Si1102 Optical Proximity Detector

S i 1102
O PTICAL P ROXIMITY D ETECTOR
Features
Pin Assignments

High-performance proximity

detector with a sensing range of up
to 50 cm

 Single-pulse sensing mode for low 
system power
 Adjustable detection threshold and 
strobe frequency
 Proximity (PRX) status latch

enables controlling devices to
avoid missing a detection

High EMI immunity without
shielded packaging
2 to 5.25 V power supply
Operating temperature range:
–40 to +85 °C
Typical 10 µA current consumption
and ultra-low power of 1 mA typical
Current driven (400 mA) or
saturated LED driver output
Small outline: 3x3 mm (ODFN)
Si1102
ODFN
PRX
1
8
VSS
TXGD
2
7
FR
TXO
3
6
SREN
DNC
4
5
VDD
Applications

U.S. Patent 5,864,591

Proximity sensing
 Photo-interrupter
 Occupancy sensing
Touchless switch
 Object detection
 Handsets
 Intrusion/tamper detection
U.S. Patent 6,198,118
U.S. Patent 7,486,386
Other patents pending
Description
The Si1102 is a high-performance (0–50 cm) active proximity detector.
Because it operates on an absolute reflectance threshold principle, it avoids
the ambiguity of motion-based proximity systems.
The Si1102 consists of a patented, high-EMI immunity, differential photodiode
and a signal-processing IC with LED driver and high-gain optical receiver.
Proximity detection is based on measurements of reflected light from a
strobed, optically-isolated LED. The standard package for the Si1102 is an 8pin ODFN.
Functional Block Diagram
Reflectance-Based Proximity Detection
PRX
Signal
processing
Infrared
emitter
Product
Case
Hi-Lo
Threshold
Output
SREN
IR
FR
Oscillator
VDD
Shutdown
control
LED
Drive
TXO
VSS
Rev. 1.0 11/10
Copyright © 2010 by Silicon Laboratories
Si1102
Si11 02
2
Rev. 1.0
Si1102
TABLE O F C ONTENTS
Section
Page
1. Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
2. Typical Application Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
3. Application Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.1. Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
3.2. Choice of LED and LED Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
3.3. Power-Supply Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
3.4. Mechanical and Optical Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
3.5. Typical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Pin Descriptions—Si1102 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Ordering Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Photodiode Center . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Package Outline (8-Pin ODFN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Document Change List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Contact Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Rev. 1.0
3
Si11 02
1. Electrical Specifications
Table 1. Absolute Maximum Ratings
Conditions
Min
Typ
Max
Units
Supply Voltage
–0.3
—
5.5
V
Operating Temperature
–55
—
85
°C
Storage Temperature
–65
—
85
°C
Voltage on TXO with respect to
GND
–0.3
—
5.5
V
Voltage on all other Pins with
respect to GND
–0.3
—
VDD + 0.3
V
Maximum total current through
TXO (TXO Active)
—
—
500
mA
Maximum Total Current through
TXGD and VSS
—
—
600
mA
Maximum Total Current through
all other Pins
—
—
100
mA
—
—
2
kV
Parameter
ESD Rating
Human body model
Table 2. Recommended Operating Conditions
Parameter
Supply Voltage
Symbol
Conditions/Notes
Min
Typ
Max
Units
VDD
–40 to +85 °C, VDD to VSS
2.2
3.3
5.25
V
–40
25
85
°C
Operating Temperature
SREN High Threshold
VIH
VDD – 0.6
—
—
V
SREN Low Threshold
VIL
—
—
0.6
V
—
—
1.0
V
VDD = 3.3 V, 1 kHz–10 MHz no
spurious PRX or less than 20%
reduction in range
—
—
50
mVPP
on VDD
VDD = 3.3 V
—
1
100
klux
600
850
950
nm
Active TXO Voltage1
Peak-to-Peak Power Supply
Noise Rejection
DC Ambient light
Edc
LED Emission Wavelength2
Notes:
1. Minimum R1 resistance should be calculated based on LED forward voltage, maximum LED current, LED voltage rail
used, and maximum active TXO voltage.
2. When using LEDs near the min and max wavelength limits, higher radiant intensities may be needed to achieve the
