recommended for the window opening (IR

and visible light transmissive) to get

maximum ALS also under tilted situations.

Fig.

16

illustrates

the

above

recommendations by utilizing a Ø 1.8 – 2.0

mm aperture (minimum recommended). In

case where larger airgaps are used OSRAM

recommends apertures of Ø ≥ 2.0 mm. Note

that the proximity sensor alone works also

with a smaller aperture (the PS detector

aperture is the same as the IR-LED (emitter)

but a too small aperture might impact the

detection distance).

The proposed design values do not count

for any manufacturing tolerances concerning

the placement of the component vs. cover

glass tolerances. Additionally it is worth to

mention, that the sensor works also if this

geometric guidelines are not followed.

However, this might lead - under worst case

circumstances - to some performance

reductions. It is also important to mention

that a reduced IR transmission of the cover

glass (at 850 nm) might also reduce the

maximum

switching

distance.

To

compensate for, it is recommended to either

increase the LED current or/and reduce the

PS threshold level in the relevant register.

As a rule of thumb, a 25 % one way

transmission loss at 850 nm reduces the

signal at the sensor site by a factor of 0.56

resp. the PS signal by around 13 counts and

results in a reduction of the detection range

by around a factor of 1.4 (note the pseudo-

logarithmic scale of the counts vs. detector

irradiance, see also Sec. 5.2). Please refer

to Tab. 7 for an overview.

By implementing dark cover glasses in front

of the SFH 7773 one has to take into

account

the

spectral

transmission

characteristics of the glass in order to get

the correct readings from the ALS. E.g. a

dark cover glass (90 % attenuation) means

that the measured ALS count of 100

corresponds now to 1000 lx in front of the

cover vs. 100 lx at the sensor (see also Tab.

6).

The

overall

spectral

transmission

characteristics of the cover glass might also

impact the accuracy concerning different

light sources (different attenuation of IR vs.

visible light). Please contact your local

OSRAM technical team for more support on

these issues.

For

optimized

performance

OSRAM

recommends to avoid placing the sensor

close to other components or objects as

their

reflections

might

impair

the

performance

of

the

sensor.

It

is

recommended to have black, low reflective

structures next to the sensor.

Fig. 16: Aperture design for cover glass. The above values represent an arrangement, without

considering mechanical tolerances. Performance evaluation is recommended in any case to

verify the viability of the design. Note that the sensor also performs in a less than ideal

environment (e.g. smaller apertures). For larger airgaps a larger aperture diameter is

recommended. Low reflective structures are recommended in the vicinity of the sensor for

optimized performance.

December 12, 2011

page 16 of 23