Si1120-A-GM Silicon Laboratories Inc, Si1120-A-GM Datasheet - Page 8

• Manufacturer Part Number: Si1120-A-GM
• Description: Industrial Optical Sensors Proximity/Ambient Light Snsr w/PWM Out
• Manufacturer: Silicon Laboratories Inc
• Type: Ambient Light Sensor with Analog Outputr

Specifications of Si1120-A-GM

• Product: Integrated Ambient Light and Proximity Sensor
• Output Type: Analog - Voltage
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Si 1120
2.3. Proximity Modes
In proximity mode, an LED sends light pulses that are reflected from the target to a photodiode and processed by
the Si1120’s analog circuitry. Light reflected from a proximate object is detected by the receiver, and the Si1120
converts the light signal into a pulse at the PRX output of a duration proportional to the amount of reflected light.
The LED is turned off at the trailing (rising) edge of the PRX pulse. The detection cycle may be aborted before the
end of the PRX pulse by bringing STX low. This allows the system designer to limit the maximum LED “on” time in
applications where high reflectivity periods are not of interest, thus saving power and minimizing the LED duty
cycle. Aborting the detection cycle at a set time also enables fast threshold comparison by sampling the state of the
PRX output at the trailing (falling) edge of the STX input. An active (low) PRX output when STX falls means that an
object is within the detection range. Forcing a shorter detection cycle also allows a faster proximity measurement
rate thus allowing more samples to be averaged for an overall increase in the signal-to-noise ratio.
For long-range detection, PRX400 mode is selected. For short-range detection, PRX50 mode is selected. PRX50H
mode is typically used in short-range, single-optical-port applications where the internal optical reflection level is
high. The greater reflectance range combined with a lower LED power prevents internal reflections from saturating
the receiver circuit.
The offset calibration mode works the same way as the other proximity modes but without turning on the LED. This
allows precise measurement of the environment and Si1120 internal offsets without any LED light being reflected.
The offset calibration mode also allows compensation of drifts due to supply and temperature changes.
Figure 3. Proximity Mode Timing Diagram
Figure 4. Proximity Mode Timing Diagram (Aborted Cycle)
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Rev. 1.0