Rev. 1.0 8/10 Copyright © 2010 by Silico n Laboratories Si1120
Si1120
PROXIMITY/AMBIENT LIGHT SENSOR WITH PWM OUTPUT
Features
Applications
Description
The Si1120 is a low-power, reflectance-based proximity and ambient light
sensor with advanced analog signal processing and analog PWM output.
It includes an integrated differential photodiode, signal processor, and
LED driver. Proximity sensing is based on the measurement of reflected
light from an external, optically-isolated, strobed LED. A separate visible
light photodiode is used for ambient light sensing. The standard package
for the Si1120 is an 8-pin ODFN.
Typically 50 cm meter prox im ity
range with single pulse
Seven precision optical
measurement modes:
3 proximity ranges
3 dc ambient ranges
1 calibration mod e
Low-noise ambient cancelling
circuit allows maximum
sensitivity with 8–12 bit resolution
ALS works in direct sunlight
(100 klux)
Minimum reflectance sensitivity
<1 µW/cm2
High EMI immunity without
shielded packaging
Power supply: 2.2–3.7 V
Operating temperature range:
–40 to +85 °C
Typical 10 µA current
consumption
Programmable 400/50 mA LED
constant curr ent driver output
Allows independent LED supply
voltage
Small outline 3 x 3 mm (ODFN)
Handsets
Touchless switches
Occupancy sensors
Consumer electronics
Notebooks/PCs
Industrial automation
Display backlighting control
Photo-interrupter
U.S. Patent #5,864,591
U.S. Patent #6,198,118
Other patents pending
Pin Assignments
MD
VSS
TXO
TXGD
SC
VDD
PRX
STX
1
2
3
4
8
7
6
5
Si1120
ODFN
Si1120
2 Rev. 1.0
Functional Block Diagram
Figure 1. Si1120 Typical Application Example of Digit al Proxim ity and Ambient Light Sensor with
C8051F931 MCU and I2C Interface
Infrared
emitter
Ambient Light
Sources
Product
Case
IR VIS
MUX AMP CMP
BUF PRX
VDD
TXO
TXGDVSS
MD
SC
STX
VREG
RAMP
GEN
MODE
CTRL TX
PWM
Output
Optical Block
Transparent
window Transparent
window
VDD / DC+
GND / DC-
DCEN
VBAT
GND
P0.0/VREF
P0.1 / AGND
P0.2 / XTAL1
P0.3 / XTAL2
P0.4 / TX
P0.5 / RX
P0.6 / CNVSTR
P0.7 / IREF0
P1.0
P1.1
P1.2
P1.3
P1.4
P1.5
P1.6
XTAL3
XTAL4
RST / C2CK
P2.7 / C2D
PRX
TXGD
TXO
STX
VSS
MD
SC
VDD
C8051F931
Si1120
C1
1.0 uF
C4
68.0 uF
R1
30 ohm C2
10 uF C3
0.1 uF
TX LED
3.3 V
Si1120
Rev. 1.0 3
TABLE OF CONTENTS
Section Page
1. Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
2. Application Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.1. Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
2.2. Mode Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
2.3. Proximity Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
2.4. Ambient-Light Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
2.5. Choice of LED and LED Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
2.6. Power-Supply Transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
2.7. Practical Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
3. Pin Descriptions—Si1120 (ODFN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
4. Ordering Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
5. Photodiode Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
6. Package Outline (8-Pin ODFN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Document Change List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Contact Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Si1120
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 Tem p er a tur e –40 — 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
*Note: S tresses above those listed in this table may cause permanent damage to the device. This is a stress rating only, and
functional operation of the devices at those or any other conditions above those indicated in the operational listings of
this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device
reliability.
Table 2. Recommended Operating Conditions
Parameter Symbol Conditions / Notes Min Typ Max Units
Typical Operating Conditions (TA=25°C)
Supply Voltage VDD T = –40 to +85 °C,
VDD to GND, TXGD 2.2 3.3 3.7 V
Operating Temperature –40 25 85 °C
SC/MD/STX High Threshold VIH VDD–0.7 — — V
SC/MD/STX Low Threshold VIL — — 0.6 V
Active TXO Voltage1——1.0V
ALS Operating Range Edc — — 100 kLx
Proximity Conversion Frequen cy2— 125 250 Hz
LED Emission Wavelength3600 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 TX O voltage.
