19-5284; Rev 2; 5/11
TION KIT
EVALUA BLE
IL
AVA A
Industry’s Lowest-Power
Ambient Light Sensor with ADC
Features
The MAX9635 ambient light sensor features an I2C digi-
S Wide 0.045 Lux to 188,000 Lux Range
tal output that is ideal for a number of portable applications such as smartphones, notebooks, and industrial
sensors. At less than 1µA operating current, it is the
lowest power ambient light sensor in the industry and
features an ultra-wide 22-bit dynamic range from 0.045
lux to 188,000 lux.
S Small, 2mm x 2mm x 0.6mm OTDFN
S VCC = 1.7V to 3.6V
S ICC = 0.65µA Operating Current
S -40NC to +85NC Temperature Range
Low-light operation allows easy operation in dark glass
applications.
The on-chip photodiode’s spectral response is optimized
to mimic the human eye’s perception of ambient light
and incorporates IR and UV blocking capability. The
adaptive gain block automatically selects the correct lux
range to optimize the counts/lux.
The IC is designed to operate from a 1.7V to 3.6V supply voltage range and consumes only 0.65µA in full
operation. It is available in a small, 2mm x 2mm x 0.6mm
OTDFN package.
Ordering Information
PART
PIN-PACKAGE
TEMP RANGE
MAX9635EDT+
6 OTDFN-EP*
-40NC to +85NC
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Applications
Block Diagram
Tablet PCs/Notebook Computers
TVs/Projectors/Displays
VCC
Digital Lighting Management
Portable Devices
Cellular Phones/Smartphones
VISIBLE +IR
PHOTODIODE
Security Systems
MAX9635
IR
PHOTODIODE
SDA
16-BIT
ADC
6-BIT RANGE
CDR, TIM
CONTROL
SCL
I2C
AO
DIGITAL
SIGNAL
PROCESSING
INT
16-BIT
ADC
N
GND
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX9635
General Description
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
ABSOLUTE MAXIMUM RATINGS
INT to GND................................................ -0.3V to (VCC + 0.3V)
All Other Pins to GND..............................................-0.3V to +4V
INT Short-Circuit Current Duration......................................... 10s
All Other Pins Short-Circuit Current Duration.............Continuous
Continuous Input Current into Any Terminal.................... Q20mA
Continuous Power Dissipation
6 OTDFN (derate 11.9mW/NC above +70NC)...............953mW
Operating Temperature Range........................... -40NC to +85NC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = 1.8V, TMIN to TMAX = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
OPTICAL CHARACTERISTICS
Maximum Lux Sensitivity
Fluorescent light
Saturation Ambient Lux Level
Sunlight
Total Error
TE
Light Source Matching
0.045
Lux/LSB
188,000
Lux
Green LED 538nm response,
TA = +25NC (Note 2)
15
Fluorescent/incandescent light
10
Infrared Transmittance at 940nm
IRR
TA = +25NC (Note 3)
0
Ultraviolet Transmittance at
363nm
UVR
TA = +25NC (Note 3)
1.2
Dark Level Count
0LUX
0 lux, TA = +25NC, 800ms range
Maximum Signal Integration
Time
0
Has 50/60Hz rejection
Minimum Signal Integration Time
ADC Conversion Time
%
0.5
100
Manual mode only
6.25
100
103
ACT
100ms range, TA = +25NC
100ms range
99.6
97
VCC
Guaranteed by TE test
1.7
%
%
0.045
800
Automatic mode, has 50/60Hz rejection
%
Lux
ms
ms
100.4
107
ms
3.6
V
POWER SUPPLY
Power-Supply Voltage
Power-Supply Current
ICC
TA = +25NC, 90 lux,
I2C
0.65
inputs inactive
1.2
1.6
TA = -40NC to +85NC
FA
DIGITAL I/O CHARACTERISTICS
VOL
Output Low Voltage SDA, INT
INT Leakage Current
SCL, SDA, A0 Input Current
IIH, IIL
ISINK = 6mA
0.06
0.4
V
TA = +25NC
0.01
20
nA
TA = +25NC
0.01
20
nA
0.3 x
VCC
V
I2C Input Low Voltage
VIL_I2C
SDA, SCL
I2C Input High Voltage
VIH_I2C
SDA, SCL
Address Input Low Voltage
VIL_A0
A0
Address Input High Voltage
VIH_A0
A0
Input Capacitance
2
0.7 x
VCC
V
0.3
VCC 0.3V
V
V
3
pF
Industry’s Lowest-Power
Ambient Light Sensor with ADC
MAX9635
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 1.8V, TMIN to TMAX = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
400
kHz
I2C TIMING
Serial-Clock Frequency
fSCL
Bus Free Time Between a STOP
and a START Condition
tBUF
1.3
Fs
Hold Time (REPEATED) START
Condition
tHD,STA
0.6
Fs
Low Period of the SCL Clock
tLOW
1.3
Fs
High Period of the SCL Clock
tHIGH
0.6
Fs
Setup Time for a Repeated
START Condition
tSU,STA
0.6
Fs
Data Hold Time
tHD,DAT
(Note 4)
Data Setup Time
tSU,DAT
Fall Time of SDA Transmitting
Setup Time for STOP Condition
Pulse Width of Spike
Suppressed
tF
0.9
100
ISINK P 6mA, tR and tF are measured
between 0.3 x VDD and 0.7 x VDD
tSU,STO
tSP
0
ns
100
ns
0.6
Input filters on the SDA and SCL inputs
suppress noise spikes
0
Fs
Fs
50
ns
Note 1: All devices are 100% production tested at TA = +25NC. Temperature limits are guaranteed by design.
