Microsemi LX1974IBC Ambient light detector Datasheet

LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
Dynamic range is determined by the
resistors (typically in the range of 10K
to 100K) and power supply values.
Typically the LX1974 needs only 1.8V
of headroom to operate at 1000 Lux
illumination.
Internal temperature compensation
allows dark current to be kept below
200nA over the full specification
temperature range (-40 to +85°C),
providing high accuracy at low light
levels. Usable ambient light conditions
range is from 1 to more than 5000 Lux.
The LX1974 is optimized for
controlling back lighting systems in low
cost consumer products such as LCD
TV, portable computers, and digital
cameras.
ƒ Near Human Eye Spectral
Response
ƒ Very Low IR Sensitivity
ƒ Highly Accurate & Repeatable
Output Current vs. Light
ƒ Scalable Output Voltage
ƒ Temperature Stable
ƒ Integrated High Gain Photo
Current Amplifiers
ƒ No Optical Filters Needed
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The LX1974 is a low cost silicon
light sensor with spectral response that
closely emulates the human eye.
Patented circuitry produces peak
spectral response at 520nm, with IR
response less than ±5%, of the peak
response, above 900nm.
The photo sensor is a PIN diode array
with a linear, accurate, and very
repeatable current transfer function.
High gain current mirrors on the chip
multiply the PIN diode photo-current
to a sensitivity level that can be
voltage scaled with a standard value
external resistor. Output current from
this simple to use two-pin device can
be used directly or converted to a
voltage by placing it in series with a
single resistor at either of its two pins.
APPLICATIONS
ƒ
ƒ
ƒ
ƒ
ƒ
Portable Electronic Displays
LCD TV Backlight Systems
Digital Still Cameras (DSC)
Desktop Monitors
Notebook Computers
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
Protected By U.S.Patents: 6,787,757; Patents Pending
PRODUCT HIGHLIGHT
LX1974
LIGHT
LX1974
PACKAGE ORDER INFO
TA (°C)
BC
Plastic 1206
2-Pin
RoHS Compliant / Pb-free
-40 to 85
LX1974IBC
Note: Available in Tape & Reel. Append the
letters “TR” to the part number.
(i.e. LX1974IBC-TR)
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
VDD
VSS
2
1
BC PACKAGE
(Top View)
RoHS / Pb-free Gold Lead Finish
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
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Supply Input Voltage ...........................................................................-0.3V to 6V
Ground Current ..........................................................................Internally Limited
Operating Temperature Range .........................................................-40°C to 85°C
Maximum Operating Junction Temperature ................................................ 150°C
Storage Temperature Range.........................................................-40°C to +100°C
RoHS / Pb-free Peak Package Solder Reflow Temperature
(40 second maximum exposure) ..................................................... 260°C (+0, -5)
THERMAL DATA
BC
Plastic 1206 2-Pin
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA
850°C/W
Junction Temperature Calculation: TJ = TA + (PD x θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the
above assume no ambient airflow.
FUNCTIONAL PIN DESCRIPTION
Name
Description
VDD
Positive Terminal
VSS
Negative Terminal
CHARACTERISTIC CURVES
PACKAGE DATA
Chart 1 & 2 – Step Response Graphs
VDD = 4V, 200 to 20 Lux step 30.3K Load resistance
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
CHARACTERISTIC CURVES
Operating Voltage
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2.5
2.0
1.5
1.0
10µA
100µA
200µA
0.5
0.0
-40
-20
0
20
40
60
80
Temperature (°C)
Chart 4 – Typical Operating Voltage Vs VSS Current
Dark Current (nA)
300
250
200
150
100
50
0
-40
-20
0
20
40
60
80
100
Temperature (°C)
Chart 3 – Response vs. wavelenght
Chart 5 – Dark Leakages Vs. Temperature
IOUT @ 1000 LUX, VDD=5.0V, 10K LOAD
150
140
130
120
UA
110
100
90
80
70
-40
-20
0
20
40
60
80
CHARTS
60
-60
100
Temperature
Chart 6 – Typical Temperature Response
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
ELECTRICAL CHARACTERISTICS
Parameter
`
Symbol
Test Conditions
≤
85°C except where
LX1974
Typ
Min
Max
Units
RESPONSE
λPR
Peak Spectral Response
Infrared Response
IDD (λ )
IDD (λ PR )
Minimum Operational Voltage
VDD-VSS
Light Current
ISS
Gain Linearity
Dark Current
IDD(DARK)
Power Supply Rejection Ratio
Radiant Sensitive Area
PSRR
2
EV(550nm) = 292μW/cm , Current responsivity
change with additional direct light input of
292μW/cm2 at 910nm, Note 3
EV = 14.6μW/cm2, ISS = 10μA
EV = 146μW/cm2, ISS = 100μA
EV = 292μW/cm2, ISS = 200μA
EV = 14.6μW/cm2 (100 lux), Note 2
EV = 146μW/cm2 (1K lux), Note 2
2
EV = 292μW/cm (2K lux), Note 2
2
14.6μW/cm ≤ EV ≤ 146μW/cm2 @ 25°C
EV = 0μW/cm2, TA = 25°C
EV = 0μW/cm2
VRIPPLE = 10mVP-P, f = 10kHz
520
-5
7.5
75
150
-15
nm
1
5
1.2
1.8
2.2
10
100
200
1.4
2.1
2.6
12.5
125
250
15
50
200
0.010
-25
0.04
%
V
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Unless otherwise specified, the following specifications apply over the operating ambient temperature -40°C ≤ TA
otherwise noted and the following test conditions: See Note 1, VDD =5V, RSS = 10K
μA
%
nA
dB
mm2
Notes:
1. The input irradiance (EV) is supplied from a white light-emitting diode (LED) optical source adjusted to impose the specified EV at a
peak λ = 550nm.
