Designing VCNL4000 into an Application

1 vishay SEMICONDUCTORSO ptoelectronicsApplication NoteDesigning VCNL4000 into an ApplicationAPPLICATION NOTE Revision: 28-Mar-111 Document Number: 83372 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT VCNL4000 is a proximity sensor with an integratedambient light sensor. It is the industry s first optical sensorto combine an infrared emitter, PIN photodiode, ambientlight sensor and signal processing in a single packagewith a 16-bit ADC for proximity measurement as well asambient light measurement. The device provides ambientlight sensing to support conventional backlight and displaybrightness adjustment, and proximity sensing for objectand motion detection. With a range of up to 20 cm ( "),this stand-alone, single component greatly simplifies theuse and design-in of a proximity sensor in consumerand industrial applications .

2 The VCNL4000 features aminiature leadless package (LLP) for surface mounting in mm x mm package with a low profile of mmdesigned specifically for the low height requirements ofsmart phone, mobile phone, digital camera, and tablet PCapplications. Through its standard I2C bus serial digitalinterface, it allows easy access to a Proximity Signal and Light intensity measurement without complex calculationsor programming. Fig. 1 - VCNL4000 Top ViewCOMPONENTS (BLOCK DIAGRAM)The major components of the VCNL4000 are shown in theblock diagram. Fig. 2 - VCNL4000 Detailed Block Diagram22296-1 InfraredEmitterProximitySensorAmbientLig htSensor121234561110987ncVDDIR AnodeIR CathodeSDASCLGNDGNDIR CathodencncncProxi PDIREDData RegisterI2 CCommand RegisterLED DriverOscillatorAmbi VCNL4000 into an ApplicationAPPLICATION NOTEA pplication Semiconductors Revision: 28-Mar-112 Document Number: 83372 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE.

3 THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT integrated infrared emitter has a peak wavelength of890 nm. It emits light that reflects off an object within 20 cmof the sensor. The infrared emitter spectrum is shown as asolid line in. The infrared emitter has a programmable drivecurrent from 10 mA to 200 mA in 10 mA steps. The infraredlight emitted is modulated at one of four user defined carrierfrequencies: kHz, kHz, MHz, PIN photodiode receives the light that is reflected offthe object and converts it to a current. It has a peaksensitivity of 890 nm, matching the peak wavelength of theemitter. It is insensitive to ambient light. It ignores the DCcomponent of light and looks for the pulsed light at one ofthe four frequencies used by the emitter. Using amodulated signal for proximity provides distinctadvantages over other sensors on the ambient light sensor receives the visible light andconverts it to a current.

4 The human eye can see light ofwavelengths from 400 nm to 700 nm with a peak of 560 s ambient light sensor closely matches this range ofsensitivity. It has peak sensitivity at 540 nm and a bandwidthfrom 430 nm to 610 Application specific integrated circuit or ASIC includesan LED driver, I2C bus interface, amplifier, integrating analogto digital converter, oscillator, and vishay s secret sauce signal processor. For proximity, it converts the current fromthe PIN photodiode to a 16-bit digital data output value. Forambient light sensing, it converts the current from theambient light detector, amplifies it and converts it to a 16-bitdigital output CONNECTIONSF igure 4 shows the pin assignments of the VCNL4000 . Onlysix of these pins need to be electrically connected while theremainder should be solder pad connections. The sixconnections include: Pin 1 - IR anode to the power supply Pin 4 - SDA to microcontroller Pin 5 - SCL to microcontroller Pin 7 - VDD to the power supply Pin 6, pin 12 - connect to ground Pin 2, pin 3 - IR cathode, no connect Pins 8 thru 11 - must not be connected Fig.

5 3 - VCNL4000 Bottom ViewThe power supply for the ASIC (VDD) and infrared emitter hasa defined range from V to V. It is best if VDD isconnected to a regulated power supply and pin 1,IR_Anode, is connected directly to the battery. Thiseliminates any influence of the high infrared emitter currentpulses on the VDD supply line. The ground pins 6 and 12 areelectrically the same. They both use the bottom metal caseand may be routed to the same stable ground plane. Thepower supply decoupling components shown in fig. 4 arestrongly recommended to isolate the sensor from otherpossible noise on the same power rail. The 100 nF capacitorshould be placed close to the VDD pin. The SCL and SDAlines need a pull-up resistor. The resistor values depend onthe Application and on the I2C bus speed. Fig. 4 - VCNL4000 Application Circuit111098765432122342 VCNL4000IR_Anode (1)VDD (7)GND (6, 12)SCL (5)I2C bus clock SCLI2C bus data SDASDA (4)10R100 nF100 nF22 FC1C2C3R110 FC422343 Designing VCNL4000 into an ApplicationAPPLICATION NOTEA pplication Semiconductors Revision: 28-Mar-113 Document Number: 83372 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE.