Note 2: Guaranteed by design. Green 538nm LED chosen for production so that the IC responds to 100 lux fluorescent light with
100 lux.
Note 3: With respect to green LED 538nm response.
Note 4: A master device must provide a hold time of at least 300ns for the SDA signal (referred to VIL of the SCL signal) to bridge
the undefined region of SCL’s falling edge.
3
Typical Operating Characteristics
(VCC = 1.8V, default power upsetting; unless otherwise noted.)
SPECTRUM RESPONSE
RADIATION PATTERN
MAX9635 RESPONSE
80
60
40
CIE
20
MAX9635 toc02
90
80
70
60
50
40
30
AUTO MODE,
INCANDESCENT LAMP
20
10
0
0
400
500
600
700
800
900
-90
1000
-60
-30
SPECTRUM OF LIGHT SOURCES
FOR MEASUREMENT
MAX9635 toc03
120
SUNLIGHT
80
60
40
FLUORESCENT
1.0
400
500 600 700 800
WAVELENGTH (nm)
0.8
0.6
100 LUX, CONT = 0
0.4
1.02
1.00
0.98
0.96
0.94
50 AND 300 LUX
AUTO MODE,
FLUORESCENT LAMP
0.92
0.90
1.5
1.8
2.1
2.4
2.7
3.0
SUPPLY VOLTAGE (V)
2.4
2.7
3.0
3.3
3.6
SUPPLY CURRENT vs. TEMPERATURE
VCC = 3.3V
1.0
SUPPLY CURRENT (µA)
1.04
2.1
1.2
MAX9635 toc05
1.06
1.8
SUPPLY VOLTAGE (V)
OUTPUT CODE ERROR vs. SUPPLY VOLTAGE
1.08
AUTO MODE,
FLUORESCENT LAMP
1.5
900 1000
1.10
4
5000 LUX, CONT = 0
0
0
300
90
0 LUX AND 100 LUX, CONT = 1
0.2
20
60
1.2
SUPPLY CURRENT (µA)
NORMALIZED RESPONSE
INCANDESCENT
100
30
SUPPLY CURRENT vs. SUPPLY VOLTAGE
1.4
160
140
0
LUMINOSITY ANGLE (°)
WAVELENGTH (nm)
MAX9635 toc04
300
MAX9635 toc06
NORMALIZED RESPONSE
100
100
RELATIVE SENSITIVITY (% FROM 0°)
MAX9635 toc01
120
OUTPUT CODE ERROR (RATIO FROM 1.8V)
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
0.8
0.6
VCC = 2.5V
VCC = 1.8V
0.4
100 LUX
AUTO MODE,
FLUORESCENT LAMP
0.2
0
3.3
3.6
-40
-15
10
35
TEMPERATURE (°C)
60
85
Industry’s Lowest-Power
Ambient Light Sensor with ADC
SUPPLY CURRENT vs. LUX READING
2.0
1.5
1.0
200
INCANDESCENT
LAMP
150
100
50
0.5
SUNLIGHT
0
0
100
1k
10k
100k
0
LUX READING (LUX)
50
100
150
200
250
300
REFERENCE METER READING (LUX)
120
110
100
90
80
70
60
50
40
30
20
10
0
MAX9635 toc09
MAX9635 toc08
250
VOL (mV)
2.5
FLUORESCENT
LAMP
300
MAX9635 READING (LUX)
3.0
SUPPLY CURRENT (µA)
350
MAX9635 toc07
3.5
SDA, INT OUTPUT LOW VOLTAGE
vs. SINK CURRENT
LIGHT SENSITIVITY vs. LUX LEVEL
SDA
INT
0
1
2
3
4 5 6
ISINK (mA)
7
8
9
10
Pin Configuration
TOP VIEW
SDA
SCL
INT
6
5
4
MAX9635
+
EP
1
2
3
VCC
GND
A0
OTDFN
(2mm x 2mm)
Pin Description
PIN
NAME
1
VCC
Power Supply
FUNCTION
2
GND
Ground
3
A0
4
Interrupt Output. Use an external pullup resistor.
5
INT
SCL
6
SDA
I2C Data Bus
—
EP
Address Select. Pull high to select address 0x96 or low to select address 0x94.
I2C Clock Bus
Exposed Pad. Connect EP to ground.
5
MAX9635
Typical Operating Characteristics (continued)
(VCC = 1.8V, default power upsetting; unless otherwise noted.)
Detailed Description
The default integration time of the ADC is 100ms, giving
it inherent rejection of 50Hz and 60Hz ripple common in
certain line-powered light sources.
