Si1120 Proximity/Ambient Light Sensor with PWM Output

S i 1120
P ROXIMITY / A MBIENT L IGHT S ENSOR W I T H PWM O UTPUT
Features
Pin Assignments
Typically 50 cm meter proximity  High EMI immunity without
range with single pulse
shielded packaging
 Seven precision optical
 Power supply: 2.2–3.7 V
measurement modes:
 Operating temperature range:
3 proximity ranges
–40 to +85 °C
3 dc ambient ranges
 Typical 10 µA current
1 calibration mode
consumption
 Low-noise ambient cancelling
 Programmable 400/50 mA LED
circuit allows maximum
constant current driver output
sensitivity with 8–12 bit resolution
 Allows independent LED supply
 ALS works in direct sunlight
voltage
(100 klux)
 Small outline 3 x 3 mm (ODFN)
 Minimum reflectance sensitivity
<1 µW/cm2

Si1120
ODFN
PRX
1
8
VSS
TXGD
2
7
MD
TXO
3
6
SC
STX
4
5
VDD
U.S. Patent #5,864,591
U.S. Patent #6,198,118
Other patents pending
Applications

Handsets
 Touchless switches
 Occupancy sensors
 Consumer electronics

Notebooks/PCs
 Industrial automation
 Display backlighting control
 Photo-interrupter
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.
Rev. 1.0 8/10
Copyright © 2010 by Silicon Laboratories
Si1120
Si11 20
Functional Block Diagram
Ambient Light
Sources
Transparent
window
Transparent
window
MUX
AMP
CMP
Infrared
emitter
PRX
BUF
PWM
Output
IR
VIS
Product
Case
RAMP
GEN
VDD
VREG
STX
Optical Block
SC
TXO
MODE
CTRL
TX
MD
VSS
TXGD
3.3 V
P0.0/VREF
VDD / DC+
C1
1.0 uF
GND / DC-
C8051F931
DCEN
VBAT
GND
Si1120
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
PRX
VSS
TXGD
MD
TXO
SC
STX
VDD
TX LED
XTAL3
XTAL4
C4
68.0 uF
R1
30 ohm
C2
10 uF
C3
0.1 uF
RST / C2CK
P2.7 / C2D
Figure 1. Si1120 Typical Application Example of Digital Proximity and Ambient Light Sensor with
C8051F931 MCU and I2C Interface
2
Rev. 1.0
Si1120
TABLE O F C ONTENTS
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
Rev. 1.0
3
Si11 20
1. Electrical Specifications
Table 1. Absolute Maximum Ratings*
Parameter
Conditions
Min
Typ
Max
Units
Supply Voltage
–0.3
—
5.5
V
Operating Temperature
–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)
—
—
500
mA
Maximum Total Current through
TXGD and VSS
—
—
600
mA
Maximum Total Current through
all other Pins
—
—
100
mA
—
—
2
kV
ESD Rating
Human body model
*Note: Stresses 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
T = –40 to +85 °C,
VDD to GND, TXGD
2.2
3.3
3.7
V
–40
25
85
°C
Typical Operating Conditions (TA = 25 °C)
Supply Voltage
VDD
Operating Temperature
SC/MD/STX High Threshold
VIH
VDD–0.7
—
—
V
SC/MD/STX Low Threshold
VIL
—
—
0.6
V
—
—
1.0
V
—
—
100
kLx
—
125
250
Hz
600
850
950
nm
Active TXO Voltage
1
ALS Operating Range
Edc
Proximity Conversion Frequency2
LED Emission Wavelength3
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 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.
4
Rev. 1.0
Si1120
Table 3. Electrical Characteristics
Parameter
Symbol
Conditions / Notes
Min
Typ
Max
Units
SC >VIH, VDD = 2.7 to 3.7,
T = 27 °C
—
0.1
1.0
µA
SC = STX <VIL
—
90
150
µA
IDD Current During Transmit,
Not Saturated
VDD = 3.3 V, LED I = 400 mA
—
14
—
mA
IDD Current During Transmit,
Not Saturated
VDD = 3.3 V, LED I = 50 mA
—
3
—
mA
IDD Shutdown
IDD Current Idle
PRX Pulse Width Range
Tprx
VDD = 3.3 V
0.5
—
2500
us
PRX Logic High Level
VOH
IOH = –4 mA
VDD–0.7
—
—
V
PRX Logic Low Level
VOL
IOL = 4 mA
—
—
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
Itxo_sd
VDD = 3.3 V, No strobe
—
0.01
1
µA
TXO Current (TX High Power)
Itxo
VDD = 3.3 V,
TXO = 1 V (Mode 0)
—
400
—
mA
TXO Current (TX Low Power)
Itxo
VDD = 3.3 V,
TXO = 1 V (Mode 2,3)
—
50
—
mA
VDD = 3.3 V
—
—
535
µs
TXO Leakage Current
Power Up Latency*
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.
Rev. 1.0
5
Si11 20
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-reflectance 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 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 Si1120 periodically measures proximity at a rate
that can be set by an external controller.
The Si1120 modes are:







6
PRX400
PRX50
PRX50H
OFC
VAMB
VIRL
VIRH
Proximity, 400 mA LED current
Proximity, 50 mA LED current
Proximity, 50 mA LED current, high reflectance range
Offset calibration (proximity mode, no LED current)
Visible ambient (10 klux sunlight)
Visible and infrared ambient light, low range (500 lux sunlight)
Visible and infrared ambient light, high range (128 klux sunlight)
Rev. 1.0
Si1120
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 unconditionally when 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
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
1
1
1
(Reserved) Reserved mode
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.
Rev. 1.0
7
Si11 20
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)
8
Rev. 1.0
Si1120
40
35
47%, Hand, 1 Lux
30
47%, Hand, 300 Lux Fluorescent
47%, Hand, 300 Lux Incandescent
Distance (cm)
25
18% Gray Card, 1 Lux
92% White Card, 1 Lux
20
15
10
5
0
0
200
400
600
800
1000
1200
1400
1600
1800
2000
PRX Pulse Width (us)
Figure 5. PRX400 Mode 0
25
47%, Hand, 1 Lux
20
47%, Hand, 300 Lux Fluorescent
47%, Hand, 300 Lux Incandescent
18% Gray Card, 1 Lux
Distance (cm)
92% White Card, 1 Lux
15
10
5
0
0
50
100
150
200
250
300
PRX Pulse Width (us)
Figure 6. PRX50 Mode 2
Rev. 1.0
9
Si11 20
40
35
30
18% Gray Card, 400 mA
Distance (cm)
25
18% Gray Card, 50 mA
92% White, 400 mA
92% White, 50 mA
20
15
10
5
0
0
200
400
600
800
1000
1200
1400
1600
PRX Pulse Width (us)
Figure 7. Combined PRX400 and PRX50
10
Rev. 1.0
1800
2000
Si1120
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 issue 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 different wavelength. The VAMB mode uses the visible
light photodiode which peaks at around 530 nm. On the other hand, the VIRH and VIRL modes use the photodiode
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, visible, and infrared light as a continuous spectrum.
The ratio between the visible and infrared photodiode readings provides a good clue 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 representative 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 are used as dividends 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 negative value). This rule-of-thumb can be used when accuracy is less critical.
Unless stated otherwise, the plots and figures used in this 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
Rev. 1.0
11
Si11 20
1
4000
0.9
3500
0.8
,OOXPLQDQFH/8;
3000
Normalized Response
0.7
0.6
0.5
VAMB
VIRL
0.4
2500
2000
1500
0.3
1000
0.2
500
0.1
0
0
400
0
400
500
600
700
800
900
800
1200
1600
2000
9$0%3XOVH:LGWK9$0%9,5+&RORU5DWLRa
1000
Wavelength (nm)
Figure 9. Si1120 Typical Spectral Response
Figure 12. Incandescent/Halogen Transfer
Function
100
2500
80
,OOXPLQDQFH/8/;
Illuminance (KLUX)
2000
60
40
1500
1000
20
500
0
0
100
200
300
400
500
600
0
700
0
50
100
VIRH Pulse Width (VIRL, VAMB saturated)
150
200
250
300
350
400
450
500
9$0%3XOVH:LGWK9$0%9,5/&RORU5DWLR!
Figure 10. Sunlight Transfer Function
Figure 13. CFL Transfer Function
140
4
3.5
3
100
/8;9$0%5DWLR
,OOXPLQDQFH/8;
120
80
60
40
2.5
2
1.5
1
0.5
20
0
10
0
0
200
400
600
800
1000
1200
1400
15
20
25
30
35
40
9$0%9,5+&RORU5DWLR
9,5/3XOVH:LGWK9,5/9$0%9,5/&RORU5DWLRa
Figure 14. Lux/VAMB vs. Color Ratio
Figure 11. Low Light Transfer Function
12
Rev. 1.0
Si1120
0.2
/8;9,5/5DWLR
0.16
0.12
0.08
0.04
0
0.04
0.05
0.06
0.07
0.08
0.09
0.1
9$0%9,5/&RORU5DWLR
Figure 15. Lux/VIRL Ratio vs. Color Ratio
Rev. 1.0
13
Si11 20
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 ambient-light noise. This added
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 noise
