflecing Card (mm) Fig. 16 - Proximiy Measuremens wih PS_Duy = 1/4 Fig. 14 - Proximiy Value vs. Disance for 1T This firs diagram shows he possible deecion couns wih a shor pulse of jus 1 μs. If higher deecion disances and / or objecs wih very low refleciviy should be deeced, here is he opion o exend hese proximiy pulses up o abou 8 μs for 8T. This resuls in higher couns bu may also lead o sauraion effecs for very close and very brigh objecs. This leads hen o he diagram in fig. 15 below. In order o reach he high reflecion couns of he Kodak Gray card, one has o define he proximiy range o 16 bi, oherwise he 12-bi range would jus lead o 495 couns. This is possible o selec wih: PS_HD = 1 wihin PS_CONF3 bye of command code #3. Proximiy Value (couns) 1 1 1 1 1 Axis Tile 5 ma 1 ma 2 ma 1 1.1 1 1 1 1 Disance o Reflecing Card (mm) Fig. 15 - Proximiy Value vs. Disance; PS_IT = 8T 1 1 1 1/32 each 4 ms Fig. 17 - Proximiy Measuremens wih PS_Duy = 1/32 This duy cycle also deermines how fas he applicaion reacs when an objec appears in, or is removed from, he proximiy zone. Reacion ime is also deermined by he number of couns ha mus be exceeded before an inerrup is se. This is possible o define wih proximiy persis: PS_PERS. Possible values are from 1 o 4. To define all hese regiser values, an evaluaion es should be performed. These ess can be made jus using he VCNL44 sensor board ogeher wih he SensorXplorer TM. Boh boards are available from any of Vishay s disribuors. Please see: www.vishay.com/opoelecronics/sensorxplorer. Revision: 3-Apr-18 6 Documen Number: 8437
Timing For an I 2 C bus operaing a 1 khz, o wrie or read an 8-bi bye, plus sar (or sop) and bi acknowledgemen, akes 1 μs. Togeher wih he slave address bye and he 8-bi command code bye, plus he 16-bi daa, his resuls in a oal of 4 μs. When he device is powered on, he iniializaion wih jus hese five regisers needs 5 x 4 byes (slave address, command regiser, and 16-bi daa) for a oal of 2 byes. So, 2 x 1 μs = 2 μs = 2 ms. Send Bye Wrie Command o VCNL44 1 7 1 1 8 1 8 1 8 S Slave Address Wr A Command Code A Daa Bye Low A Daa Bye High A The read-ou of 16-bi daa would ake a oal of five byes (slave address, command code, slave address wih read bi se) and 16-bi daa sen from he VCNL44. So, 5 μs: Receive Bye Read Daa from VCNL44 1 S 7 Slave Address 1 1 8 1 1 7 1 1 8 1 8 1 1 Wr A Command Code A S Slave Address Rd A Daa Bye Low A Daa Bye High A P Power Up The release of he inernal rese, he sar of he oscillaor, and he signal processor need 2.5 ms Iniialize Regisers Wrie o four regisers 16 μs - IRED curren - Proximiy duy raio - ALS inegraion ime - Proximiy inerrup TOP hreshold Once he device is powered on and he VCNL44 is iniialized, a proximiy measuremen can be aken. 1 1 P AMBIENT LIGHT SENSING Ambien ligh sensors are used o deec ligh or brighness in a manner similar o he human eye. They allow seings o be adjused auomaically in response o changing ambien ligh condiions. By urning on, urning off, or adjusing feaures, ambien ligh sensors can conserve baery power or provide exra safey by eliminaing he need for manual adjusmens. Illuminance is he measure of he inensiy of a ligh inciden on a surface and can be correlaed o he brighness perceived by he human eye. In he visible range, i is measured in unis called lux. Ligh sources wih he same lux measuremen appear o be equally brigh. In fig. 19, he incandescen ligh and sunligh have been scaled o have he same lux measuremen. In he infrared region, he inensiy of he incandescen ligh is significanly higher. A sandard silicon phoodiode is much more sensiive o infrared ligh han visible ligh. Using i o measure ambien ligh will resul in serious deviaions beween he lux measuremens of differen ligh sources and human eye percepion. Using Vishay s ambien ligh sensors will solve his problem because hey are mos sensiive o he visible par of he specrum. 