LX1977
TM
®
SMBus Ambient Light Sensor
P
RODUCTION
D
ATASHEET
KEY FEATURES
Human Eye Spectral Response
Very Low IR Sensitivity
12-bit Resolution
5% Typical Accuracy
Rejection to 50/60Hz
Interference
Programmable Integration Time
Programmable Interrupt Pin
2
I C compatible SMBus Interface
Easy Processor Interface
No Optical Filter Needed
APPLICATIONS
Backlight Control for Notebook
Backlight Control for TV
Handheld Devices
Medical Devices
DESCRIPTION
The LX1977 is a CMOS based Ambient
Light Sensor (ALS) with an I
2
C compatible
SMBus interface.
This device is ideal for controlling
display back lighting systems of low cost
consumer products such as TV, portable
computers, handheld devices, or medical
devices. The LX1977 is optimized for a
linear, accurate, and very repeatable input
and output transfer function. The device also
features adjustable input range and gain.
The LX1977 has a spectral response
that emulates the human eye. Specially
designed circuitry produces peak spectral
response at 555 nm, with IR response less
than 10% above 810 nm.
Input dynamic range of this device is
adjustable via SMBus command. It can be set
to either 0 ~ 500 lux, 0 ~ 1000 lux, 0 ~ 2500
lux or 0 ~ 5000 lux.
Note: I
2
C is a trade mark of Philips
ALS internal compensation ensures
photodiode dark current are at very low
levels, providing high output accuracy at low
ambient light levels.
The LX1977 integrates a 12-bit Sigma-
Delta A/D converter that converts the ALS
photodiode output into a digital word. This
value is read via the I
2
C compatible SMBus
interface.
The LX1977 ALS is internally optimized
to an accuracy of approximately 5% over
temperature. The high accuracy and
repeatability of this device eliminates the
need of calibration during product
production, which results in reduced
assembly time and lower production cost.
The LX1977 is available in an 8-pin
MSOP package, and is operational over the
ambient temperature range -40˚C to 85˚C.
PACKAGE ORDER INFO
THERMAL DATA
T
A
(°C)
-40 to 85
DU
3 x 5 Glass Top MSOP 8-pin
RoHS Compliant / Pb-free
θ
JA
= 152
°C/W
THERMAL RESISTANCE
-
JUNCTION TO AMBIENT
LX1977IDU
ABSOLUTE MAXIMUM RATINGS
Note: Available in Tape & Reel. Append the letters “TR” to the part number.
(i.e. LX1977IDU -TR)
Junction Temperature Calculation: T
J
= T
A
+ (P
D
x
θ
JA
).
The
θ
JA
numbers are guidelines for the thermal performance of the
device/pc-board system. All of the above assume no ambient airflow.
PACKAGE PIN OUT
V
DD
............................................................................................................... -0.3 to 6V DC
Input Voltage to All Input Pins ........................................................... -0.3V to V
DD
+ 0.3V
SMBus Pin Voltage (SCL, SDA) .................................................................. -0.3V to 5.5V
SMBus Pin Current (SCL, SDA) ........................................................................... < 10 mA
Operating Temperature Range ........................................................................ -40 to +85°C
Storage Temperature Range.............................................................................-40 to 100°C
RoHS / Pb-free Peak Package Solder Reflow Temperature
(40 seconds maximum exposure).................................................................... 260° (+0, -5)
Notes: 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.
