SI1102-A-GMR - SILICON LABS

Si1102

OPTICAL PROXIMITY DETECTOR

Features

Applications

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, dif feren tial 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 8-

pin ODFN.

Functional Block Diagram

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)

Proximity sensing

Photo-interrupter

Occupancy sensing

Touchless switch

Object detection

Handsets

Intrusion/tamper detection

Signal

processing

PRX

SREN

TXO

VSS

LED

Drive

Shutdown

control

Oscillator

VDD

Infrared

emitter

Product

Case

Hi-Lo

Threshold

Output

Reflectance-Based Proximity Detection

U.S. Patent 5,864,591

U.S. Patent 6,198,118

U.S. Patent 7,486,386

Other patents pend ing

Pin Assignments

VSS

TXO

TXGD

SREN

VDD

PRX

DNC

Si1102

ODFN

Si1102

2 Rev. 1.0

Si1102

Rev. 1.0 3

TABLE OF CONTENTS

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

Si1102

4 Rev. 1.0

1. Electrical Specifications

Table 1. Absolute Maximum Ratings

Parameter 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) ——500mA

Maximum Total Current through

TXGD and VSS ——600mA

Maximum Total Current through

all other Pins ——100mA

ESD Rating Human body model — — 2 kV

Table 2. Recommended Operating Conditions

Parameter Symbol Conditions/Notes Min Typ Max Units

Supply Voltage VDD –40 to +85 °C, VDD to VSS 2.2 3.3 5.25 V

Operating Temperature –40 25 85 °C

SREN High Threshold VIH VDD – 0.6 — — V

SREN Low Threshold VIL — — 0.6 V

Active TXO Voltage1——1.0V

Peak-to-Peak Power Supply

Noise Rejection VDD =3.3V, 1kHz–10MHz no

spurious PRX or less than 20%

reduction in range

— — 50 mVPP

on VDD

DC Ambient light Edc VDD =3.3V — 1 100 klux

LED Emission Wavelength2600 850 950 nm

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.

Si1102

Rev. 1.0 5

Table 3. Electrical Characteristics

Parameter Symbol Conditions/Notes Min Typ Max Units

PRX Logic High Level VOH VDD =3.3V, Iprx=4mA 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 =3.3V —0.11.0µA

IDD Average Current SREN = 0 V, VDD = 3.3 V, FR = 0 30 120 200 µA

IDD Average Current SREN = 0 V, VDD =3.3V,

FR = open —520µA

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

Sample Strobe Rate1FR VDD = 3.3 V, R2 = 0 100 250 600 Hz

Sample Strobe Rate1FR VDD =3.3V, R2=100k—730Hz

Sample Strobe Rate1FR 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

TXO Leakage Current Itxo_sd VDD = 3.3 V, no strobe — 0.01 1 µA

TXO Current2Itxo1V VTXO =1V, V

DD = 3.3 V 100 380 600 mA

TXO Saturation Voltage Vsat ITXO = ITXO1V x 80% — 0.5 0.7 V

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.

Si1102

6 Rev. 1.0

2. Typical Application Schematic

Figure 1. Application Example of the Proximity Sensor Using a Single Supply

PRX PRX

TXGD

3TXO

4DNC

VSS

SREN

VDD

Si1102

VDD

VSS

C1 C2

TxLED R1 R2

0.1 µF 10 µF

10 µF

5 

100 k100 k

Note: R1 resistance should be factory-adjustable to achieve a consiste nt proximity obj e ct dete ction threshold across

different combinations of irLED, produc t window, and sensor sensitivity.

Si1102

Rev. 1.0 7

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 ac tive -lo w PRX output to ind i cat e p ro xim ity. Th is o ut pu t ca n be used as a contr ol

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 reenab les the display (and, option ally, the loudspeaker ) when the phone mo ves 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 me ans that there is

less range ambiguity than with passive motion-based devices. For example, a sixteen-fold change in an object's

reflectance means on ly a fifty-pe r cen t dr op in det ec tio n ra nge.

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 detect s 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 va lue resistors (or pa rallel 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 resisto rs floa tin g.

Figure 2. Timing Diagram

Si1102

8 Rev. 1.0

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 dra w 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 th e next cycle. The Si1102 itself produces sharp c urrent transients on its VDD pin,

and, for this reason , mu st also have a low-i mpe dan ce capacitor on its supp ly pin s. Curr ent tran sients 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 th e load peak current by adding a resistor in serie s 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 volt age, 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 th e 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 dev ice'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

dista nce between the LED and the Si1102 should be maximize d, and the distance betwe en both comp onent s (LED

and Si1102) to the PMMA window should be minimized. The detect or ca n also wor k wit hout a ded icated wi ndow if

a semi-opaque plastic case is used .