system's proximity sensing performance goals.
4
Rev. 1.0
Si1102
Table 3. Electrical Characteristics
Symbol
Conditions/Notes
Min
Typ
Max
Units
PRX Logic High Level
VOH
VDD = 3.3 V, Iprx = 4 mA
VDD – 0.6
—
—
V
PRX Logic Low Level
VOL
VDD = 3.3 V, Iprx = –4 mA
—
—
0.6
V
IDD Shutdown
IDD
SREN = VDD, FR = 0,
VDD = 3.3 V
—
0.1
1.0
µA
IDD Average Current
SREN = 0 V, VDD = 3.3 V, FR = 0
30
120
200
µA
IDD Average Current
SREN = 0 V, VDD = 3.3 V,
FR = open
—
5
20
µA
IDD Current during Transmit,
Saturated Driver
VDD = 3.3 V, LED I = 100 mA
—
8
—
mA
IDD Current during Transmit,
Not Saturated
VDD = 3.3 V, LED I = 400 mA
5
14
30
mA
Parameter
Sample Strobe Rate1
FR
VDD = 3.3 V, R2 = 0 
100
250
600
Hz
Sample Strobe Rate1
FR
VDD = 3.3 V, R2 = 100 k
—
7
30
Hz
Sample Strobe Rate1
FR
VDD = 3.3 V, R2 = (open)
—
2
8
Hz
Min. Detectable
Reflectance Input
Emin
VDD = 3.3 V, 850 nm source
—
1
—
µW/
cm2
SREN Low to TXO Active
Tden
VDD = 3.3 V
200
500
1000
µs
Itxo_sd
VDD = 3.3 V, no strobe
—
0.01
1
µA
TXO Current2
Itxo1V
VTXO = 1 V, VDD = 3.3 V
100
380
600
mA
TXO Saturation Voltage
Vsat
ITXO = ITXO1V x 80%
—
0.5
0.7
V
TXO Leakage Current
Notes:
1. Max column also applies to VDD > 3.6 V. See Figure 6.
2. When operating at VDD = 2.0 V, the typical TXO current is 250 mA.
Rev. 1.0
5
Si11 02
2. Typical Application Schematic
VDD
R3
5
C1
0.1 µF
C2
1
PRX
10 µF
2
3
C3
TxLED
4
PRX
VSS
TXGD
FR
TXO
SREN
DNC
VDD
Si1102
10 µF
8
7
6
5
R1
100 k
R2
100 k
VSS
Note: R1 resistance should be factory-adjustable to achieve a consistent proximity object detection threshold across
different combinations of irLED, product window, and sensor sensitivity.
Figure 1. Application Example of the Proximity Sensor Using a Single Supply
6
Rev. 1.0
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-ofproximity 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 activelow 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
7
Si11 02
3.2. Choice of LED and LED Current
In order to maximize detection distance, the use of an infrared LED is recommended. However, red (visible) LEDs
are viable in applications where a visible flashing LED may be useful and a shorter detection range is acceptable.
White LEDs have slow response and do not match the Si1102’s spectral response well; they are, therefore, not
recommended.
To maximize proximity detection distance, an LED with a peak current handling of 400 mA is recommended. With
careful system design, the duty cycle can be made low, enabling most LEDs to handle this peak current while
keeping the LED's average current draw on the order of a few microamperes.
Another consideration when choosing an LED is the LED's half-angle. An LED with a narrow half-angle focuses the
available infrared light using a narrower beam. When the concentrated infrared light encounters an object, the
reflection is much brighter. Detection of human-size objects one meter away can be achieved when choosing an
LED with a narrower half-angle and coupling it with an infrared filter on the enclosure.
3.3. Power-Supply Transients
Despite the Si1102's extreme sensitivity, it has good immunity from power-supply ripple, which should be kept
below 50 mVpp for optimum performance. Power-supply transients (at the given amplitude, frequency, and phase)
can cause either spurious detections or a reduction in sensitivity if they occur at any time within the 300 µs prior to
the LED being turned on. Supply transients occurring after the LED has been turned off have no effect since the
proximity state is latched until the next cycle. The Si1102 itself produces sharp current transients on its VDD pin,
and, for this reason, must also have a low-impedance capacitor on its supply pins. Current transients at the Si1102
supply can be up to 20 mA.
The typical LED current peak of 400 mA can induce supply transients well over 50 mVpp, but those transients are
easy to decouple with a simple R-C filter because the duty-cycle-averaged LED current is quite low. The TXO
output can be allowed to saturate without problem. Only the first 10 µs of the LED turn-on time are critical to the