The MAX9635 is an ambient light sensor with integrated
photodiode and ADC with an I2C digital interface. To
measure ambient light, the die is placed inside an
optically transparent (OTDFN) package. A photodiode inside the IC converts the light to a current that is
then processed by low-power circuitry into a digital bit
stream. This is digitally processed and stored in an output register that is read by an I2C interface. An on-chip
programmable interrupt function eliminates the need for
continually polling the device for data and results in significant power saving.
Human Eye CIE Curve and
Different Light Sources
The IC is designed to detect brightness in the same way
as human eyes do. To achieve this, the sensor needs to
have a spectral sensitivity that is similar to that of human
eyes. Figure 1 shows the spectral sensitivity of the IC
and the human eye (CIE curve).
As can be seen, the human eye has its peak sensitivity
at 555nm (green), while that of blue (~470nm) and red
(~630nm) is much lower. The human eye also is blind to
infrared (> 700nm) and ultraviolet (< 400nm) radiation.
Light sources can have similar visible brightness (lux), but
different IR radiation content (because the human eye is
blind to it). The differences in the light spectra affect brightness measurement because some of this infrared radiation
is picked up by silicon photodiodes. For example, light
sources with high IR content, such as an incandescent
bulb or sunlight, would suggest a much brighter environment than our eyes would perceive them to be. Other light
sources, such as fluorescent and LED-based systems,
have very little infrared content. The IC exhibits good IR
rejection and internal IR compensation scheme to minimize
these effects and give an accurate lux response.
A package-level optical filter prevents ultraviolet
and infrared from reaching the photodiode. Its optical response is also designed to match the spectral
response of the human eye. A second photodiode array,
sensitive primarily to the infrared spectrum, is then used
to match flourescent and incandescent light response
from the part.
Two key features of the IC analog design are its ultra-low
current consumption (typically 0.65µA) and an extremely
wide dynamic light range that extends from 0.045 lux to
188,000 lux—more than a 4,000,000 to 1 range. The onchip autoranging scheme requires no user intervention
for the gain-range setting.
The IC can be customized to operate at enhanced sensitivity in applications where it needs to operate behind
a dark glass.
120
100
NORMALIZED RESPONSE
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
MAX9635 RESPONSE
80
60
40
CIE
20
0
300
400
500
600
700
800
WAVELENGTH (nm)
Figure 1. Spectral Sensitivity of the MAX9635 and Human Eye
6
900
1000
Industry’s Lowest-Power
Ambient Light Sensor with ADC
Table 1. Register Map
BIT
REGISTER
REGISTER
ADDRESS
POWER-ON
RESET
STATE
R/W
7
6
5
4
3
2
1
0
Interrupt Status
—
—
—
—
—
—
—
INTS
0x00
0x00
R
Interrupt Enable
—
—
—
—
—
—
—
INTE
0x01
0x00
R/W
CONT
MANUAL
—
—
CDR
0x02
0x03
R/W
Lux High Byte
E3
E2
E1
E0
M7
M6
M5
M4
0x03
0x00
R
Lux Low Byte
—
—
—
—
M3
M2
M1
M0
0x04
0x00
R
Upper Threshold
High Byte
UE3
UE2
UE1
UE0
UM7
UM6
UM5
UM4
0x05
0xFF
R/W
Lower Threshold
High Byte
LE3
LE2
LE1
LE0
LM7
LM6
LM5
LM4
0x06
0x00
R/W
Threshold Timer
T7
T6
T5
T4
T3
T2
T1
T0
0x07
0xFF
R/W
STATUS
CONFIGURATION
Configuration
TIM[2:0]
LUX READING
THRESHOLD SET
Interrupt Status 0x00
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
—
—
—
—
—
—
—
INTS
0x01
If the INTE bit is set to 1, then the INTS status bit is asserted if the light intensity exceeds either upper or lower threshold
limits (as specified by registers 0x05 and 0x06, respectively) for a period longer than that defined by the Threshold
Timer register (0x07). This bit resets to 0 after the host reads this register. See Table 2.
This bit is also reflected on the INT pin. When the INTS bit is set, the INT pin is asserted low, and when the INTS bit is
set to 0, the INT pin is pulled high by an external resistor.
Once this bit is set, it can be cleared either by reading the Interrupt Status register 0x00 or by writing a 0 to the Interrupt
Enable register 0x01.
Table 2. Interrupt Status Register
BIT 0
OPERATION
0
No interrupt trigger event has occurred.
1
Ambient light intensity is outside the threshold window range for a longer than specified time.
Interrupt Enable 0x01
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
—
—
—
—
—
—
—
INTS
0x01
7
MAX9635
Register and Bit Descriptions
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
Interrupt events set the INTS bit (register 0x00, bit 0) and the INT pin only if the INTE bit is set to 1. If the INTE bit is set
(interrupt is enabled) and the interrupt condition is triggered, then the INT pin is pulled low (asserted) and the INTS bit
in the Interrupt Status register is set to 1. See Table 3.
Table 3. Interrupt Enable Register
BIT 0
OPERATION
0
The INT pin and the INTS bit are not asserted even if an interrupt event has occurred.
