Si1102-A-GMR Silicon Laboratories Inc, Si1102-A-GMR Datasheet - Page 7

• Manufacturer Part Number: Si1102-A-GMR
• Description: Proximity Sensors Optical Proximity Detector
• Manufacturer: Silicon Laboratories Inc
• Series: -r

Specifications of Si1102-A-GMR

• Maximum Operating Temperature: + 85 C
• Supply Voltage: 5.25 V
• Supply Current: 10 uA
• Operating Supply Voltage: 2 V to 5.5 V
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 25 C
• Maximum Output Current: 100 mA
• Featured Product: QuickSenseâ„¢ Portfolio
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 336-1826 - BOARD EVAL FOR SI1102

Si1102
3. Application Information
3.1. Theory of Operation
The Si1102 is an active optical reflectance proximity detector with a simple on/off digital output whose state is
based upon the comparison of reflected light against a set threshold. An LED sends light pulses whose reflections
reach a photodiode and are processed by the Si1102’s analog circuitry. If the reflected light is above the detection
threshold, the Si1102 asserts the active-low PRX output to indicate proximity. This output can be used as a control
signal to activate other devices or as an interrupt signal for microcontrollers. Note that when the proximity of an
object nears the pre-set threshold, it is normal for the PRX pin to alternate between the on and off states. The
microcontroller can take the time average of PRX (assigning 1 as “no detect” and 0 as “detect”) and then compare
the average to 0.5 to achieve a sharper in-proximity or out-of-proximity decision.
To achieve maximum performance, high optical isolation is required between two light ports, one for the transmit
LED and the other for the Si1102. The Si1102 light port should be infrared-transmissive, blocking visible light
wavelengths for best performance. This dual-port active reflection proximity detector has significant advantages
over single-port, motion-based infrared systems, which are good only for triggered events. Motion detection only
identifies proximate moving objects and is ambiguous about stationary objects. The Si1102 allows in- or out-of-
proximity detection, reliably determining if an object has left the proximity field or is still in the field even when not
moving.
An example of a proximity detection application is controlling the display and speaker of a cellular telephone. In this
type of application, the cell phone turns off the power-consuming display and disables the loudspeaker when the
device is next to the ear, then reenables the display (and, optionally, the loudspeaker) when the phone moves more
than a few inches away from the ear.
For small objects, the drop in reflectance is as much as the fourth power of the distance; this means that there is
less range ambiguity than with passive motion-based devices. For example, a sixteen-fold change in an object's
reflectance means only a fifty-percent drop in detection range.
The Si1102 proximity detector is designed to operate with a minimal number of external components. Figure 1
shows a circuit example using a single 3.3 V power supply. The potentiometer, R1, is used to set the proximity
detection threshold. The Si1102 periodically detects proximity at a rate that can be programmed by a single resistor
(R2). The part is powered down between measurements. The resulting average current, including that of the LED,
can be as low as a few microamperes, which is well below a typical lithium battery's self-discharge current of
10 µA, thus ensuring the battery's typical life of 10 years.
When enabled (SREN driven low by a microcontroller or R1 pull-down potentiometer exists), the Si1102 powers
up, then pulses the output of the LED driver. Light reflected from a proximate object is detected by the receiver,
and, if it exceeds a threshold set by the potentiometer at the SREN pin, the proximity status is latched to the active-
low PRX output pin. The output is updated once per cycle. The cycle time is controlled through the optional R2
resistor.
Although the thresholds are normally set using a potentiometer for R1 (or R2), it is possible to digitally control
various resistance values by using MCU GPIO pins to switch-in different value resistors (or parallel combinations of
resistors). To activate the chosen resistor(s), the GPIO pin is held low, creating a pull-down resistor. For the
unwanted resistors, those specific MCU pins are kept tri-stated, rendering those resistors floating.
Figure 2. Timing Diagram
Rev. 1.0
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