1..8.6 Ambien Ligh Sensor Visible Infrared Incandescen ligh Silicon Phoodiode Asking for one forced proximiy measuremen For (acive forced, PS_IT = 8) Time o rigger [.5 x PS_IT] DC-kill ambien ligh [3 x PS_IT] Proximiy measuremen [1 x PS_IT] IRED shudown [1 x PS_IT] Read ou of he proximiy daa oal:.5t 3T 1T 1T Fig. 18 - Timing Specificaion for Acive Forced Mode 4 μs 5 μs 3 μs 1 μs 1 μs 5 μs 64 μs Fig. 19 - Relaive Specral Sensiiviy vs. Wavelengh The human eye can see ligh wih wavelenghs from 4 nm o approximaely 7 nm. The ambien ligh sensor array in he VCNL44 closely maches his range of sensiiviy and provides a digial oupu based on a 16-bi signal. Revision: 3-Apr-18 7 Documen Number: 8437.4.2 Human Eye Wavelengh (nm) 5 7 1 15. Phoopic Peak 55 nm
AMBIENT LIGHT MEASUREMENT, RESOLUTION, AND CALCULATION The ambien ligh sensors measuremen resoluion is defined o abou.1 lux/coun for he highes sensiiviy wih a 64 ms inegraion ime. The firs producion versions shown here are a bi higher in value:.15 lux/coun. The 16-bi digial resoluion is equivalen o 65 536 couns. This yields a measuremen range from.15 lux o 983 lux. For higher illuminance, shorer inegraion ime needs o be seleced, which resuls in lower resoluion. ALS RESOLUTION AND MAXIMUM DETECTION RANGE ALS_IT (7 : 6) ALS_IT INTEGRATION TIME (yp.) SENSITIVITY UNIT (lux/sep) MAXIMUM DETECTION RANGE UNIT (lux) (, ) 8 ms.12 7864 (, 1) 16 ms.6 3932 (1, ) 32 ms.3 1966 (1, 1) 64 ms.15 983 The sensiiviy curve below shows he behavior of his ALS phoodiode. Normalized Oupu 1.2 1..8.6.4.2 Axis Tile 1 4 5 6 7 8 9 1 Wavelengh (nm) Fig. 2 - Relaive Specral Sensiiviy vs. Wavelengh Besides he ALS, a whie channel is also available. 1 1 1 1 4 5 6 7 8 9 1 Wavelengh (nm) Fig. 21 - Relaive Specral Sensiiviy vs. Wavelengh (Whie Channel) Wih he help of his whie channel, more informaion can be deermined, e.g. he kind of ligh source. AMBIENT LIGHT SENSOR CURRENT CONSUMPTION The ambien ligh sensor can operae wih four selecable inegraion imes from 8 ms o 64 ms. During ALS measuremens, he device consumes approximaely 26 μa. AMBIENT LIGHT INITIALIZATION AND I 2 C INTERFACE For ambien ligh sensing, only he low bye of command code # needs o be iniialized: ALS_SD (bi = = ALS Power_on) ALS_INT_EN (bi 1 = 1 = ALS inerrup enable) ALS_PERS (bi 2, 3: no. of inerrup persisence) ALS_IT (bi 6, 7: inegraion ime) The rae for self-imed measuremens is dependen on he inegraion ime. For unknown brighness condiions, i should always be sared wih he shores inegraion ime. This avoids possible overload / sauraion. Only if ambien ligh resul regiser values are very low, e.g. no conen wihin he high bye of he 16-bi regiser (#9), should he nex more sensiive inegraion ime be used. Calculaing he available lux level is done by muliplying he ambien ligh resul value from regiser 9 (L and H bye) wih he inegraion ime / resoluion. Example: inegraion ime is a 8 ms and x9h and x9l show 111 and 11111, expressed in decimals: 21 622 couns leading o 21 622 x.12 o 2595 lx. Revision: 3-Apr-18 8 Documen Number: 8437 Normalized Oupu 1..9.8.7.6.5.4.3.2.1 Axis Tile 1 1 1
Wihin he ready-made applicaion, his facor should be fine-uned, as cover glass and he size of he opening will also impac he resul. Inerrup The VCNL44 feaures a very inelligen inerrup funcion. The inerrup funcion enables he sensor o work independenly unil a predefined proximiy or ambien ligh even or hreshold occurs. I hen ses an inerrup which requires he microconroller o awaken. This helps cusomers reduce heir sofware effor, and reduces power consumpion by eliminaing polling communicaion raffic beween he sensor and microconroller. The inerrup pin, pin 6, of he VCNL44 should be conneced