1
Detection of an interrupt event triggers a hardware interrupt (INT pin is pulled low) and sets the INTS bit
(register 0x00, bit 0).
Configuration 0x02
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
CONT
MANUAL
—
—
CDR
BIT 2
BIT 1
BIT 0
TIM[2:0]
REGISTER
ADDRESS
0x02
Continuous Mode
Table 4. Continuous Mode Register
BIT 7
OPERATION
0
Default mode. The IC measures lux intensity only once every 800ms regardless of integration time. This
mode allows the part to operate at its lowest possible supply current.
1
Continuous mode. The IC continuously measures lux intensity. That is, as soon as one reading is finished, a
new one begins. If integration time is 6.25ms, readings are taken every 6.25ms. If integration time is 800ms,
readings are taken every 800ms. In this mode, the part consumes slightly higher power than in the default
mode.
Note: Continuous mode is independent of the manual configuration mode setting.
Manual Configuration Mode
In automatic mode (MANUAL = 0), reading the contents of TIM[2:0] and CDR bits reflects the automatically generated
values from an internal timing register and are read-only. In manual mode (MANUAL = 1), the contents of TIM[2:0] and
CDR bits can be modified by the users through the I2C bus.
Table 5. Manual Configuration Register
BIT 6
OPERATION
0
Default mode of configuration is used for the IC. In this mode, CDR and TIM[2:0] bits are automatically determined by the internal autoranging circuitry of the IC.
1
Manual mode of configuration is used for the IC. In this mode, CDR and TIM[2:0] bits can be programmed
by the user.
Current Division Ratio (CDR)
The CDR bit controls the current division ratio. The photodiode current is divided as shown in Table 6.
Table 6. Current Division Ratio Register
BIT 3
8
OPERATION
0
Current not divided. All of the photodiode current goes to the ADC.
1
Current divided by 8. Only 1/8 of the photodiode current goes to the ADC. This mode is used in
high-brightness situations.
Industry’s Lowest-Power
Ambient Light Sensor with ADC
In automatic mode (MANUAL = 0), integration time is automatically selected by the on-chip algorithm to be either
100ms/200ms/400ms/800ms. In manual mode (MANUAL = 1), integration time can be varied by the user all the way
from 6.25ms to 800ms. See Table 7.
Table 7. Integration Time
TIM[2:0]
INTEGRATION
TIME (ms)
000
800
This is a preferred mode for boosting low-light sensitivity.
001
400
—
010
200
—
011
100
This is a preferred mode for high-brightness applications.
100
50
Manual mode only.
101
25
Manual mode only.
110
12.5
Manual mode only.
111
6.25
Manual mode only.
COMMENTS
Lux High-Byte Register 0x03
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
E3
E2
E1
E0
M7
M6
M5
M4
0x03
Bits in Lux High-Byte register 0x03 give the 4 bits of exponent E3:E0 and 4 most significant bits of the mantissa byte
M7:M4, and represent the lux reading of ambient light. The remaining 4 bits of the mantissa byte M3:M0 are in the Lux
Low-Byte register 0x04 and enhance resolution of the lux reading from the IC.
Exponent (E[3:0]): Exponent bits of the lux reading (0000 to 1110). Note: A reading of 1111 represents an overrange
condition.
Mantissa (M[7:4]): Four most significant bits of mantissa byte of the lux reading (0000 to 1111).
Lux = 2(exponent) x mantissa x 0.72
Exponent = 8xE3 + 4xE2 + 2xE1 + E0
Mantissa = 8xM7 + 4xM6 + 2xM5 + M4
A code of 0000 0001 calculates to be 0.72 lux.
A code of 1110 1111 calculates to be 176,947 lux.
A code of 1110 1110 calculates to be 165,151 lux.
Update of the contents of this register is internally disabled during I2C read operations to ensure proper data transfer
between internal ADC and I2C registers. Update of I2C registers is resumed when the master sends a STOP command.
If user wants to read both the Lux High-Byte register 0x03 and Lux Low-Byte register 0x04, then the master should
not send a STOP command between the reads of the two registers. Instead a REPEATED START command should
be used. This ensures accurate data is obtained from the I2C registers (by disabling internal updates during the read
process).
9
MAX9635
Integration Timer Bits (TIM[2:0])
The TIM[2:0] bits can be used to program the signal integration time.
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
Lux Low-Byte Register 0x04
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
—
—
—
—
M3
M2
M1
M0
0x04
Bits in Lux Low-Byte register 0x04 give the 4 least significant bits of the mantissa byte representing the lux reading
of ambient light. Combined with the Lux High-Byte register 0x03, it extends the resolution and dynamic range of lux
measurements of the IC.
E3–E0: Exponent bits of lux reading
M7–M0: Mantissa byte of lux reading
Lux = 2(exponent) x mantissa x 0.045
Exponent = 8xE3 + 4xE2 + 2xE1 + E0
Mantissa = 128xM7 + 64xM6 + 32xM5 + 16xM4 + 8xM3 + 4xM2 + 2xM1 + M0
Combining contents of register 0x03 and 0x04:
A code of 0000 0000 0001 calculates to be 0.045 lux.