2. When in Mode 0 and operating at 250 Hz, STX pulse width should be limited to 1 ms.
3. When using LEDs near the min and max wavelength limits, higher radiant intensities may be needed to achieve the end
system's proximity sensing performance goals.
Si1120
Rev. 1.0 5
Table 3. Electrical Characteristics
Parameter Symbol Conditions / Notes Min Typ Max Units
IDD Shutdown SC >VIH, VDD = 2. 7 to 3.7,
T=27°C —0.11.0µA
IDD Current Idle SC = STX <VIL — 90 150 µA
IDD Current During T ransmit,
Not Saturated VDD = 3.3 V, LED I = 400 mA — 14 — mA
IDD Current During T ransmit,
Not Saturated VDD =3.3V, LED I=50mA — 3 — mA
PRX Pulse Width Rang e Tprx VDD = 3.3 V 0.5 — 2500 us
PRX Logic High Level VOH IOH =–4mA V
DD–0.7 — — V
PRX Logic Low Level VOL IOL =4mA — — 0.6 V
Min. Detectable Reflectance Input Emin VDD = 3.3 V (Mode 0,2) — 1 — µW/cm2
Max. Detectable Reflectance Input Emax1 VDD = 2.2 V (Mode 3) — 12 — mW/cm2
Max. Detectable Reflectance Input Emax2 VDD = 3.7 V (Mode 3) — 48 — mW/cm2
Calibration Mode PRX Pulse Width Tpwcal VDD = 3.3 V, Mode 1 — 7 — us
TXO Leakage Current Itxo_sd VDD = 3.3 V, No strobe — 0.01 1 µA
TXO Current (TX High Power) Itxo VDD =3.3V,
TXO = 1 V (Mode 0) —400—mA
TXO Current (TX Low Power) Itxo VDD =3.3V,
TXO = 1 V (Mode 2,3) —50—mA
Power Up Latency* VDD =3.3V — — 535 µs
Full-Scale Ambient Light FSals1 VDD = 3.3 V, Mode 5 — 500 — Lx
Full-Scale Ambient Light FSals2 VDD = 3.3 V, Mode 6 — 100 — kLx
Full-Scale Ambient Light FSals3 VDD = 3.3 V, Mode 7 — 10 — kLx
*Note: Refer to "2.2. Mode Selection" on page 7 for additional information.
Si1120
6 Rev. 1.0
2. Application Information
2.1. Theory of Operation
The Si1120 is an active optical-reflectance proximity detector and ambient-light sensor with a pulse-width
modulated output. Depending on the mode selected, the duration of the PRX active (low) state is proportional to
the amount of reflected light, the amount of zero-ref lectance offset, or the amount of ambient light. The detection
rate can be set by adjusting the frequency of the STX signal.
The 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 Si1120 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 it is 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 mean s that there is
less range ambiguity than with passive motion-based devices. For example, a sixteen-fold change in an object's
reflectance me ans only a fif ty-percent drop in detection range. The Si1120 periodically measures proximity at a ra te
that can be set by an external controller.
The Si1120 modes are:
PRX400 Proximity, 400 mA LED current
PRX50 Proximity, 50 mA LED current
PRX50H Proximity, 50 mA LED current, high reflectance range
OFC Offset calibration (proximity mode, no LED current)
VAMB Visible ambient (10 klux sunlight)
VIRL Visible and infrared ambient light, low range (500 lux sunlight)
VIRH Visible and infrared ambient light, high range (128 klux sunlight)
Si1120
Rev. 1.0 7
2.2. Mode Selection
The Si1120 features a shutdown mode, three proximity-detection modes, three ambient-light sensing modes, and
an offset calibration for high-sensitivity mode. Mode selection is accomplished through the sequencing of the SC
(shutdown/clock), MD (mode), and STX (strobe/transmit) pins.
The part enters shutdown mode un co nd itio na lly wh e n SC is high. Each of the MD and STX inputs should be set to
a valid high or low state. In shutdown mode, the PRX output is tri-stated, and the power-supply and TXO output
leakage currents are negligible.