detection range; this further lessens the need for large reservoir capacitors on the LED supply. In most
applications, 10 µF is adequate. If the LED is powered directly from a battery or limited-current source, it is
desirable to minimize the load peak current by adding a resistor in series with the LED’s supply capacitor.
If a regulated supply is available, the Si1102 should be connected to the regulator’s output and the LED to the
unregulated voltage, provided it is less than 7 V. There is no power-sequencing requirement between VDD and the
LED supply.
3.4. Mechanical and Optical Implementation
It is important to have an optical barrier between the LED and the Si1102. The reflection from objects to be
detected can be very weak since, for small objects within the LED's emission angle, the amplitude of the reflected
signal decreases in proportion with the fourth power of the distance. The receiver can detect a signal with an
irradiance of 1 µW/cm2. An efficient LED typically can drive to a radiant intensity of 100 mW/sr. Hypothetically, if
this LED were to couple its light directly into the receiver, the receiver would be unable to detect any 1 µW/cm2
signal since the 100 mW/cm2 leakage would saturate the receiver. Therefore, to detect the 1 µW/cm2 signal, the
internal optical coupling (e.g. internal reflection) from the LED to the receiver must be minimized to the same order
of magnitude (decrease by 105) as the signal the receiver is attempting to detect. As it is also possible for some
LEDs to drive a radiant intensity of 400 mW/sr, it is good practice to optically decouple the LED from the source by
a factor of 106.
If an existing enclosure is being reused and does not have dedicated openings for the LED and the Si1102, the
proximity detector may still work if the optical loss factor through improvised windows (e.g. nearby microphone or
fan holes) or semi-opaque material is not more than 90% in each direction. In addition, the internal reflection from
an encased device's PMMA (acrylic glass) window (common in cellular telephones, PDAs, etc.) must be reduced
through careful component placement. To reduce the optical coupling from the LED to the Si1102 receiver, the
distance between the LED and the Si1102 should be maximized, and the distance between both components (LED
and Si1102) to the PMMA window should be minimized. The detector can also work without a dedicated window if
a semi-opaque plastic case is used.
8
Rev. 1.0
Si1102
For applications where R1 resistance values are small, the proximity range can vary as a function of the ambient IR
condition. A product cover, which limits the visible light intensity, is helpful in reducing this range variation. It is
recommended that the Si1102 be evaluated and tested in-product under the various light conditions it will
encounter under normal product usage. Setting the potentiometer R1 = 0 is not recommended unless the ambient
light condition is known and relatively constant.
At any given R1 threshold setting, there are many factors that determine the precise distance that the Si1102
reports. These factors include object reflectivity, object size, ambient light type and ambient light intensity. When
used in applications where the ambient light is variable, it is recommended the Si1102 optical window be IR
transmissive but visible light opaque.
Table 4. Summary of External Component Values and Operating Conditions
R1
R2
Strobe Frequency
Distance1
IDD Average Current Consumption2
50 k
0
250 Hz
12 to 22 cm
100 µA
50 k
Open
2.0 Hz
12 to 22 cm
5 µA
15 k
0
250 Hz
40 to 50 cm
100 µA
30 k
0
250 Hz
17 to 33 cm
100 µA
Notes:
1. Distance measured with SFH4650 IR LED, with an IR filter, targeting an 18% gray card, 300 lux (Incandescent or CFL)
2. Average current consumption at VDD = 3.3 V, 25 °C and dark ambient conditions (<100 lx).
Detection Distance (cm)
Detection Distance
50
45
40
35
30
25
20
15
10
5
10
20
30
40
50
60
70
80
90
100
R1(kohm)
Figure 3. Proximity Detection Distance vs. R1 (SFH4650 IR LED 850 nm/40 mW)*