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 selfdischarge current of 10 µA, thus ensuring the battery's typical life of 10 years.
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.
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 capacitor. 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 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.
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.
14
Rev. 1.0
Si1120
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 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 Si1120 receiver, the
distance between the LED and the Si1120 should be maximized, and the distance between 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 taking a reference 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 can 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 measurement. The 'no object' reference measurement allows host software to establish the level
of system optical leakage and make the necessary corrections to account for this.
Transparent
window
PRX50
Mode
PRX400 Mode
In a similar way, for applications with heavy reliance on ALS accuracy, measurements using reference light sources
during factory calibration can be used to make adjustments to VAMB, VIRL, and VIRH measurements.
PRX50H Mode
Si1120
Si1120
Transmit LED
Optical block
Transmit LED
Internal Reflection Optical block
Single-port Optical Window
Dual-port Optical Window
Figure 16. Dual-Port and Single-Port Optical Window
Rev. 1.0
15
Si11 20
3. Pin Descriptions—Si1120 (ODFN)
PRX
1
8
VSS
TXGD
2
7
MD
TXO
3
6
SC
STX
4
5
VDD
Figure 17. Pin Configurations
Table 5. Pin Descriptions
16
Pin
Name
Description
1
PRX
2
TXGD
3
TXO
Transmit Output.
Normally connected to an infrared LED cathode. The output current is a programmable constant current sink. This output can be allowed to saturate, and output current can be limited by
the addition of a resistor in series with the LED.
4
STX
Strobe.
Initiates PS or ALS measurement. Also used as data input for the M2 internal mode control
flip-flop.
5
VDD
Power Supply.
2.2 to 3.7 V voltage source.
6
SC
Shutdown/Clock.
When high, shuts down the part. When enabling the part, the low-going edge clocks the states
of STX and MD into mode-control D flip-flops M2 and M3.
7
MD
Mode Control.
Controls two mode control bits, one directly and the other indirectly, by providing the data input
for the M3 internal mode control flip-flop.
8
VSS
VSS.
Ground (analog ground). Must be connected to TXGD.
PWM Output.
Outputs a low-going PWM pulse proportional to signal.
TXGD.
Power ground (LED and PRX driver ground return). Must be connected to VSS.
Rev. 1.0
Si1120
4. Ordering Guide
Part Ordering #
Temperature
Package
Si1120-A-GM
–40 to +85 °C
3x3 mm ODFN8
5. Photodiode Centers
Rev. 1.0
17
Si11 20
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
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.
18
Rev. 1.0
Si1120
DOCUMENT CHANGE LIST
Revision 0.41 to Revision 0.42


Removed custom package option.
Updated Table 1 on page 4.
Added

Added






Operating, Storage temps, and ESD to Table 1.
Updated "4. Ordering Guide" on page 17.
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 Modes" 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 Temperature 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 paragraph in "2.4. Ambient-Light
Modes" on page 11.
 Renamed Section “2.7. Mechanical and Optical
Implementation” to “2.7. Practical Considerations” .
Added

factory calibration guidance.
Added "5. Photodiode Centers" on page 17.
Rev. 1.0
19
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