The active modes are set by clocking the state of MD and STX on the falling edge of SC and then setting MD to the
required state. Since setting SC high forces shutdown, SC must be held low for the selected mode to remain
active. The timing diagram in Figure 2 illustrates the programming sequence. Table 4 indicates the various mode
encodings. After the correct state has been programmed, the STX input is used to trigger measurements.
Figure 2. Si1120 Mode Programming Timing Diagram
If the mode must be changed, the SC pin may need to be rearmed (set high), in which case the shutdown mode is
set and a power-on latency of about 500 µs is incurred upon enabling of the selected mode when SC goes back
low. Following a mode change, STX must be kept low during the power-up latency period. If the host sets STX too
early, the Si1120 may not begin a measurement cycle; PRX does not assert. If this occurs, the host can restart a
measurement by toggling STX.
Table 4. Mode Control Table
Mode Description STX (Latch) MD (Latch) MD (Static)
PRX400 Proximity, 400 mA LED current (Mode 0) 0 0 0
OFC Offset calibration for high sensitivity (Mode 1) 0 0 1
PRX50 Proximity, 50 mA LED current (Mode 2) 0 1 0
PRX50H Proximity, 50 mA LED current, high reflectance (Mode 3) 0 1 1
VIRL Visible and infrared ambient, low range (Mode 4) 1 0 0
VAMB Visible ambient (Mode 5) 1 0 1
VIRH Visible and infrared ambient, high range (Mode 6) 1 1 0
(Reserved) Reserved mode 1 1 1
Si1120
8 Rev. 1.0
2.3. Proximity Modes
In proximity m ode, an LED send s light pulses th at 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 amoun t 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 th e detection cycle at a set time al so enables fast th reshold comp arison by samplin g the state o f 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 proximit y measurement
rate thus allowing more samples to be averaged for an overall increase in the signal-to-noise ratio.
For long-range dete ction, PRX400 mode is selected. For short-ra nge detection, PRX50 mo de 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 of fset calibratio n mode work s the same way as the othe r proximity modes b ut without turning o n the LED. This
allows precise measurement of the environment and Si1120 internal offsets without any LED light being reflected.
The of fset 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)
Si1120
Rev. 1.0 9
Figure 5. PRX400 Mode 0
Figure 6. PRX50 Mode 2
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000 1200 1400 1600 1800 2000
PRX Pulse Wi dth ( us)
Distance ( cm )
47%, H and, 1 Lux
47%, H and, 300 Lux Fl uorescent
47%, H and, 300 Lux In candescen t
18% G r ay Card, 1 Lux
92% White Card, 1 Lux
0
5
10
15
20
25
0 50 100 150 200 250 300
PRX Pulse Wi dt h (us)
Distance ( cm )
47%, Hand, 1 Lux
47%, Hand, 300 Lux Flu or es cent
47%, Hand, 300 Lux I ncan desc ent
18% G r ay Card, 1 Lux
92% White Card, 1 Lux
Si1120
10 Rev. 1.0
Figure 7. Combined PRX400 and PRX50
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000 1200 1400 1600 1800 2000
PRX Pul se W idth (us)
Distance (cm)
18% Gray Card, 4 00 mA
18% Gray Card, 5 0 m A
92% White , 400 m A
92% White , 50 m A
Si1120
Rev. 1.0 11
2.4. Ambient-Light Modes
Proximity offset and gain can be affected a few percent by high ambient light levels (e.g. sunlight or strong
incandescent lighting). While the cal mode can be used to determine offsets from large ambient light or ambient
noise levels in PRX400 and PRX50 modes, direct measurement of the ambient levels can help identify whether
changes in reflectance are valid or in fact due to large ambient light changes. Usually, this is only an is sue in high
reflectance situations, such as single window operation without good optical isolation, where large changing
ambients are an issue .
The Si1120 has two photodiodes, each of which peaks at a diffe rent wavelength. The VAMB mode uses the visible
light photodiode which peaks at arou nd 530 nm. On the other h and, th e VIRH a nd VIRL mod es use the photod iode
which peaks at around 830 nm. Although the visible-light photodiode peaks near 550 nm (considered the peak
wavelength of human perception), the Si1120 visible photodiode extends to infrared light as well. Similarly, the
Si1120 infrared photodiode detects infrared light as well as part of the visible light spectrum. The Si1120 treats
ultraviolet, visi ble , an d inf ra red ligh t as a cont inu ou s sp ect ru m .