o a dedicaed GPIO of he conroller. A pull-up resisor is added o he same power supply ha he conroller is conneced o. This INT pull-up resisor may be in he range of 8.2 kω o 1 kω. The evens ha can generae an inerrup include: 1. A lower and an upper hreshold for he proximiy value can be defined. If he proximiy value falls below he lower limi or exceeds he upper limi, an inerrup even will be generaed. In his case, an inerrup flag bi in he read-ou regiser xb will be se and he inerrup pad of he VCNL will be pulled o low by an open drain pull-down circui. In order o eliminae false riggering of he inerrup by noise or disurbances, i is possible o define he number of consecuive measuremens ha have o occur before he inerrup is riggered. 2. A lower and an upper hreshold for he ambien ligh value can be defined. If he ambien ligh value falls below he lower limi or exceeds he upper limi, an inerrup even will be generaed. There are wo ses of high and low hreshold regisers, so boh hresholds for proximiy and ambien ligh can be observed in parallel. Beside his normal inerrup mode, an auomaic mode is also available, which is called he logic oupu mode. This mode auomaically pulls he inerrup pin low when an objec exceeds he programmed upper hreshold and also reses i if he lower hreshold is exceeded. So no acions from he conroller are needed if, for example, a smarphone is held close o an ear bu quickly aken away (e.g. for a shor look a he display). Applicaion Example The following example will demonsrae he ease of using he VCNL44 sensor. Cusomers are srongly encouraged o purchase a SensorXplorer and VCNL44 sensor board from any lised disribuer: www.vishay.com/opoelecronics/sensorxplorer. Offse During developmen, he applicaion-specific offse couns for he sensor were deermined. As previously menioned, he offse coun is affeced by he componens surrounding he VCNL44, he window or cover being used, he disance from he sensor o he cover, and emier inensiy, which is conrolled by he forward curren. In he following example, wih a cover over he sensor and seing he emier curren o 1 ma, he offse couns are 54 couns (fig. 22). Offse couns vary by applicaion and can be anywhere from couns o several housand couns. I is imporan o noe ha he offse coun may change slighly over ime due o, for example, he window becoming scrached or diry, or being exposed o high-emperaure changes. If possible, he offse value should occasionally be checked and, if necessary, modified. 16 bi value FFFF (65 535) Inerrup flags Time o A: Power Up inerrup hreshold = inerrup hreshold = FFFF (65 535) Inerrup flag =, inerrup line high High limi and low limi flags = Revision: 3-Apr-18 9 Documen Number: 8437 Offse: 21Ch (54) A Fig. 22 Power Up As menioned, here are four variables for proximiy measuremen ha need o be se in he regiser when he sensor is powered up: he emier curren, he number of occurrences ha mus exceed a hreshold o generae an inerrup, he hreshold values, and he number of proximiy measuremens per second. The sensor should deec skin a a disance of 5 cm. Developmen esing deermined ha a curren of 1 ma produces adequae couns for deecion. The proximiy measuremen rae is se so ha abou 1 measuremens are done wihin a second and he number of occurrences o rigger an inerrup is se o four. Based on developmen esing, wih a hand or skin approximaely 5 cm above he window cover, he resuling oal coun is 55. This will be used as he upper hreshold (high hreshold). For smarphone applicaions i would be ypical o iniially se his op hreshold and a lower hreshold (boom hreshold). This is needed o indicae he removal of he phone from he user s ear. The measured couns wihou any addiional objec close by will be around his offse coun value, always below he lower hreshold value, as shown in fig. 23.