A code of 0000 0001 0000 calculates to be 0.72 lux.
A code of 0001 0001 0001 calculates to be 0.765 lux.
A code of 1110 1111 1111 calculates to be 188,006 lux.
A code of 1110 1111 1110 calculates to be 187, 269 lux.
The Lux High-Byte 0x03 and Lux Low-Byte 0x04 register updates are internally disabled at the start of a valid address
transmission from the master. Updating reinitiates at the next valid STOP condition. This prevents erroneous readings,
in the event an update occurs between readings of registers 0x03 and 0x04.
Update of the contents of this register is internally disabled during I2C read operations to ensure proper data transfer
between internal ADC and I2C registers. Update of I2C registers is resumed when the master sends a STOP command.
If the user wants to read both the Lux High-Byte register 0x03 and Lux Low-Byte register 0x04, then the master should
not send a STOP command between the reads of the two registers. Instead a REAPEATED START command should
be used. This ensures accurate data is obtained from the I2C registers (by disabling internal updates during the read
process).
Upper Threshold High-Byte Register 0x05
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
UE3
UE2
UE1
UE0
UM7
UM6
UM5
UM4
0x05
The Upper Threshold register exponent with the four most significant bits of the mantissa sets the upper trip level for
interrupt functionality. This upper limit is relevant only if the INTE bit in the Interrupt Enable register is set. If the lux level
is greater than this light level for a time greater than that specified in the Threshold Timer register, the INTS bit in the
Interrupt Status register is set and the INT pin is pulled low.
Mantissa (UM[7:4]): Four most significant bits of mantissa upper threshold
Exponent (UE[3:0]): Exponent bits upper threshold
Upper lux threshold = 2(exponent) x mantissa x 0.045
Exponent = 8xUE3 + 4xUE2 + 2xUE1 + UE0
Mantissa = 128xUM7 + 64xUM6 + 32xUM5 + 16xUM4 + 15
10
Industry’s Lowest-Power
Ambient Light Sensor with ADC
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
LE3
LE2
LE1
LE0
LM7
LM6
LM5
LM4
0x06
The Lower Threshold register exponent with the four most significant bits of the mantissa sets the lower trip level for
interrupt functionality. This lower limit is relevant only if the INTE bit in the Interrupt Enable register is set. If the lux level
is below this light level for a time greater than that specified in the Threshold Timer register, the INTS bit in the Interrupt
Status register is set and the INT pin is pulled low.
Mantissa (LM[7:4]): Four most significant bits of mantissa lower threshold
Exponent (LE[3:0]): Exponent bits lower threshold
Lower lux threshold = 2(exponent) x mantissa x 0.045
Exponent = 8xLE3 + 4xLE2 + 2xLE1 + LE0
Mantissa = 128xLM7 + 64xLM6 + 32xLM5 + 16xLM4
Threshold Timer Register 0x07
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
REGISTER
ADDRESS
T7
T6
T5
T4
T3
T2
T1
T0
0x07
If the INTE bit = 1 and the ambient light level exceeds either threshold limit for a time longer than that specified by the
Threshold Timer register, then the INTS bit is set to 1 and the INT pin is pulled low.
The value in this register sets the time used to control this delay. A value of 0x00 in this register (with INTE bit = 1 in the
Interrupt Enable register) configures the IC to assert the interrupt pin as soon as the light level exceeds either threshold.
Time delay = (128xT7 + 64xT6 + 32xT5 + 16xT4 + 8xT3 + 4xT2 + 2xT1 + T0) x 100ms.
Applications Information
Auto and Manual Modes
In auto mode configuration (default setting), CDR and
TIM bits are internally generated. The autoranging circuit
uses two different methods to change its sensitivity. For
light intensities greater than 700 lux, a current divider
reduces the photodiode’s current by a factor of 8. The
default, as in the previous example, is a division of 1:
current goes directly into the I to F converter. As light
intensity decreases, the autoranging circuit increases
the integration time from 100ms to 200ms to 400ms, or
to 800ms. The combination of the current divider and the
different integration times give the A/D a range 8 times
higher, as well as 8 times lower, than its nominal 16-bit
range. This gives a dynamic range of 22 bits or slightly
over 4,000,000 to 1.
In manual mode, the user has access to 4 bits (CDR and
TIM[2:0]) to override the autoranging circuitry. These
affect the integration time of the A/D and the current
division ratio. See the register description for manual
configuration mode (0x02, bit 6).
Data Format of Lux Reading
The IC has a user-friendly digital output format. It consists of a 4-bit exponent followed by an 8-bit mantissa.
In its highest sensitivity mode, 1 count represents 0.045
lux. The mantissa has a maximum value of 255, and the
exponent has a maximum value of 14. This gives a maximum range: 255 x 214 = 4,177,920. At 0.045 lux/LSB, the
maximum lux reading is 188,000 lux. Any reading greater
than that (i.e., exponent = 15) is considered to be an
overload. No conversion formulas are needed as in the
case of dual-diode ambient light sensors.
The IC’s output (registers 0x03 and 0x04) comprises a
12-bit result that represents the ambient light expressed
in units of lux.