The ratio between the visib le and infrar ed photodiode read ings provides a good clu e to the type of light source. The
reason is that each light source consists of a characteristic mix of infrared and visible light. For example, blackbody
radiators, such as incandescent or halogen lamps, can have significant energy in the infrared spectrum. On the
other hand, fluorescent lamps have more energy in the visible light spectrum. The term “color ratio” will be used to
describe the relative strength of the visible photodiode reading relative to the infrared photodiode reading. Human
color vision employs a similar principle.
The VAMB/VIRH or VAMB/VIRL color ratios are represent ative of the Si1120's color perception. Choosing between
these two color ratios depends on the light intensity. In general, VAMB/VIRL should be used first since VIRL has
higher sensitivity. For higher light intensities, the VAMB/VIRH ratio should be used.
Note that VAMB, VIRH, and VIRL pulse widths ar e used as dividend s and divisors in these ratios. What this means
is that the pulse width offsets (at 0 lux) need to be removed prior to usage in the above color ratios. For best
precision, it is best to take VAMB, VIRH, and VIRL measurements at 0 lux and to use actual measured values.
However, a good rule of thumb is to subtract 7.1 µs, 11.3 µs, and 9.9 µs respectively from VAMB, VIRH, and VIRL
(then assigning 0 µs to any resulting nega tive value). This ru le-of-thumb can b e used when accuracy is less critical.
Unless stated otherwise, the plots and figure s u se d in th is data sheet use offset-corrected values for VAMB, VIRH,
and VIRL.
Once a color ratio has been derived, the light type(s) and lux ratios are also identified. The lux ratio describes the
ratio between the desired lux value and VAMB, VIRL, or VIRH (depending on the situation). The appropriate lux
ratio, when multiplied with the applicable measurement, yields the final calculated lux value. Without any
calibration, it should be possible to arrive within 50% (or 50 lux) of the absolute lux value.
Figure 8. Ambient Light Mode Timing Diagram
Si1120
12 Rev. 1.0
Figure 9. Si1120 Typical Spectral Response
Figure 10. Sunlight Transfer Function
Figure 11. Low Light Transfer Function
Figure 12. Incandescent/Halogen Transfer
Function
Figure 13. CFL Transfer Function
Figure 14. Lux/VAMB vs. Color Ratio
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
400 500 600 700 800 900 1000
Wavelen gth (nm)
Normalized Response
VAMB VIRL
0
20
40
60
80
100
0 100 200 300 400 500 600 700
VIRH Pulse Width (VIRL, VAMB saturated)
Illuminance (KLUX)
0
20
40
60
80
100
120
140
0 200 400 600 800 1000 1200 1400
9,5/3XOVH:LGWK9,5/9$0%9,5/&RORU5DWLRa
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0
500
1000
1500
2000
2500
3000
3500
4000
0 400 800 1200 1600 2000
9$0%3XOVH:LGWK9$0%9,5+&RORU5DWLRa
,OOXPLQDQFH/8;
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300 350 400 450 500
9$0%3XOVH:LGWK9$0%9,5/&RORU5DWLR!
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0
0.5
1
1.5
2
2.5
3
3.5
4
10 15 20 25 30 35 40
9$0%9,5+&RORU5DWLR
/8;9$0%5DWLR
Si1120
Rev. 1.0 13
Figure 15. Lux/VIRL Ratio vs. Color Ratio
0
0.04
0.08
0.12
0.16
0.2
0.04 0.05 0.06 0.07 0.08 0.09 0.1
9$0%9,5/&RORU5DWLR
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Si1120
14 Rev. 1.0
2.5. 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.
Red LEDs do not permit the use of infrared filters and thus are more susceptible to am bient-lig ht noise. Th is ad ded
susceptibility effectively reduces the detection range. White LEDs have slow response and do not match the
Si1120’s spectral response well; they are, therefore, not recommended.