LX1977
LX1977
G
LASS
T
OP
MSOP 8 P
IN
(Top View)
RoHS / Pb-free 100% Matte Tin
Copyright
©
2010
Rev. 1.0, 2010-03-25
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1977
TM
®
SMBus Ambient Light Sensor
P
RODUCTION
D
ATASHEET
PRODUCT HIGHLIGHT
V
DD
V
DD
4000
LX1977 D
COUNT
vs LUX @ Fosc=40.96kHz, T
INT
=100mS
Vcc = 3.3V
V
DD
R
SET
ADR
3000
SDA
SCL
INT
Part
LX1977
V
SS
µP
V
SS
2000
0 ~ 500 lux
0 ~ 1000 lux
0 ~ 5000 lux
R
SET
1000
0 ~ 2500 lux
0
0
1000
2000
3000
LUX INPUT
4000
5000
6000
SIMPLIFIED BLOCK DIAGRAM
PACKAGE PHOTO
V
DD
V
DD
SDA
SCL
INT
ADR
V
SS
R
SET
Figure 1 –
Simplified Block Diagram
Figure 2 –
Product Photo
Pre
Amplifier
Sigma-
Delta
ADC
SMBus
Interface
FUNCTIONAL PIN DESCRIPTION
Name
V
DD
SDA
SCL
INT
ADR
R
SET
NC
V
SS
Pin #
1
2
3
4
5
6
7
8
PWR
Dir
PWR
I/O
I
O
I
I
Power Supply Voltage
SMBus Data – Connect To SMBus Data Line
SMBus Clock – Connect To SMBus Clock Line
Interrupt Output Pin, Active Low, Open Drain
SMBus Address – The Address For This Device Is Determined By The State Of This Pin.
ADR = GND sets address 20H, ADR = OPEN sets address 22H, ADR=V
DD
sets address 70H.
Gain Setting. For Gain Fine Adjustment. Typically, connect this pin to ground through a 1% 267k
resistor.
No Connection Pin
Ground Reference For Power And Signal Output
Description
LX1977
LX1977
Copyright
©
2010
Rev. 1.0, 2010-03-25
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1977
TM
®
SMBus Ambient Light Sensor
P
RODUCTION
D
ATASHEET
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C
≤
T
A
following test conditions: 3.0V
≤V
DD
≤
4.5V
Parameter
P
OWER
S
UPPLY
Operational Voltage
Supply Current
Supply Current
I
NTERNAL
Internal Oscillator Frequency
ALS R
ESPONSE
Peak Spectral Response
Infrared Response
Full Scale ADC Output Value
@ F
OSC
= 40.96kHz,
RANGE_SEL = 00b (0 ~ 500 lux)
RANGE_SEL = 01b (0 ~ 1000 lux)
RANGE_SEL = 10b (0 ~ 5000 lux)
RANGE_SEL = 11b (0 ~ 2500 lux)
Enable Time
Disable Time
Dynamic Response Time
ADC
Non-Linearity
ALS
ADC Output Count
@ F
OSC
= 40.96kHz, T
INT
= 50ms
RANGE_SEL = 01b (0 ~ 1000 lux)
ADC Output Count
@ F
OSC
= 40.96kHz, T
INT
= 100ms
RANGE_SEL = 00b (0 ~ 500 lux)
ADC Output Count
@ F
OSC
= 40.96kHz, T
INT
= 100ms
RANGE_SEL = 01b (0 ~ 1000 lux)
ADC Output Count
@ F
OSC
= 40.96kHz, T
INT
= 100ms
RANGE_SEL = 10b (0 ~ 5000 lux)
ADC Output Count
@ F
OSC
= 40.96kHz, T
INT
= 100ms
RANGE_SEL = 11b (0 ~ 2500 lux)
Dark ADC Count Value
Copyright
©
2010
Rev. 1.0, 2010-03-25
ELECTRICAL CHARACTERISTICS
≤
70°C and the
Max
4.5
0.2
15
Units
V
mA
µA
Symbol
V
DD
I
DD
I
DD
Note 5
Test Conditions / Comment
Min
3.0
Typ
Shut Down ALS
3.0V
≤V
DD
.≤ 3.6V
3.0V
≤V
DD
.≤ 4.5V
38.91
36.86
40.96
40.96
555
E
V(white)