Here is how lux is calculated:
Lux = (2(exponent) x mantissa) x 0.045
The exponent is a 4-bit number ranging from 0000 to
1110 (zero to 14).
The mantissa is an 8-bit number ranging from 0000 0000
to 1111 1111 (zero to 255).
11
MAX9635
Lower Threshold High-Byte Register 0x06
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
The count is multiplied by 0.045, which is the LSB.
The mantissa is an 8-bit number ranging from 0000 0000
to 1111 0000 (zero to 240).
Because of the logarithmic nature of autoranging circuitry implemented on the IC, resolution of ambient lux
readings scale with the absolute measurement. Table 8
lists the lux resolution and the lux ranges obtained from
the IC.
Upper lux threshold = (2(exponent) x mantissa) x 0.045
The exponent is a 4-bit number ranging from 0000 to
1110 (zero to 14).
The mantissa is an 8-bit number ranging from 0000 1111
to 1111 1111 (15 to 255).
Interrupt Settings
In the auto range mode (MANUAL = 0), the upper threshold and lower threshold bytes must be in a format that
matches the format used in register 0x03, the lux high
byte. There are only two rules to follow:
Interrupt is enabled by setting bit 0 of register 0x01 to
1 (see Table 1). INT, an open-drain output, pulls low
when an interrupt condition occurs (lux readings that
exceed threshold limits for a period greater than that set
by the Time register). The interrupt status bit is cleared
automatically if register 0x00 is read or if the interrupt is
disabled (INTE = 0).
• For very low lux levels (light levels below 11.5 lux),
set the exponent to zero, the code is merely: 0000
MMMM where the 4 zeroes are the exponent, and the
MMMM represent the 4 most significant bits of the
mantissa.
Threshold Register Data Format
The IC’s interrupt circuit requires the upper and lower
limit thresholds to be in a specific format to be properly
interpreted. The upper and lower limits, from registers
0x05 and 0x06 must match the lux high-byte format. This
consists of the 4 bits of the exponent and the 4 most significant bits of the mantissa (E3 E2 E1 E0 M7 M6 M5 M4).
• For all other conditions (light levels above 11.5 lux)
where the exponent is not zero, the format is: EEEE
1MMM. Notice that bit M7 (most significant bit) must
always be a 1. The other bits do not matter. EEEE is
limited to a maximum value of 1110. The maximum
usable setting is a code of 1110 1111.
In this case, there is the following formula:
Lower lux threshold = (2(exponent) x mantissa) x 0.045
The exponent is a 4-bit number ranging from 0000 to
1110 (zero to 14).
In manual mode (MANUAL = 1), Table 9 gives the range
of exponent (E3 E2 E1 E0) that can be used for each
TIM[2:0] and CDR bit setting.
Table 8. Lux per LSB in Automatic Mode
12
LUX (MIN)
LUX (MAX)
LUX PER LSB IN
AUTOMATIC MODE
COUNTS (MIN)
COUNTS (MAX)
0
11.5
0.045
0
256
11.5
23.0
0.09
256
512
23.0
46.1
0.18
512
1024
46.1
92.2
0.36
1024
2048
92.2
184.3
0.72
2048
4096
184.3
368.6
1.44
4096
8192
368.6
737.3
2.88
8192
16,384
737.3
1474.6
5.76
16,384
32,768
1474.6
2949.1
11.52
32,768
65,536
2949.1
5898.2
23.04
65,536
131,072
5898.2
11,796.5
46.08
131,072
262,144
11,796.5
23,593.0
92.16
262,144
524,288
23,593.0
47,185.9
184.32
524,288
1,048,576
47,185.9
94,371.8
368.64
1,048,576
2,097,152
94,371.8
188,006.4
737.28
2,097,152
4,177,920
Industry’s Lowest-Power
Ambient Light Sensor with ADC
RECOMMENDED SETTINGS
FOR CONFIGURATION
REGISTER (0x02)
APPLICATION CONDITIONS
RANGE OF EXPONENTS FOR
UPPER AND LOWER
THRESHOLD REGISTERS
(0x05 AND 0x06)
LUX LSB
(MIN)
LUX
(MAX)
LUX LSB
(MAX)
INTEGRATION
TIME (ms)
TIM[2:0]
CDR
EXPONENT
(MIN)
EXPONENT
(MAX)
0.045
2938
11.52
800
000
0
0000
1000
0.09
5875
23.04
400
001
0
0001
1001
0.18
11,750
46.08
200
010
0
0010
1010
100
011
0
800
000
1
0011
1011
0100
1100
0101
1101
0110
1110
0111
1110
0.36
23,501
92.16
0.72
47,002
184.32
1.44
94,003
368.64
2.88
188,006
737.28
5.76
188,006
737.28
11.52
188,006
23.04
188,006
46.08
188,006
MAX9635
Table 9. Recommended Manual Mode Settings for Configuration Register (0x02) and
Threshold Registers (0x05, 0x06)
50
100
0
400
001
1
25
101
0
200
010
1
12.5
110
0
100
011
1
6.25
111
0
50
100
1
737.28
25
101
1
1000
1110
737.28
12.5
110
1
1001
1110
737.28
6.25
111
1
1010
1110
Note: In manual mode, exceeding the lux (max) causes an overload error (exponent = 1111).