*Note: Detection range measured using Kodak Gray cards (18% reflectance), no IR filter under dark ambient conditions (<1 lx).
Rev. 1.0
9
Si11 02
3.5. Typical Characteristics
Cycle Period vs R1
Supply Current Idle
1000
1000
100
100
5.0 volts
2.0 volts
3.3 volts
10
3.3 volts
Current (uA)
Cycle Period (ms)
5.0 volts
10
2.0 volts
1
1
0
20
40
60
80
100
0
20
R1 (Kohm)
60
80
100
R2 (Kohm)
Figure 4. Cycle Period vs. R2
(R1 = 5.1 k, Vtxo = 1 V)
Figure 7. Idle Supply Current vs. R2
(R1 = 5.1 k, Vtxo = 1 V)
Idd Idle
Idd Idle vs VDD
95
180
160
5.0 volts
90
3.3 volts
2.0 volts
85
140
80
Idd ( uA)
Idd Idle
40
120
100
75
70
65
60
80
55
60
0
20
40
60
80
50
100
2
R1 (Kohm)
Cycle Time vs VDD
150
140
130
120
Cycle Time (ms)
110
100
R2=100K
90
R2=75K
80
R2=50K
70
R2=30K
60
R2=20K
50
40
R2=10K
30
R2=4.7K
20
10
0
3
3.5
4
4.5
VDD (V)
Figure 6. Cycle Period vs. VDD
(R1 = 5.1 k, Vtxo = 1 V)
10
3.5
4
4.5
Figure 8. Idle Supply Current vs VDD
(R1 = 5.1 k, R2 = 0 , Vtxo = 1 V)
160
2.5
3
VDD (V)
Figure 5. Idle Supply Current vs. R1
(R2 = 0 k, Vtxo = 1 V)
2
2.5
Rev. 1.0
Si1102
Detection Distance
Detection Distance (cm)
40
35
18% Gray Card, CFL 300 lx
30
82% White Card CFL 300 lx
25
18% Gray Card, Incandescent
300 lx
82% White Card, Incandescent
300 lx
20
15
10
5
10
20
30
40
50
60
70
80
90
100
R1 (kohm)
Figure 9. Proximity Detection Distance vs. Target Reflectivity (with IR Filter)
Detection Distance
Detection Distance (cm)
40
35
30
18% Gray Card, 0 lx
18% Gray Card, CFL 300 lx
18% Gray Card, CFL 1000 lx
25
20
15
10
5
20
30
40
50
60
70
80
90
100
R1 (kohm)
Figure 10. Proximity Detection Distance vs. Ambient Light (with IR Filter)
Rev. 1.0
11
Si11 02
4. Pin Descriptions—Si1102
PRX
1
8
VSS
TXGD
2
7
FR
TXO
3
6
SREN
NC
4
5
VDD
Figure 11. Pin Configuration
Table 5. Pin Descriptions
12
Pin
Name
Type
Description
1
PRX
Output
Proximity Output.
Normally high; goes low when proximity is detected. When device is not
enabled, the PRX pulls-up to VDD.
2
TXGD
Ground
TXGD.
Transmit ground (includes PRX return and other digital signals).
Must be connected to VSS.
3
TXO
Output
Transmit Output Strobe.
Normally connected to an infrared LED cathode. This output can be allowed
to saturate, and output current can be limited by the addition of a resistor in
series with the LED. It can also be connected to an independent unregulated
LED supply even if the VDD supply is at 0 V without either drawing current or
causing latchup problems.
4
NC
5
VDD
Input
Power Supply.
2 to 5.25 V voltage source
6
SREN
Input
Sensitivity Resistor/ENable.
Driving SREN below 1 V or connecting resistance from SREN to VSS
enables the chip and immediately starts a proximity measurement cycle. A
potentiometer to VSS controls proximity sensitivity. R1 = 0 yields maximum
detection distance. If SREN is high and FR is low (SREN = VDD, FR = 0), part
is in shutdown.
7
FR
Input
Frequency Resistor.
A resistor to VSS controls the proximity-detection cycle frequency. With no
resistor, the sample frequency is, at most, 5.0 Hz. With FR shorted to VSS
the sample frequency is typically 250 Hz. With a 100 k resistor, the sample
frequency is typically 7 Hz, maximum 30 Hz. The voltage on FR relative to
ground is only about 30 mV.
8
VSS
Ground
Do not connect.
VSS.
Ground (analog ground).
Rev. 1.0
Si1102
5. Ordering Guide
Part Ordering #
Temperature
Package
Si1102-A-GM
–40 to +85 °C
3x3 mm ODFN8
6. Photodiode Center
1.5
0.8
Figure 12. Photodiode Center
Rev. 1.0
13
Si11 02
7. Package Outline (8-Pin ODFN)
Figure 13 illustrates the package details for the Si1102 ODFN package. Table 6 lists the values for the dimensions
shown in the illustration.
Figure 13. ODFN Package Diagram Dimensions
Table 6. Package Diagram Dimensions
Dimension
Min
Nom
Max
A
0.55
0.65
0.75
b
0.25
0.30
0.35
D
D2
3.00 BSC.
1.40
1.50
e
0.65 BSC.
E
3.00 BSC.
1.60
E2
2.20
2.30
2.40
L
0.30
0.35
0.40
aaa
0.10
bbb
0.10
ccc
0.08
ddd
0.10
Notes:
1. All dimensions shown are in millimeters (mm).
2. Dimensioning and Tolerancing per ANSI Y14.5M-1994.
14
Rev. 1.0
Si1102
DOCUMENT CHANGE LIST
Revision 0.6 to Revision 0.7