2. See Figure 1.
3. See Figure 2.
TEST CIRCUITS
VDD
VDD
LX1974
LX1974
White
LED
VSS
White
LED
10kΩ
VSS
10kΩ
ELECTRICALS
Figure 1 – Operational Voltage Measurement Circuit
Copyright © 2005
Rev. 1.0, 2006-05-09
910nm
Figure 2 – IR Sensitivity Measurement Circuit
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
SIMPLIFIED BLOCK DIAGRAM
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VDD
Current
Amp
VSS
Figure 3 – Simplified Block Diagram
APPLICATION NOTE
LIGHT UNITS
2
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
APPLICATIONS
In converting from µW/cm to lux it is necessary to
define the light source. Lux is a unit for the measurement
of illuminance, which is the photometric flux density or
visible light flux density.
Whereas µW/cm2 is a
measurement of irradiance or the measurement of
electromagnetic radiation, flux both visible and invisible.
The first step in the conversion process is to convert
irradiance to illuminance, which essentially involves
running the irradiant flux through a photopic filter. In
normal ambient, a photopic curve is used and in dark
ambient, a scotopic curve (dark adapted eye) is used. If
the light is composed of only one wavelength, a
conversion chart will tell the conversion factor to convert
µW/m2 to lux (lumens/m2). If more than one wavelength
is used, the light spectrum of the irradiance must be
applied to the photopic filter to determine the resultant
illuminance. The most sensitive wavelength for the
normal light adapted human eye is 555nm, which
corresponds to yellowish-green light. At 555nm, the
conversion factor is 683 Lux = 1W/m2 = 100µW/cm2.
Therefore 14.6µW/cm2 = 100 lux at 555nm.
If the photo sensor had a truly photopic response, it would
produce the same output current for the same number of lux,
regardless of the color of the light. However, because the
match is not perfect, there is still wavelength dependency
particularly at the ends of the visible spectrum.
In the case of the LX1974 the peak photo response is at
520nm, however depending on the light source, what the
human eye perceives as ‘white’ light may actually be
composed of peak wavelengths of light other than 520nm.
For instance, a typical fluorescent lamp includes dominant
light not only near 550nm but also at 404 and 435nm.
Incandescent light sources such as standard tungsten lights
generate substantial IR radiation out beyond 2000nm.
For ease of automatic testing of the LX1974 the ATE
(automatic test equipment) light source is configured with
white LED’s whose current is adjusted to output a calibrated
flux density at 550nm. This allows consistent and repeatable
testing of the sensor but corresponds to a light source unlike
that typically found in an office, home or sunlit environment.
In practice, the user needs to place the sensor in the target
environment and calibrate the sensors output current range to
match the application objective. This is easily accomplished
by adjusting the output resistor, which sets the sensor’s gain.
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
APPLICATION EXAMPLES
The output node will actually reach 1.25V when the source
current from the LX1974 is only about 44µA since about
6µA of current will be contributed from R1. This assumes a
high impedance input to the LED driver. In Figure 5, user
adjustable bias control has been added to allow control over
the minimum and maximum output voltage. This allows the
user to adjust the output brightness to personal preference
over a limited range. In addition, an equivalent DC voltage
may replace the PWM input source.
3.3V or 5V
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The following examples present both fully automatic
(no user input) and semi-automatic to fully manual
override implementations. These general guidelines are
applicable to a wide variety of potential light control
applications. The LX1974 can be used to control the
brightness input of CCFL inverters (like Microsemi’s
PanelMatch™ inverter family, or line of controller IC’s).
Likewise, it can interface well with LED drivers like the
LX1990 and LX1991 sink LED drivers, or boost drivers
like the LX1992, LX1993, LX1994, and LX1995.
In each specific application, it is important to recognize
the need to correlate the output current of the LX1974 for
the target environment and its ambient light conditions.
The mechanical mounting of the sensor, light aperture
hole size, use of a light pipe or bezel are critical in
determining the response of the LX1974 for a given
exposure of light.
VDD
VSS
3.3V PWM
3.3V or 5V
R1
40K
To inverter
brightness input or
LED driver
10µF controller input.
R2
25K
VDD
VSS
3V
R1
R2
Figure 5 – Semi-Manual Controlled Dimming
To inverter brightness
input or LED driver
controller.
