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Reflective Optical Sensor SFH 7740

Reflective Optical Sensor SFH 7740

Product catalog summary

Introduction
The SFH 7740 is a compact reflective optical sensor with digital output, ideal for short-distance applications such as detecting mechanical part positions in devices like cellular phones. It operates by switching output based on the reflectivity of nearby objects.

Design and Operating Principle
Comprising an infrared LED, a phototransistor, and an ASIC, the sensor operates with low current consumption, performing measurements every 90ms. It is designed to resist ambient light interference under typical indoor conditions but may be affected by strong infrared sources.

Application Circuit
The sensor requires an external pull-up resistor and bypass capacitors to minimize noise and stabilize power. The LED current can be adjusted with an external resistor to extend the operating range or for targets with lower reflectivity.

Optical Design
The default emitter current is 10mA, suitable for 90% reflectivity targets. For greater distances or lower reflectivity, the current can be increased by measuring target reflectivity, determining the necessary current, and calculating the resistor value.

Optical Resolution
Resolution varies with distance and reflector type. Diffuse reflectors need larger spot sizes for reliable detection, while glossy reflectors enhance resolution.

General Comments
The sensor accounts for tolerances such as temperature and distance variability. A reflection ratio greater than 10 is recommended for reliable operation. Regulated power supplies should be avoided due to potential instability.

Contamination and Eye Safety
The sensor is sensitive to contamination, which can impact performance, but it is designed to be eye-safe under normal conditions.

Package and Pin Configuration
The package includes six pins with specific functions, including a test pin and an anode LED pin that should not be connected in applications.

Catalog excerpts

Absorber target Reflector Absorber target Reflector Absorber target Reflector >

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SFH 7740 ASIC Figure 3: SFH 7740 application schematic diagram, also showing a block diagram of the internals of the part. pull-up resistor bypass capacitor C bypass capacitor C > 1 2 size="-2">

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prog Reflector (min. 50mm * 50mm) Reflector (min. 50mm * 50mm) 10mm 10mm >

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Absorber target Reflector Absorber target Reflector Absorber target Reflector Absorber target Reflector Absorber target Reflector Absorber target Reflector >

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6.3 Internal timing of the SFH7740 The timing diagram > 6.2 Use of regulated power supplies 6.1 Tolerances ATTENTION: The narrow sensitivity distribution of the SFH7740 can lead to a false sense of security when attempting to use a lower reflection ratio than 10. In this case, it is possible that the device will fail under certain circumstances (e.g. varying temperature, device aging) as all design variabilities would no longer implicitly be taken into account. Figure 8: Timing diagram >

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analog signal Absorber target Reflector Absorber target Reflector Absorber target Reflector >

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Figure 10: Package drawing of the SFH 7740. > Osram Opto Semiconductors GmbH, Regensburg, is a wholly owned subsidiary of Osram GmbH, one of the worlds three largest lamp manufacturers, and offers its customers a range of solutions based on semiconductor technology for lighting, sensor and visualisation applications. The company operates facilities in Regensburg (Germany), San Josҩ (USA) and Penang (Malaysia). Further information is available at www.osram-os.com. All information contained in this document has been checked with the greatest care. OSRAM Opto Semiconductors GmbH can however, not...

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