= 100 lux, E
V(810nm)
= 14.6µW/cm ,
Note 3
T
INT
= 100 ms, Note 4
T
INT
= 50 ms, Note 4
T
INT
= 25 ms, Note 4
T
INT
= 6.25 ms, Note 4
Software Enable
Software Disable
Light Input Change From 200 lux to 20 lux
100
100
1
1
2
F
OSC
43.00
45.06
kHz
λ
PR(ALS)
Δ
IR
D
COUNT
D
COUNT
D
COUNT
D
COUNT
t
ON
t
OFF
T
F(90%~10%)
-8
nm
8
4095
2047
1023
255
µs
µs
ms
Counts
%
T
R(10%~90%)
Light Input Change From 20 lux to 200 lux
DNL
T
INT
= 100ms, RANGE_SEL=00b
Note 6
E
V
= 200 lux, Note 1,2
D
COUNT
E
V
= 500 lux, Note 1,2
E
V
= 1000 lux, Note 1,2
E
V
= 100 lux, Note 1,2
D
COUNT
E
V
= 200 lux, Note 1,2
E
V
= 500 lux, Note 1,2
E
V
= 200 lux
D
COUNT
E
V
= 500 lux
E
V
= 1000 lux
E
V
= 500 lux
D
COUNT
E
V
= 1000 lux
E
V
= 2000 lux
E
V
= 500 lux
D
COUNT
E
V
= 1000 lux
E
V
= 2000 lux
D
COUNT
E
V
= 0 lux, T
A
= 25°C, RANGE_SEL=00b,
T
INT
=100mS
-5
5
%
346
880
1768
692
1403
3537
372
931
1861
745
1489
3723
733
1808
3535
364
713
1437
734
1433
2851
0
398
982
1955
797
1575
3909
Counts
Counts
Counts
LX1977
LX1977
Counts
Counts
4
Counts
Page 3
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
LX1977
TM
®
SMBus Ambient Light Sensor
P
RODUCTION
D
ATASHEET
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C
≤
T
A
following test conditions: 3.0V
≤V
DD
≤
4.5V
Parameter
Symbol
Test Conditions / Comment
E
V
= 0 lux, T
A
= 70°C, RANGE_SEL=00b,
T
INT
=100mS, Note 7
Min
ELECTRICAL CHARACTERISTICS
≤
70°C and the
Max
18
Units
Typ
SMB
US
I
NTERFACE
Clock Frequency
High Level Input Voltage
Low Level Input Voltage
Input Leakage Current
SDA Low Output Voltage
SDA Current Sinking Capacity
INT Low Output Voltage
INT Leakage Current
ADR High Level Input Voltage
ADR Open
ADR Low Level Input Voltage
ADR Input Leakage Current
Notes:
1. In production, the input irradiance is supplied from a point source which is a white LED.
2. See Figure 3
3.
Δ
IR
=
D
COUNT
(E
V(WHITE)
+
E
V(IR)
)
−
D
COUNT
(E
V(WHITE)
)
F
CLK
V
SDA
V
SCL
I
SDA
/I
SCL
V
SDA
I
SDA
V
INT
I
LEAK
V
ADR
I
ADR
I
INT
= 3mA
I
SDA
= 3mA
10
0.8
400
2.1
kHz
V
V
µA
V
mA
V
µA
V
DD
V
DD
V
DD
µA
-5
3
5
0.4
0.4
-10
80%
40%
-10
10
60%
20%
10
D
COUNT
(E
V(WHITE)
)
4. Guarantee by scan tests.
5. Specifications in the EC table are for 3.0V ~ 4.5V. Device is operational down to 2.5V and up to 5.0V with relaxed specifications.
6. Gain1 = (D
COUNT
2-D
COUNT
1) / (Lux2-Lux1), Gain2 = (D
COUNT
3-D
COUNT
2) / (Lux3-Lux2), DNL1 = (Gain1 * 2 / (Gain1+Gain2) -1) %, DNL2 = (Gain2 *
2 / (Gain1+Gain2) – 1) %. Lux1 = 100 lux, Lux2 = 200 lux, Lux3 = 500 lux.
7. For the setting RANGE_SEL=00b and T
INT
=100mS, the full scale output is typical 3723 decimal. A dark ADC output count of maximum 18 at
T
A
= 70°C is only 0.5% of 3723.
