Designing the VCNL4040 Into an Application
Application Note
www.vishay.com
Vishay Semiconductors
APPLICATION NOTE
Revision: 12-Nov-2019
4
Document Number: 84307
For technical questions, contact: sensorstechsupport@vishay.com
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
Fig. 10 - Light Holes Diameters
The diameter needs to be increased with distances between
the sensor and cover glass according to the following
calculation.
The width calculation for distances from 0 mm to 4 mm
results with this in:
a = 0.0 mm → x = 0.0 → d = 4.0 mm + 0.0 = 4.0 mm
a = 0.5 mm → x = 0.42 → d = 4.0 mm + 0.84 = 4.84 mm
a = 1.0 mm → x = 0.84 → d = 4.0 mm + 1.68 = 5.68 mm
a = 1.5 mm → x = 1.28 → d = 4.0 mm + 2.56 = 6.56 mm
a = 2.0 mm → x = 1.68 → d = 4.0 mm + 3.36 = 7.36 mm
a = 2.5 mm → x = 2.10 → d = 4.0 mm + 4.20 = 8.20 mm
a = 3.0 mm → x = 2.52 → d = 4.0 mm + 5.04 = 9.04 mm
a = 3.5 mm → x = 2.94 → d = 4.0 mm + 5.88 = 9.58 mm
a = 4.0 mm → x = 3.36 → d = 4.0 mm + 6.72 = 10.72 mm
For the two smaller holes, the diameter for the IRED can be
as small as 1.2 mm.
Fig. 11 - Window Diameters for Two Holes
Only the diameter for the photodiode needs to be increased,
as shown in the example below, with distances between the
sensor and cover glass.
The width calculation for distances from 0 mm to 1.5 mm
results in:
a = 0.0 mm → x = 0.0 → d = 1.2 mm + 0.0 = 1.2 mm
a = 0.5 mm → x = 0.42 → d = 1.2 mm + 0.84 = 2.04 mm
a = 1.0 mm → x = 0.84 → 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
The results above represent the ideal diameters of the
window. The mechanical design of the device may not allow
for these diameters.
PROXIMITY SENSOR
The main DC light sources found in the environment are
sunlight and tungsten (incandescent) bulbs. These kinds of
disturbance sources will cause a DC current in the detector
inside the sensor, which in turn will produce noise in the
receiver circuit. The negative influence of this DC light can
be reduced by optical filtering, but is reduced much more
efficiently by a so-called DC kill function. The proximity
photodiode shows its best sensitivity at about 940 nm, as
shown in fig. 12.
Fig. 12 - Spectral Sensitivity of ALS and Proximity Photodiode
The proximity sensor uses a short pulse signal of about
100 μs (PS_IT = 1T) up to 800 μs (PS_IT = 8T). The on / off
duty ratio setting now defines which repetition rate to be
used, which can be programmed from 1/40 up to 1/320.
In addition to DC light source noise, there is some reflection
of the infrared emitted light off the surfaces of the
components surrounding the VCNL4040. The distance to
the cover, proximity of surrounding components, tolerances
of the sensor, defined infrared emitter current, ambient
temperature, and type of window material used all
contribute to this reflection. The result of the reflection and
DC noise is the production of an output current on the
proximity and light sensing photodiode. This current is
converted into a count called the offset count.
In addition to the offset count, there could also be a small
noise floor during the proximity measurement, which comes
from the DC light suppression circuitry. This noise is
typically just one or two counts. Only with light sources with
strong infrared content could it be in the range from
± 5 counts to ± 10 counts.
4 ± 0.1
Ø 1.2
4 ± 0.1
d1
x
α
a
1.1
dimensions in mm
D
10
100
1000
10000
0
10
20
30
40
50
60
70
80
90
100
400 500 600 700 800 900 1000
Axis Title
1st line
2nd line
1st line
2nd line
Relative Response (%)
Wavelength (nm)
PS
ALS
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