The Si1120 maintains excellent sensitivity in high ambient and optically noisy environments, most notably from
fluorescent lights. In very noisy environments, the maximum sensitivity may drop by a factor of up to one hundred,
causing a significant reduction in proximity range . With reduced sensitivity, the effect of optical environmental no ise
is reduced. For this reason, it is best to drive the LED with the maximum amount of current available, and an
efficient LED should be selected. With careful system design, the duty cycle can be made very low, thus enabling
most LEDs to handle the peak current of 400 mA while keeping the LED’s average current draw on the order of a
few microamperes. Total current consumption can be kept well below that of a typical lithium battery's self-
discharge current of 10 µA, thus ensuring the battery's typical life of 10 year s.
Another consideration when choosin g an LED is the LED's half-angle. An LED with a narrow ha lf-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.
2.6. Power-Supply Transients
2.6.1. VDD Supply
The Si1120 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 Si1120 itself produces sharp current transients, and, for this reason, must also have a bulk
capacitor on its supply pins. Current transients at the Si1120 supply can be up to 20 mA.
2.6.2. LED Supply
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 capa citor. If a regulated supply is available, the Si1120
should be connected to the regulator ’s output and the LED to the unregulated voltage, provided it is less than 6 V.
There is no power-sequencing requirement between VDD and the LED supply. The typical LED current peak of
400 mA can induce supp ly transients well over 50 mVpp, b ut those transients are easy to decouple with a simple
R-C filter because the duty-cycle-averaged LED current is quite low.
2.6.3. LED Supply (Single Port Configuration)
When using a single optical port, the Si1120 attempts to detect changes in reflection that can be less than one
percent of the received signal. A constant LED current is essential to avoid spurious detections. It is, therefore,
critical to prevent TXO saturation. If TXO is allowed to saturate in a single-port configuration, the Si1120 will be
very sensitive to LED power-supply variations and even to frequency variations at the STX input. A reservoir
capacitor should be chosen based on the expected TXO pulse width, and a series resistor should be selected
based on the STX duty cycle.
2.6.4. LED Supply (Dual Port Configuration)
When using separate optical ports for the LED and for the Si1120, the signal reflected from the target is large
compared with the internal reflection. This eliminates the need for keeping the LED current constant, and the TXO
output can, therefore, be allowed to saturate without problem. In addition, only the first 10 µs of the LED turn-on
time are critical to the detection range. This further reduces the need for large reservoir capacitors for the LED
supply. In most applications, a 10 µF capacitor is adequate. A 100 to 1 k resistor should be added in series to
minimize peak load current.
Si1120
Rev. 1.0 15
2.7. Practical Considerations
It is important to have an optical barrier between the LED and the Si1120. 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. A Dual-Port Optical Window shown in Figure 16 can accomplish this easily.
If an existing enclosure is being reused and does not have dedicated openings for the LED and the Si1120, the
proximity detector may still work if the optical loss factor through im provised 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) win dow (common in cellular telephones, PDAs, etc.) must be reduced
through careful component placement. To reduce the optical coupling from the LED to the Si1120 receiver, the
distance between the LED and the Si1120 should be maximized, and the dist an ce betwe en both components (LED
and Si1120) to the PMMA window should be minimized. The PRX50H mode can be used for the Single-Port
Optical Window shown in Figure 16.
Another practical consideration is that system optical leakage, overlay thickness and transmittance, LED efficiency
variation, TXO sink drive and photodiode part-to-part difference all collectively lead to reflectance measurement
variation even under a given proximity condition. For applications requiring PRX pulse width consistency across
multiple systems, factory calibration is recommended. Factory calibration involves t aking a r eference measurement
against a consistent and reproducible reflective object (such as an 18% gray card) at a fixed distance during
system production testing. Having this reference proximity measurement stored in non-volatile RAM or Flash
allows host software to make necessary adjustments to incoming PRX pulse widths against this reference
proximity measurement. A low background infrared environment is recommended.
For best proximity range performance, the system optical leakage c an be characterized during factory calibration.
To do this, a reference proximity measurement is made when it is known that no object is in proximity of the system
at the time of the me asureme nt. The 'no o bject' r efer ence me asur ement allo ws h ost software to establish the le ve l
of system optical leakage and make the necessary corrections to account for this.
