VISHAY SEMICONDUCTORS www.vishay.com Optical Sensors Application Note Extended Detection Range with VCNL Family of Proximity Sensors by Reinhard Schaar 1. INTRODUCTION AND BASIC OPERATION 2. IRED CONNECTION AND CIRCUITRY The VCNL4010, VCNL4020, VCNL4020X01, and VCNL3020 are proximity sensors with I2C interfaces. Each device combines an infrared emitter, PIN photodiode, and signal processing IC in a single package with a 16-bit ADC. With a range of up to 20 cm (7.9 in), these stand-alone, single-component solutions greatly simplify the use and design-in of proximity sensors in consumer and industrial applications, because no mechanical barriers are required to optically isolate the emitter from the detector. Through the standard I2C bus serial digital interface, VCNL devices allow easy access to a “Proximity Signal” measurement without complex calculations or programming. The programmable interrupt function offers wake-up functionality for the microcontroller when a proximity event occurs, which reduces processing overhead by eliminating the need for continuous polling. Some applications may require higher intensities from the emitter, because only a very weak signal is reflected from the object that needs to be detected, or the object could be at a larger distance from the sensor. The integrated infrared emitters have a peak wavelength of 890 nm. They emit light that reflects off an object within 20 cm of the sensor. To achieve this range the highest current, 200 mA, needs to be programmed (see fig. 1 below). All VCNL sensors allow the connection of a more powerful external emitter, such as an infrared emitting diode (IRED) with a lens. In this case, the internal IRED will not be powered; its anode will not be connected to the power supply. The cathode, which normally is not connected, can now be used to add an external IRED to the VCNL’s internal driver. With this configuration, all controlling and programming is the same as with the internal IRED. Fig. 2 shows the principle behind the VCNL’s operation. Instead of the internal emitter, an external IRED is connected to the VCNL internal driver and programmable current source, while its anode is connected to the power supply. GND 12 +2.5 V -5.0 V IR Anode IRED 100 000 IRED 1 Media: Kodak Gray Card IR Cathode 100 mA 2 IR Cathode 1000 200 mA 3 100 LED Driver 10 20 mA Fig. 2 - VCNL4010 Principle Operation 1 0.1 1 10 Distance to reflecng card [mm] 100 Fig. 3 and fig. 4 show the different pinning for the VCNL4010 and VCNL4020, VCNL4020X01, or VCNL3020 packages. Fig. 1 - Proximity Value vs. Distance Revision: 14-Aug-14 Document Number: 84225 1 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 APPLICATION NOTE Proximity Value (cts) max. 200 mA 10 000 Application Note www.vishay.com Vishay Semiconductors Extended Detection Range with VCNL Family of Proximity Sensors 1.7 V to 5.0 V nc IR_Anode (1) R1 R2 V DD (7) IR_Cathode (2,3) Host Micro Controller VCNL4010 GND (12,13) INT (6) GPIO SCL(5) SDA(4) I2C Bus Clock SCL I2C Bus Data SDA Fig. 3 - VCNL4010 Circuitry with an External IRED For the VCNL4010, pin 1 (IR_Anode) is not connected and the cathode of an external IRED is connected at pin 2 and pin 3. S(λ)rel - Relative Spectral Sensitivity 1.1 IRED 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 400 22307 500 600 700 800 900 1000 1100 λ - Wavelength (nm) Fig. 5 - Spectral Sensitivity of Proximity PIN Photodiode One possible IRED that could be used is the VSMF2890GX01, as featured on the sensor boards available for the VCNL4010, VCNL4020, VCNL4020X01, and VCNL3020. IRED 1.7 V to 5.0 V nc IR_Anode (1) R1 R2 V DD (5) IR_Cathode (10) VCNL4020 GND (8,9) Host Micro Controller INT (3) GPIO SCL(4) SDA(2) I2C Bus Clock SCL I2C Bus Data SDA Fig. 4 - VCNL4020, VCNL4020X01, or VCNL3020 Circuitry with an External IRED APPLICATION NOTE For the VCNL4020, VCNL4020X01, and VCNL3020 package, pin 1 (IR_Anode) is not connected and the cathode of an external IRED can be connected at pin 10. The power supply for the ASIC (VDD) has a defined range from 2.5 V to 3.6 V. The infrared emitter (internal as well as external) may be connected in the range of 2.5 V to 5.0 V. It is best if VDD is connected to a regulated power supply and IR_Anode is connected directly to the battery or power supply. This prevents any influence of the high infrared emitter current pulses on the VDD supply line. The integrated infrared emitter has a peak wavelength of 890 nm and the PIN photodiode, receiving the light that is reflected off the object and converting it to a current, has a peak sensitivity of 890 nm, perfectly matching the peak wavelength of the emitter. The chosen external IRED should have a peak wavelength of 890 nm, but down to 850 nm is also possible. At 850 nm the sensitivity of the photodiode is approximately 70 %. Revision: 14-Aug-14 Fig. 6 - VCNL4020 Sensor Board More about these sensor boards can be found here: www.vishay.com/doc?84242 3. MECHANICAL DESIGN CONSIDERATIONS The VCNL family features a 16-bit ADC. While there is crosstalk between the external emitter and the VCNL sensor when using the demo kit and software, the 16-bit ADC provides more than enough headroom to continue functioning over the entire 20 cm range. These “offset” counts may be significant, possibly up to 5000 counts, but more than 60 