Application Note

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
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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
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