TEST CIRCUITS
V
DD
V
DD
White
LED
R
SET
810nm
LX1977
LX1977
SDA
SCL
INT
Part
LX1977
ADR
To Test
Computer
V
SS
Figure 3 –
ALS Output Measurement
Copyright
©
2010
Rev. 1.0, 2010-03-25
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1977
TM
®
SMBus Ambient Light Sensor
P
RODUCTION
D
ATASHEET
APPLICATION NOTE
B
ASIC
F
UNCTIONALITY
The LX1977 is an ALS with an I C compatible SMBus
interface. It contains a high sensitivity close to human eye
response photodiode, a 12-bit Sigma-Delta ADC and a SMBus
interface. The Sigma-Delta ADC converts photodiode current to
digital values that correspond to the light incident on the
photodiode. The integrating nature of the ADC allows the device
to reject 50Hz and 60Hz flicker noise from environmental
lighting.
The Sigma-Delta ADC provides the flexibility to set different
conversion times, or integration time. It has four conversion
time selections to meet different application requirements. The
clock source for the ADC is also selectable from either an
internal clock or a SMBus clock. For internal clock selection,
the device features full speed (40.96kHz) and quarter speed
(10.24kHz) selection. The ADC conversion result is stored in a
12-bit register for read back even when another conversion is in
process.
SMBus I
NTERFACE
2
2
In this document, the device address is always expressed as
full 8 bit address. The high nibble of the address is from bit 7 to
bit 4. In the low nibble, bit 0 is always the R/W bit and in 8 bit
address format it is considered 0.
The address could be changed dynamically. The requirement is
that after the change, the LX1977 ALS should be disabled and
then enabled either via bit 6 of register 00h or a V
DD
power cycle.
Table 2: Address = 20h
1
S
7
Slave Address
0010000
1
Wr
0
1
A
8
Data Byte
1
A
1
P
Table 3: Address = 22h
1
S
7
Slave Address
0010001
1
Wr
0
1
A
8
Data Byte
1
A
1
P
LX1977 is a nine-register device which uses SMBus or I C
1
7
1
1
8
1
1
protocols to communicate with the host system. All registers
S
Slave Address
Wr
A
Data Byte
A
P
are defined as full byte wide. Some registers contain reserved
(undefined) bits with a default value of “0”, or are read only bits
0111000
0
that are status indicators. Six of the nine registers are capable of
both read and write, and three registers are read only. See the
SMBus P
ROTOCOL
LX1977 Register Definitions section for details.
The only required command protocols are SMBus Send Byte,
The LX1977 communicates over the SMBus and operates in
a “slave” mode receiving commands and sending / receiving Receive Byte, Read Byte / Word, and the Write Byte / Word
data to / from the host or “master”. Only standard two-wire protocols. See Table 7 ~ Table 12 for details.
SMBus and I
2
C compatible serial bus and protocols may be
used for this device. The LX1977 can be configured for one of
the three addresses by connecting the ADR input pin to ground,
V
DD,
or simply leaving it OPEN.
Writes to registers can be performed by either the SMBus
Write Byte / Word protocols and / or by internal IC logic,
depending on the register type (see Table 13). Send Byte
protocol can only be used on the Command / Status register
(register 00h).
Read can be performed on all registers by issuing the Read
Byte / Word protocol. Note that Receive Byte protocol can only
be used on the Command / Status register (register 00h) for a
quick test of the status bits. Read Only registers can be written
only by internal logics. Their contents will not be affected by
SMBus write commands.
When LX1977 is initially powered, it will first test the
address selection pin input to determine its own address and then
look for its unique address each time it detects a “Start
Condition”. If the address does not match, the LX1977 ignores
all bus activity until it encounters another “Start Condition”. If
the address is a match, the LX1977 acknowledges that it has
detected its address and a W/R bit to either read or write. If the
Table 4: Address = 70h
Table 1: Address strapping codes
Option #
ADR
Hex Address
GND
20h
1
OPEN
22h
2
V
DD
70h
3
LX1977
LX1977
Copyright
©
2010
Rev. 1.0, 2010-03-25
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
Microcontroller MCU
京公网安备 11010802033920号
EEWORLD