16 bi value FFFF (65 535) hreshold: 226h (55) hreshold: 221h (545) (OC:54) Inerrup flags A Time A: μc Sleep inerrup hreshold = 55 inerrup hreshold = 545 PS_INT (1 : 1) = Inerrup flag =, inerrup line high High limi (close) and low limi (away) flags = Fig. 23 By seing he number of occurences before generaing an inerrup o 4, a single proximiy value above or below he hresholds will have no effec, as shown in fig. 24. 16 bi value FFFF (65 535) hreshold: 226h (55) hreshold: 221h (545) (OC:54) Inerrup flags A Fig. 24 hreshold hreshold Time B: Single Even Above Threshold inerrup hreshold = 545 inerrup hreshold = 55 Inerrup flags =, inerrup line high B hreshold hreshold A smarphone applicaion will use a proximiy sensor o deec when he phone is brough o he user s ear and disable he ouchscreen and urn off he backligh. For oher applicaions, such as auomaic dispensing, he soap or owel will be dispensed. 16 bi value FFFF (65 535) hreshold: 226h (55) hreshold: 221h (545) (OC:54) Inerrup flags Time C: Threshold Exceeded Time D: Number of Occurence > 4 Inerrup is generaed Inerrup flag prox_h_op is se o 1 Revision: 3-Apr-18 1 Documen Number: 8437 A B Fig. 25 In smarphone applicaions, he boom hreshold will also be programmed and wais for an inerrup signal. The prox_hreshold_boom should be se o 1 now and he prox_hreshold_op cleared by enering a 1 again, since he phone is already nex o he user s ear. A lower hreshold will occur when he phone call is complee and he phone is brough away from he user s ear, and he backligh and ouchscreen will be urned back on. For his example, he upper hreshold will only be se o 56 couns. The lower hreshold is se o 545 couns; a value ha is higher han he offse bu low enough o indicae he removal of he phone from he user s ear. 16 bi value FFFF (65 535) hreshold: 226h (55) hreshold: 221h (545) (OC:54) Inerrup flags A B Fig. 26 C D hreshold hreshold Time F: Call Ends Inerrup is generaed Inerrup flag prox_h_boom is se o 1 Inerrup line goes low C D E F hreshold hreshold
16 bi value FFFF (65 535) hreshold: 226h (55) hreshold: 221h (545) (OC:54) Time E: μc Awake, Threshold Rese Inerrup is cleared Inerrup flag prox_h_op programmed o 1 inerrup hreshold = 545 Inerrup flag prox_h_boom programmed o 1 High limi and low limi flags = hreshold hreshold Inerrup flags A B C D E Fig. 27 Some measuremens and feaures are shown wih he demo ool and demo sofware wih a cover glass a abou a 5 mm disance. 1. Proximiy se-up wih 2T wide pulses, 1 ma emier curren, and a duy cycle of 1/8, which resuls in abou 1 measuremens per second. Revision: 3-Apr-18 11 Documen Number: 8437
2. If a hand or skin now comes as close as 5 cm, hese 54 couns rise up o more han 55 couns. 3. Here he hresholds are programmed as 55 for he upper and 545 for he lower. To see hese, boh Show buons are acivaed. The presence of an objec should only be recognized when four consecuive measuremens are above ha hreshold. Revision: 3-Apr-18 12 Documen Number: 8437
4. Jus one or wo measuremens above he hreshold will no acivae he inerrup. 5. Wih more han four measuremens above he hreshold, however, he inerrup is pulled low, as indicaed by he red LED on he demo board and he red ligh: In Pin Triggered PS. Revision: 3-Apr-18 13 Documen Number: 8437
6. The cancellaion feaure is used below. The before seen offse couns are subraced. To do so, he value of 54 is enered for regiser number 5 = Prox_Cancellaion. 7. The before seen measured proximiy resul daa of 541 is now 541-54 = 1. Also, he hresholds are now 54 couns lower. The higher hreshold is 1 and lower is jus 5. Revision: 3-Apr-18 14 Documen Number: 8437
If one chooses logic mode now and redefines he high hreshold o 1 and low hreshold as 5... he inerrup will indicae he rise above he upper hreshold and will also auomaically be cleared when i falls below he lower hreshold. One special feaure for faser proximiy measuremens is also implemened, which is called smar persis. This feaure reduces he oal reacion ime unil he inerrup is se o acive, alhough four consecuive measuremens should be above (or below) he defined hreshold for safe acknowledgmen. Revision: 3-Apr-18 15 Documen Number: 8437
Wihou smar persis, bu wih programmed his above he defined hreshold se o four, i will ake four imes he ime of PS_Duy. Wih PS_Duy se o 1/32 his would be 4 x 38.4 ms. 4 his needed 4 his needed: oal ime = 115.2 ms... where wihou smar persis i akes his four imes of being above he defined hreshold before he inerrup goes low. Wih smar persis acivaed (bi 4 of PS_CONF3): REGISTER: PS_CONF3 DESCRIPTION REGISTER: PS_CONF3 COMMAND CODE: x4_l (x4 DATA BYTE LOW) Command Bi Descripion Reserved 7 Reserved 6 : 5 ( : ) PS_SMART_PERS 4 = disable; 1 = enable PS smar persisence or wihin he demo-ool: The oal needed ime is reduced o jus one ime of 38.5 ms, followed by hree imes of jus 1.3 ms beween he nex hree measuremens, for a oal of 39.7 ms. 4 his needed: oal ime = 38.4 ms + 3 x 1.3 ms = 39.7 ms Wih smar persis enabled, he inerrup is se afer four measuremens shorly afer each oher... Remark: Wih smar persis enabled, here will always be four pulses shorly afer each oher, wheher PS_PERS is se o 2, 3, or 4. Revision: 3-Apr-18 16 Documen Number: 8437