Proximity Sensor SFH 77410 pages

Proximity Sensor SFH 7741
Application note
1. Introduction
The SFH 7741 is a very small reflective
optical sensor for short distances with digital
output. With dimensions of only
3.7x3.7x1mm3, and surface-mount solder
contacts, the device may be integrated in
applications where reflective sensors have
previously not been considered. A
photograph of the part is shown in figure 1.
This device was conceived to operate as a
short- to medium-distance proximity sensor.
The typical operating range is around 30 mm
for a diffusely reflecting target with high
reflection coefficient (for example, white nonglossy paper). Based on the low mean
current consumption (45 µA) the target
applications include especially mobile
devices with touch-screens (e.g. cell
phones, PDAs, portable entertainment
devices) that must be turned off if placed
near the user’s face. It could also be used in
other proximity applications such as
contactless switches (as in Figure 2 for
example).
This application note is structured as follows:
• General description of the part’s
design and operating principle
• Application circuit recommendations
• Customization to account for optical
properties of the application
• General application comments
10/27/2010
page 1 of 7
Figure 1: Photo of the SFH 7741. Contact
pads are on the bottom side of the
package
Figure 2: The SFH 7741 may be used to
implement a contactless or proximity
switch. The presence of a hand or finger
(the target) is detected by the reflection
of light from the target.