Revised outline drawing for 3x3 ODFN.
Adjusted
pin width to match true scale
tolerance on body dimensions
Tightened
Revision 0.7 to Revision 0.8


Updated Tables 1, 2, 3, 4, and 5.
Updated Figures 1, 2, 3, 5, 11, and 12.
Revision 0.8 to Revision 1.0




Updated Table 2, Table 3, and Table 5
Updated Figure 1 and Figure 6.
Updated Section 3.4 concerning usage of small R1
values.
Added "6. Photodiode Center" on page 13.
Rev. 1.0
15
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Trademark Information
Silicon Laboratories Inc.® , Silicon Laboratories®, Silicon Labs®, SiLabs® and the Silicon Labs logo®, Bluegiga®, Bluegiga Logo®, Clockbuilder®, CMEMS®, DSPLL®, EFM®, EFM32®,
EFR, Ember®, Energy Micro, Energy Micro logo and combinations thereof, "the world’s most energy friendly microcontrollers", Ember®, EZLink®, EZRadio®, EZRadioPRO®, Gecko®,
ISOmodem®, Precision32®, ProSLIC®, Simplicity Studio®, SiPHY®, Telegesis, the Telegesis Logo®, USBXpress® and others are trademarks or registered trademarks of Silicon Laboratories Inc. ARM, CORTEX, Cortex-M3 and THUMB are trademarks or registered trademarks of ARM Holdings. Keil is a registered trademark of ARM Limited. All other products or brand
names mentioned herein are trademarks of their respective holders.
Silicon Laboratories Inc.
400 West Cesar Chavez
Austin, TX 78701
USA
http://www.silabs.com