Window Size in Housings

Window Size in Housings
Vishay Semiconductors
Window Size in Housings
In Figure 1 and 2, the minimum window size in relation to the distance between the window and the
transceiver is described.
Generally speaking, a 10 % transmission loss should
be accounted for in the design calculations so that
output power and input sensitivity requirements are
met for the system design. The external filter should
be placed squarely against the transceiver otherwise
reflection may cause emitter power loss or a decrease
in receiver sensitivity in the system.
Optically transparent window materials are available
from different sources, e.g. Bayer, GE, Rohm & Haas
(see “Source for Accessories”).
The optical window must be a minimum size of
d1 x d2 rectangular or elliptical so as not to reduce
the IrDA performance.
The following expressions apply to figures 1 to 4.
d1 = w + 2x = w + 0.54a
d2 = h + 2x = h + 0.54a
where x = a tan 15q
Dimensions of d1, d2, and a are given in mm.
The dimensions for w and h for the different packages
are as follows:
Device
Package Type
w
(mm)
h
(mm)
Baby Face (TFDUx1xx) family
9.7
4.0
2.5 mm family (as TFDUx3xx)
8.5
2.5
1.9 mm family (as TFBSx7xx)
6.2
2.0
1.6 mm family (as TFBSx6xx)
7.0
1.7
Micro Face (as TFDUx2xx)
5.7
2.7
Window
15 °
x
a
h
d2
x
15 °
18062-1
Figure 2. View from the side, example Baby Face package
15 °
w
15 °
Window
a
d1
x
x
18063-1
Figure 3. View from above, example Micro Face package
Window
15 °
w
15 °
15 °
x
Window
a
h
d2
x
d1
x
a
x
18061-1
15 °
18064-1
Figure 1. View from above, example Baby Face package
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58
Figure 4. View from the side, example Micro Face package
Document Number: 82506
Rev. 1.4, 09-Sep-05
Window Size in Housings
Vishay Semiconductors
Some recommendations to enhance robustness of
your design:
• Do not make the window larger than needed, otherwise you will unnecessarily increase the influence of ambient (sun) light.
• The larger the distance a, the better the shielding
against the ambient light.
• The outer window surface may be recessed
against the surrounding case material to protect
the window from scratches, abrasion, dust, etc.
Recessed window
avoiding scratches
Recessed transceiver
is recommended to
shield against ambient
(sun)light
±15°
Avoid vignettation but
limit the reception angle
15809
Figure 5.
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?
15 810
Figure 6. Avoid an unintentional lens effect of your window
Document Number: 82506
Rev. 1.4, 09-Sep-05
www.vishay.com
59