6 THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT DESIGN CONSIDERATIONSThe VCNL4000 is a fully integrated proximity and ambientlight sensor. Competing sensors use a discrete infraredemitter which leads to complex geometrical calculations todetermine the position of the emitter. Competing sensorsalso require a mechanical barrier between the emitter anddetectors to eliminate crosstalk; light reflecting off the insideof the window cover which can produce false proximityreadings. The VCNL4000 does not require a mechanicalbarrier. The signal processor continuously compensates forthe light reflected from windows ensuring a proper proximityreading. As a fully integrated sensor, the design process isgreatly only dimensions that the design engineer needs toconsider are the distance from the top surface of the sensorto the outside surface of the window and the size of thewindow.

7 These dimensions will determine the size of thedetection angle of half intensity of the emitter and the angle of halfsensitivity of the PIN photodiode are 55 as shown infig. 5 and fig. 6. Fig. 5 - Angle of Half Intensity of the Emitter Fig. 6 - Angle of Half Sensitivity of the PIN Photodiode Fig. 7 - Emitter and Detector Angle and DistanceFirst, the center of the sensor and center of the windowshould be aligned. With the assumption that the detectionzone is a cone shaped region with an angle of 40 , thefollowing are dimensions for the distance from the topsurface of the sensor to the outside surface of the glass, d,and the width of the window, w. The distance from thecenter of the infrared emitter to the center of the PINphotodiode is mm. Fig. 8 - Window DimensionsThe results above represent the ideal width of the mechanical design of the device may not allow for thissize.

8 The sensor will function properly in less than idealconditions. Performance testing is recommended in 20 40 60 80 - Relative Radiant Intensity22306 - Angular Displacement0 20 40 60 80 - Relative Sensitivity22308 - Angular Displacementd(mm)x( d)w( + 2 x) = 55 tan ( ) = x/d = 40 Designing VCNL4000 into an ApplicationAPPLICATION NOTEA pplication Semiconductors Revision: 28-Mar-114 Document Number: 83372 For technical questions, contact: DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENTARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT SENSORThe main DC light sources found in the environment aresunlight and tungsten (incandescent) bulbs. These kinds ofdisturbance sources will cause a DC current in the detectorinside the sensor, which in turn will produce noise in thereceiver circuit.

9 The negative influence of such DC light canbe reduced by optical filtering. Light in the visible range,400 nm to 700 nm, is completely removed by the use of anoptical cut-off filter at 800 nm. With filtering, only longerwavelength radiation above 800 nm can be detected. ThePIN photodiode therefore receives only a limited band fromthe original spectrum of these DC light sources as shown infig. 9. Fig. 9 - Spectral Sensitivity of PDAs mentioned earlier, the proximity sensor uses amodulated carrier signal on one of four user selectedfrequencies. These frequencies are far from the ballastfrequencies of fluorescent lights ensuring that the sensor isunaffected by them. The infrared emitter sends out a seriesof pulses, a burst, at the selected frequency and the PINphotodiode which features a band pass filter set to thissame frequency, receives the reflected pulses, fig.

10 10. Fig. 10 - Emitter PulsesIn addition to DC light source noise, there is some reflectionof the infrared emitted light off the surfaces which surroundthe VCNL4000 . The distance to the cover, proximity ofsurrounding components, the tolerances of the sensor, thedefined IRED current, the ambient temperature, and the typeof material used all contribute to this reflection. The result ofthe reflection and DC noise yields a total offset addition to the offset, there is also a small noise floorduring the proximity measurement which comes from thedc_light suppression circuitry. This noise is in the range from 5 counts to 20 Application should ignore this offset as well the smallnoise floor and focus on the reflected pulses by subtractingthem from the proximity readings. Fig. 11 - Proximity CalculationThe customer defines the detection algorithm used with theVCNL4000.