C1
Figure 6 shows how a fully manual override can be quickly
added to the example in figure 5. In addition to the gate to
turn on and off the LX1974, a diode has been inserted to
isolate the sensor when it is disabled.
10µF
Disable
control
Figure 4 – Fully Automatic Dimming
CMOS
Gate
The example in figure 4 shows a fully automatic
dimming solution with no user interaction. Choose R1
and R2 values for any desired minimum brightness and
slope. Choose C1 to adjust response time to filter 50/60
Hz room lighting. As an example, let’s say you wish to
generate an output voltage from 0.25V to 1.25V to drive
the input of an LED driver controller. The 0.25V
represents the minimum LED brightness and 1.25V
represents the maximum. The first step would be to
determine the ratio of R1 and R2.
VSS
3.3V
60K
PWM
30K
R1 = R2 ⎢
Copyright © 2005
Rev. 1.0, 2006-05-09
10µF
30K
To inverter
brightness input or
LED driver
controller.
Figure 6 – Fully Manual Controlled Dimming
The preceding examples represent just a few of the
potential sensor applications. Further details and additional
circuits can be found in the application note (AN-28) LX1970
Visible Light Sensor located in the application section of
Microsemi’s website: www.microsemi.com. Although this
application note is written around the LX1970 visible light
sensor the circuits can be easily adapted for use with the
LX1974.
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
APPLICATIONS
⎤
⎡ 3.0V
− 1⎥ = 11 × R2
0.25V
⎦
⎣
Next the value of R2 can be calculated based on the
maximum output source current coming from the
LX1974 under the application’s maximum light exposure,
lets say this has been determined to be about 50µA .
Thus R2 can be calculated; first order as follows:
⎡1.25V ⎤
R2 = ⎢
= 25KΩ ∴ R1 = 11 × R2 = 275KΩ
⎣ 50µA ⎥⎦
VDD
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
APPLICATION CIRCUITS
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D1
UPS5817
L1 10µH
VIN
IN
GND
C2
1µF
SW
SHDN
C1
4.7µF
BACKLIGHT
LX1995
R1
100K
FB
GND
R5
5.76K
SHDN
R4
10K
R7
24.9K
MMBT2907
R8
60.4K
3.3V
LX1974
VSS
R6
15
C3
10µF
R10
49.9K
C4
0.1µF
VDD
Figure 7 – Typical Application with Microsemi’s LX1995 LED Driver IC
22µH
UPS5819
VIN = 2.0V to 5.5V
FDN337
PWM Dimming Input
3.3V
4.99K
LX1974
VDD
VSS
MMBT2907
15K
VIN
DRV
S/P
SRC
BRT
OVP
LS
GND
22µF
100K
1µF
LX1994
1µF
1M
FB
CMP
41.2K
15
APPLICATIONS
0.1µF
178K
Figure 8 – Typical Application with Microsemi’s LX1994 LED driver IC
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1974
®
TM
Ambient Light Detector
P RODUCTION D ATA S HEET
PACKAGE DIMENSIONS
2-Pin 1206 Standard Carrier
D
Dim
A
B
C
D
E
H
Θ
P
R
X
Sensor Active
Area: 0.2 x 0.2mm
CL
2
P
C
R
CL C
0.03
2
1
Top
E
Sensor Active Area
θ
0.19 - 0.25mm
B
A
1
Bottom
H
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BC
Side
Pin 1 Indicator (top side) /
Alignment Indicator (Bottom side)
X
MILLIMETERS
MIN
MAX
0.95
1.25
0.40
0.70
0.90
1.10
3.05
3.35
1.90
2.10
0.40
0.60
3° nom
1.45
1.75
0.25 nom
0.02
0.05
INCHES
MIN
MAX
0.037 0.049
0.016 0.028
0.035 0.043
0.120 0.132
0.075 0.083
0.016 0.024
3° nom
0.057 0.069
0.010 nom
0.001
0.002
Note:
Dimensions do not include protrusions; these shall not excee
0.155mm (.006”) on any side.
Recommended Soldering Pattern for reflow soldering of the
BC (1206) package.
1.50mm
0.06in.
1.50mm
0.06in.
2.0mm
0.08in.
1.50mm
0.06in.
Super Imposed
1206 Package
Basic specification is < 5 seconds @ 260°C when applying
solder.
Lead In: 10 min empty
Loaded: 3000 pcs
Lead Out: 40 min empty
4.00
1.75
5.25
8.00
MECHANICALS
0.20
2.00
4.00
1.30
Note: LX1974 parts are loaded bottom side up
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1974
TM
®
Ambient Light Detector
P RODUCTION D ATA S HEET
NOTES
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NOTES
PRODUCTION DATA – Information contained in this document is proprietary to
Microsemi and is current as of publication date. This document may not be modified in
any way without the express written consent of Microsemi. Product processing does not
necessarily include testing of all parameters. Microsemi reserves the right to change the
configuration and performance of the product and to discontinue product at any time.
Copyright © 2005
Rev. 1.0, 2006-05-09
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
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