Si1102

Rev. 1.0 9

For applications where R1 resist ance values are small, th e proximity range can vary as a fu nction 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.

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).

Table 4. Summary of External Component Values and Operating Conditions

R1 R2 Strobe Frequency Distance1IDD 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 cond itions (<100 lx).

Detecti o n Distance

10 20 30 40 50 60 70 80 90 100

R1(kohm)

Detecti on Distance (cm )

Si1102

10 Rev. 1.0

3.5. Typical Characteristics

Figure 4. Cycle Period vs. R2

(R1 = 5.1 k, Vtxo = 1 V)

Figure 5. Idle Supply Current vs. R1

(R2 = 0 k, Vtxo = 1 V)

Figure 6. Cycle Period vs. VDD

(R1 = 5.1 k, Vtxo = 1 V)

Figure 7. Idle Supply Current vs. R2

(R1=5.1k, Vtxo = 1 V)

Figure 8. Idle Supply Current vs VDD

(R1=5.1k, R2 = 0 , Vtxo = 1 V)

Cycle Period vs R1

100

1000

0 20406080100

R1 (Kohm)

Cycle Period (ms)

5.0 volts

3.3 volts

2.0 volts

Idd Idle

100

120

140

160

180

0 20406080100

R1 (Kohm )

Idd Idle

5.0 vol t s

3.3 vol t s

2.0 vol t s

100

110

120

130

140

150

160

2 2.5 3 3.5 4 4.5

Cycle Time (ms)

VDD (V)

Cycle Time vs VDD

R2=100K

R2=75K

R2=50K

R2=30K

R2=20K

R2=10K

R2=4.7K

Supply Cur r ent Idl e

100

1000

0 20406080100

R2 ( Kohm)

Current (uA)

5.0 volts

3.3 volts

2.0 volts

Idd Idle vs VDD

22.533.544.5

VDD (V)

Idd ( uA)

Si1102

Rev. 1.0 11

Figure 9. Proximity Detection Distance vs. Target Reflectivity (with IR Filter)

Figure 10. Proximity Detection Distance vs. Ambient Light (with IR Filter)

Det ection Di stance

10 20 30 40 50 60 70 80 90 100

R1 (kohm)

Det ection Distance (cm)

18% Gray Card, CFL 300 l x

82% White Card CFL 300 lx

18% Gray Ca rd, Incandescent

300 lx

82% Wh ite Card, Incandescent

300 lx

Det ection Distance

20 30 40 50 60 70 80 90 100

R1 ( kohm )

Detect ion Distance (cm)

18% Gray Car d, 0 lx

18% Gray Car d, CFL 300 lx

18% Gray Car d, CFL 1000 lx

Si1102

12 Rev. 1.0

4. Pin Descriptions—Si1102

Figure 11. Pin Configuration

Table 5. Pin Descriptions

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.

2TXGDGround

TXGD.

Transmit grou nd (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 conn ecte d to a n inde pen de nt un re gulated

LED supply even if the VDD supply is at 0 V without either drawing current or

causing latchup problems.

4 NC Do not connect.

5VDD 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 dist ance. 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 VSS.

Ground (analog ground).

PRX

TXGD

TXO

VSS

SREN

VDD

Si1102

Rev. 1.0 13

5. Ordering Guide

6. Photodiode Center

Figure 12. Photodiode Center

Part Ordering # Temperature Package

Si1102-A-GM –40 to +85 °C 3x3 mm ODFN8

1.5

0.8

Si1102

14 Rev. 1.0

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 3.00 BSC.

D2 1.40 1.50 1.60

e 0.65 BSC.

E 3.00 BSC.

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 millime ters (mm).

2. Dimensioning and Tolerancing per ANSI Y14.5M-1994.

Si1102

Rev. 1.0 15

DOCUMENT CHANGE LIST

Revision 0.6 to Revision 0.7

Revised outline drawing for 3x3 ODFN.

Adjusted pin width to match true scale

Tightened tolerance on body dimensions

Revision 0.7 to Revision 0.8

Updated Tables 1, 2, 3, 4, an d 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 con cern in g usa ge of sma ll R1

values.

Added "6. Photodiode Center" on page 13.

Si1102

16 Rev. 1.0

CONTACT INFORMATION

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Austin, TX 78701

Tel: 1+(512) 416-8500

Fax: 1+(512) 416-9669

Toll Free: 1+(877) 444-3032

Please visit the Silicon Labs Technical Support web page:

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and register to submit a technical support request.

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