In a similar way, for applications with heavy reliance on ALS accuracy, measurements using re ference light sources
during factory calibration can be used to make adjustments to VAMB, VIRL, and VIRH measurements.
Figure 16. Dual-Port and Single-Port Optical Window
PRX50
Mode
Transmit LED
Optical block
PRX400 Mode
Si1120
Internal Reflection
Transparent
window
Optical block
Transmit LED
Si1120
PRX50H Mode
Dual-port Optical Window Single-port Optical Window
Si1120
16 Rev. 1.0
3. Pin Descriptions—Si1120 (ODFN)
Figure 17. Pin Configurations
Table 5. Pin Descriptions
Pin Name Description
1PRXPWM Output.
Outputs a low-going PWM pulse proportional to signal.
2TXGDTXGD.
Power ground (LED and PRX driver ground return). Must be connected to VSS.
3TXOTransmit Output.
Normally connected to an infrar ed LED cathode. The output current is a program mable con-
stant current sink. This output can be allowed to saturate, and output current can be limited by
the addition of a res isto r in se rie s with th e LED.
4STXStrobe.
Initiates PS or ALS measurement. Also used as data input for the M2 internal mode control
flip-flop.
5V
DD Power Supply.
2.2 to 3.7 V voltage source.
6SCShutdown/Clock.
When high, shuts down the part. When enabling the p art, the low-going edge clocks the st ates
of STX and MD into mode-control D flip-flops M2 and M3.
7MDMode Control.
Controls two mode control bit s, one directly and the other indirectly, by providing the dat a input
for the M3 internal mode control flip-flop.
8 VSS VSS.
Ground (analog ground). Must be connected to TXGD.
MD
VSS
TXO
TXGD
SC
VDD
PRX
STX
1
2
3
4
8
7
6
5
Si1120
Rev. 1.0 17
4. Ordering Guide
5. Photodiode Centers
Part Ordering # Temperature Package
Si1120-A-GM –40 to +85 °C 3x3 mm ODFN8
Si1120
18 Rev. 1.0
6. Package Outline (8-Pin ODFN)
Figure 18 illustrates the package details for the Si1120 ODFN package. Table 6 lists the values for the dimensions
shown in the illustration.
Figure 18. 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 millimeters (mm).
2. Dimensioning and Tol erancing per ANSI Y14.5M-1994.
Si1120
Rev. 1.0 19
DOCUMENT CHANGE LIST
Revision 0.41 to Revision 0.42
Removed custom package option.
Updated Table 1 on page 4.
Added Operating, Storage temp s, and ESD to Table 1.
Updated "4. Ordering Guide" on page 17.
Added ordering part number information.
Added "6. Package Outline (8-Pin ODFN)" on page
18.
Updated " Functional Block Diagram" on page 2.
Added Figures 5, 6, and 7.
Updated "2.4. Ambient-Light Mo des" on page 11.
Added Figures 9, 10, 11,12, 13, 14, and 15.
Updated "2.5. Choice of LED and LED Current" on
page 14.
Revision 0.42 to Revision 0.43
Updated Table 3 on page 5.
Updated power up latency maximum value from 300 to
500 µs.
Updated FSals2 typical value from 128 to 100.
Updated "2.2. Mode Selection" on page 7.
Revision 0.43 to Revision 1.0
Updated Table 3 on page 5.
Widened limits of PRX Pulse Width Range
from 4 min / 2200 max to 0.5 min / 2500 max.
PRX Logic High Level changed to VDD – 0.7 from
VDD – 0.5.
Removed IDD current specification for saturated driver
condition.
Removed Tempe ra ture Coefficient specification.
Increased power-up latency from 500 to 535 µs.
Changed IDD Current Idle from 120 µA TYP to 90 µA
TYP and 300 µA Max to 150 µA Max.
Updated first paragrap h in "2. 4. Ambien t-L ig ht
Modes" on page 11.
Renamed Section “2.7. Mechan ical and Optical
Implementation” to “2.7. Practical Considerations” .
Added factory calibration guidance.
Added "5. Photodiode Centers" on page 17.
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