000 counts remain before saturating the detector. This high crosstalk can be avoided if a light barrier is placed between the IRED and sensor. A decoupling capacitor, which is needed anyway, can serve as a light barrier when placed in-between. Fig. 7 - Light Barrier in-between IRED and Sensor Document Number: 84225 2 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Extended Detection Range with VCNL Family of Proximity Sensors The emitter package in fig. 7 is called a gullwing package. Instead of this package, a reverse gullwing emitter can be used as shown in fig. 8. Because the emitter chip is below the PCB with this package, crosstalk is eliminated. Both the absolute peak value and its position within the diagram for the proximity counts versus distance to the object depend on the distance between this external IRED and the sensor. Below, the graph for the VCNL sensor board with approximately 9 mm between them is shown. Fig. 8 - Reverse Gullwing used as an External IRED Using the VSMF2890 as the external IRED provides much higher intensity than the sensor’s internal emitter. This enables object detection at distances of up to 50 cm. Of course this always depends on the material and color of the object that needs to be detected. An overview is given in table 1 at the end of this note. Using more powerful devices like the TSHF6210 would further increase the distance, and / or result in higher detection counts as indicated by the diagrams of both IREDs in fig. 9 and fig. 10. 80 Proximity Value (cts) 100 000 VSMF2890RGX01 at 200 mA 10 000 Internal IRED at 200 mA 1000 100 10 1 Media: Kodak Gray Card Med. frequency = 390 kHz 0.1 1 10 100 Distance to reflecng card [mm] Fig. 11 - Proximity Value vs. Distance for Internal and External IRED (VSMF2890GX01) For the distance from 0 mm to 3 mm, the proximity counts are lower when using an external emitter than with the internal IRED. For object distances greater than 10 mm, the proximity counts are significantly higher. For example, when the Kodak Gray card is 200 mm from the sensor, six counts were read with the VCNL’s internal IRED, but 60 counts were read with the external VSMF2890GX01. Even at a distance of 500 mm, eight counts were still measured using the external emitter. 4. APPLICATIONS IN HARSH ENVIRONMENTS For critical environments, where dust and water may cover the window for example, it is wise to have a light barrier that extends up to the cover window. To avoid possible reflection from water drops, separate windows for the emitter and detector are recommended. Fig. 9 - VSMF2890X01 and Radiant Intensity Diagram APPLICATION NOTE Separate IR windows 360 Separate chambers Fig. 12 - Emitter and Detector Totally Separated Fig. 10 - TSHF6210 and Radiant Intensity Diagram Revision: 14-Aug-14 Document Number: 84225 3 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Extended Detection Range with VCNL Family of Proximity Sensors 5. LONGER DISTANCES For even longer distances or less reflective objects, two external IREDs in series can be used. With two TSHF6210 emitters, more than 1 meter can be achieved, depending on the reflectivity of the object. +5.0 V GND 12 IRED1 max. 200 mA IRED 1 max. 200 mA If the application requires even longer detection distances, the VCNL’s internal current source will not be powerful enough. For power IREDs with operating currents up to 5 A, the VCNL can provide the current burst to an external driver, where the power IRED is connected to this driver. Possible circuitry, as well as component proposals and measurement results, are available by request by sending an e-mail to [email protected]. IR Anode IRED2 6. SOLUTION FOR DETECTION DISTANCES GREATER THAN 100 cm IR Cathode 2 IR Cathode 3 LED Driver Fig. 13 - Two IREDs in Series Connected to the VCNL4010 TABLE 1 - REFLECTION INDEX OF VARIOUS MATERIALS / COLORS Kodak Neutral Card Plastics, Glass White side (reference medium) 100 % White PVC Gray side 20 % Gray PVC Paper Blue, green, yellow, red PVC Typewriting paper 94 % Drawing card, white (Schoeller Durex) Card, light gray Envelope (beige) 90 % 100 % White polystyrene 120 % 67 % Gray partinax 100 % Fiber Glass Board Material 84 % Without copper coating Newspaper paper 97 % With copper coating on the reverse side Pergament paper 30 % to 42 % Black on White Typewriting Paper APPLICATION NOTE 11 % 40 % to 80 % White polyethylene Packing card (light brown) Drawing ink (Higgins, Pelikan, Rotring) 90 % 4 % to 6 % 9% 12 % to 19 % 30 % Glass, 1 mm thick 9% Plexiglass, 1 mm thick 10 % Metals Foil ink (Rotring) 50 % Aluminum, bright Fiber-tip pen (Edding 400) 10 % Aluminum, black anodized 60 % Fiber-tip pen, black (Stabilo) 76 % Cast aluminum, matt 45 % Photocopy 7% Copper, matt (not oxidized) 110 % Brass, bright 160 % 150 % Plotter Pen 110 % HP fiber-tip pen (0.3 mm) 84 % Gold plating, matt Black 24 needle printer (EPSON LQ-500) 28 % Textiles Ink (Pelikan) 100 % White cotton 110 % Pencil, HB 26 % Black velvet 1.5 % Note • Relative collector current (or coupling factor) of thereflex sensors for reflection on various materials. Reference is the white side of the Kodak neutral card. The sensor is positioned perpendicular to the surface. The wavelength is 950 nm. Revision: 14-Aug-14 Document Number: 84225 4 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000