Typical Operating Sequence
To utilize the ultra-low power consumption of the IC in
end applications, an interrupt pin is provided to eliminate
the need for the system to poll the device continuously.
Since every clock and data bit transmitted on I2C can
consume up to 1mA (assuming 1.8kI pullup resistor to
a 1.8V rail), minimizing the number of I2C transactions
on the data bus can save a lot of power. In addition,
eliminating the need to poll the device frees up processing resources for the master, improving overall system
performance.
The typical sequence of communication with the IC is
as follows:
1) Master reads lux reading from registers 0x03 and
0x04.
2) Master sets the upper lux threshold and lower lux
threshold in registers 0x05 and 0x06 so that a userprogrammed window is defined around the current
lux readings.
3) Master sets suitable threshold timer data in register
0x07.
4) Master works on other tasks until alerted by the INT
pin going low. This is where the master spends much
of its time.
5) When alerted by the INT pin going low, the master
reads the Interrupt Status register 0x00 to confirm
the source of interrupt was the IC. The master takes
appropriate action.
6) Repeat from Step 1.
13
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
START
READ MAX9635 AMBIENT LUX,
SET APPROPRIATE BACKLIGHT STRENGTH
WRITE TO UPPER LUX THRESHOLD,
LOWER LUX THRESHOLD, AND
LUX THRESHOLD TIMER REGISTERS
WORK ON TASKS/SLEEP UNTIL WOKEN BY
HARDWARE INTERRUPT
WOKEN BY
INTERRUPT?
N
Y
CHECK OTHER INTERRUPT
SOURCES
READ INTS BIT TO CONFIRM
Y
Figure 2. Typical Operating Sequence
14
MAX9635 CAUSED
INTERRUPT?
N
Industry’s Lowest-Power
Ambient Light Sensor with ADC
The IC features an I2C/SMBus™-compatible, 2-wire
serial interface consisting of a serial-data line (SDA) and
a serial-clock line (SCL). SDA and SCL facilitate communication between the IC and the master at clock rates
up to 400kHz. Figure 3 shows the 2-wire interface timing
diagram. The master generates SCL and initiates data
transfer on the bus. A master device writes data to the
IC by transmitting the proper slave address followed by
the register address and then the data word. Each transmit sequence is framed by a START (S) or REPEATED
START (Sr) condition and a STOP (P) condition. Each
word transmitted to the IC is 8 bits long and is followed
by an acknowledge clock pulse. A master reading data
from the IC transmits the proper slave address followed
by a series of nine SCL pulses. The IC transmits data on
SDA in sync with the master-generated SCL pulses. The
master acknowledges receipt of each byte of data. Each
read sequence is framed by a START or REPEATED
START condition, a not acknowledge, and a STOP condition. SDA operates as both an input and an open-drain
output. A pullup resistor, typically greater than 500I, is
required on the SDA bus. SCL operates as only an input.
A pullup resistor, typically greater than 500I, is required
on SCL if there are multiple masters on the bus, or if the
master in a single-master system has an open-drain SCL
output. Series resistors in line with SDA and SCL are
optional. Series resistors protect the digital inputs of the
IC from high-voltage spikes on the bus lines, and minimize crosstalk and undershoot of the bus signals.
Bit Transfer
One data bit is transferred during each SCL cycle. The
data on SDA must remain stable during the high period
of the SCL pulse. Changes in SDA while SCL is high are
control signals (see the START and STOP Conditions
section). SDA and SCL idle high when the I2C bus is not
busy.
START and STOP Conditions
SDA and SCL idle high when the bus is not in use. A
master initiates communication by issuing a START condition. A START condition is a high-to-low transition on
SDA with SCL high. A STOP condition is a low-to-high
transition on SDA while SCL is high (Figure 4). A START
condition from the master signals the beginning of a
transmission to the IC. The master terminates transmission, and frees the bus, by issuing a STOP condition. The
bus remains active if a REPEATED START condition is
generated instead of a STOP condition.
Early STOP Conditions
The IC recognizes a STOP condition at any point during
data transmission except if the STOP condition occurs in
the same high pulse as a START condition. For proper
operation, do not send a STOP condition during the
same SCL high pulse as the START condition.
SDA
tSU,STA
tSU,DAT
tHD,DAT
tLOW
tBUF
tHD,STA
tSP
tSU,STO
SCL
tHIGH
tHD,STA
START
CONDITION
tR
tF
REPEATED
START CONDITION
STOP
CONDITION
START
CONDITION
Figure 3. 2-Wire Interface Timing Diagram
SMBus is a trademark of Intel Corp.
15
MAX9635
I2C Serial Interface
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
S
SR
P
CLOCK PULSE FOR
ACKNOWLEDGMENT
START
CONDITION
SCL
SCL
1
2
8
9
NOT ACKNOWLEDGE
SDA
SDA
ACKNOWLEDGE
Figure 4. START, STOP, and REPEATED START Conditions
Figure 5. Acknowledge
Slave Address
The slave address with the R/W bit set to 0 indicates
that the master intends to write data to the IC. The IC
acknowledges receipt of the address byte during the
master-generated ninth SCL pulse.
Acknowledge
The second byte transmitted from the master configures
the IC’s internal register address pointer. The pointer
tells the IC where to write the next byte of data. An
acknowledge pulse is sent by the IC upon receipt of the
address pointer data.
The slave address is controlled by the A0 pin. Connect
A0 to either ground or VCC to set the address. Table 10
shows the two possible addresses for the IC.
The acknowledge bit (ACK) is a clocked 9th bit that the
IC uses to handshake receipt each byte of data when in
write mode (see Figure 5). The IC pulls down SDA during the entire master-generated ninth clock pulse if the
previous byte is successfully received. Monitoring ACK
allows for detection of unsuccessful data transfers. An
unsuccessful data transfer occurs if a receiving device
is busy or if a system fault has occurred. In the event of
an unsuccessful data transfer, the bus master can retry
communication. The master pulls down SDA during the
ninth clock cycle to acknowledge receipt of data when
the IC is in read mode. An acknowledge is sent by the
master after each read byte to allow data transfer to
continue. A not acknowledge is sent when the master
reads the final byte of data from the IC, followed by a
STOP condition.
Write Data Format
A write to the IC includes transmission of a START condition, the slave address with the R/W bit set to 0, one byte
of data to configure the internal register address pointer,
one or more bytes of data, and a STOP condition. Figure
6 illustrates the proper frame format for writing one byte
of data to the IC.
The third byte sent to the IC contains the data that is written to the chosen register. The master signals the end of
transmission by issuing a STOP condition.
Read Data Format
To read a byte of data, the register pointer must first be
set through a write operation (Figure 7). Send the slave
address with the R/W set to 0, followed by the address
of the register that needs to be read. After a repeated
start condition, send the slave address with the R/W bit
set to 1 to initiate a read operation. The IC then sends
an acknowledge pulse followed by the contents of the
register to be read. Transmitted data is valid on the rising
edge of the master-generated serial clock (SCL).
Sensor Position
The photo sensitive area of the IC is 0.37mm x 0.37mm
and much smaller than the device itself. When placing
the part behind a light guide, only this sensitive area has
to be taken into account. Figure 8 shows the position and
size of the photo sensitive area within the package.
Table 10. Slave Address
16
A0
SLAVE ADDRESS
FOR WRITING
SLAVE ADDRESS
FOR READING
GND
0x94
0x95
VCC
0x96
0x97
Chip Information
PROCESS: BiCMOS
Industry’s Lowest-Power
Ambient Light Sensor with ADC
MAX9635
ACKNOWLEDGE FROM MAX9635
B7
ACKNOWLEDGE FROM MAX9635
SLAVE ADDRESS
S
B6
B5
B4
B3
B2
B1
B0
ACKNOWLEDGE FROM MAX9635
0
REGISTER ADDRESS
A
A
DATA BYTE
A
R/W
P
1 BYTE
Figure 6. Writing 1 Byte of Data to the IC
NOT ACKNOWLEDGE FROM MASTER
ACKNOWLEDGE FROM MAX9635
S
SLAVE ADDRESS
0
ACKNOWLEDGE FROM MAX9635
A
REGISTER ADDRESS
ACKNOWLEDGE FROM MAX9635
A
Sr
SLAVE ADDRESS
1
R/W
REPEATED START
R/W
A
DATA BYTE
A
P
1 BYTE
Figure 7. Reading One Indexed Byte of Data from the IC
VCC
0.76mm
2mm
1
MAX9635
6
SDA
5
SCL
4
INT
TOP VIEW
A0
2
3
CENTER OF
MAX9635
0.24mm
0.13mm
0.88mm
0.87mm
GND
2mm
0.75mm
0.12mm
0.25mm
Figure 8. Sensor Position
17
Industry’s Lowest-Power
Ambient Light Sensor with ADC
MAX9635
Typical Application Circuit
VCC TO 3.6V
1.7V TO 3.6V
0V TO VCC
1µF
10kI
10kI
VCC
SDA
SDA
GND
SCL
SCL
A0*
INT
INT
MAX9635
*DEVICE ADDRESS IS 0x94. CONNECT
A0 TO VCC FOR SLAVE ADDRESS 0x96.
SEE THE PIN DESCRIPTION.
18
10kI
SDA
SDA
SCL
SCL
I2C SLAVE_1
I2C SLAVE_n
MICROCONTROLLER
(I2C MASTER)
Industry’s Lowest-Power
Ambient Light Sensor with ADC
PACKAGE TYPE
PACKAGE CODE
OUTLINE NO.
LAND PATTERN NO.
6 OTDFN
D622N+1
21-0490
90-0344
19
MAX9635
Package Information
For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”,
or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9635
Industry’s Lowest-Power
Ambient Light Sensor with ADC
Revision History
REVISION
NUMBER
REVISION
DATE
0
8/10
Initial release
—
1
2/11
Updated test time and repeatability
2
2
5/11
Updated Note 2
3
DESCRIPTION
PAGES
CHANGED
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time.
20
© 2011
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
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