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19-5492; Rev 0; 11/10
TION KIT EVALUA BLE AVAILA
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
General Description Features
S Wide 0.025 Lux to 104,444 Lux Range S Small, 2mm x 2mm x 0.6mm UTDFN-Opto S VCC = 1.7V to 3.6V S ICC = 0.65A Operating Current S -40NC to +85NC Temperature Range S Improved Sensitivity Behind Dark Glass
The MAX44007 ambient light sensor features an I2C digital output that is ideal for a number of portable applications such as smartphones, notebooks, and industrial sensors. At less than 1A operating current, it is the lowest power ambient light sensor in the industry and features an ultra-wide 22-bit dynamic range from 0.025 lux to 104,444 lux. 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 includes two I2C slave address options: 1011 010x and 1011 011x. The IC is designed to operate from a 1.7V to 3.6V supply voltage range and consumes only 0.65A in full operation. It is available in a small, 2mm x 2mm x 0.6mm UTDFN-Opto package.
Ordering Information
PART MAX44007EDT+ *EP = Exposed pad. PIN-PACKAGE 6 UTDFN-Opto-EP* TEMP RANGE -40NC to +85NC
+Denotes a lead(Pb)-free/RoHS-compliant package.
Block Diagram
VCC SDA I2C DIGITAL SIGNAL PROCESSING SCL AO INT
Applications
Tablet PCs/Notebook Computers TVs/Projectors/Displays Digital Lighting Management Portable Devices Cellular Phones/Smartphones Security Systems
MAX44007
IR PHOTODIODE VISIBLE +IR PHOTODIODE 16-BIT ADC 6-BIT RANGE CDR, TIM CONTROL 16-BIT ADC
N
GND
_______________________________________________________________ Maxim Integrated Products 1
For information on other Maxim products, visit Maxim's website at www.maxim-ic.com.
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
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 UTDFN-Opto (derate 11.9mW/NC above +70NC) .....953mW Operating Temperature Range .......................... -40NC to +85NC Soldering Temperature (reflow) ......................................+260NC
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 OPTICAL CHARACTERISTICS Maximum Lux Sensitivity Saturation Ambient Lux Level Total Error Light Source Matching Infrared Transmittance at 850nm Ultraviolet Transmittance at 363nm Dark Level Count Maximum Signal Integration Time Minimum Signal Integration Time ADC Conversion Time POWER SUPPLY Power-Supply Voltage Power-Supply Current DIGITAL I/O CHARACTERISTICS Output Low Voltage SDA, INT INT Leakage Current SCL, SDA, A0 Input Current I2C Input Low Voltage I2C Input High Voltage Address Input Low Voltage Address Input High Voltage Input Capacitance 2 VOL IIH, IIL VIL_I2C VIH_I2C VIL_A0 VIH_A0 ISINK = 6mA TA = +25NC TA = +25NC SDA, SCL SDA, SCL A0 A0 VCC 0.3V 3 0.7 x VCC 0.3 0.06 0.01 0.01 0.4 20 20 0.3 x VCC V nA nA V V V V pF VCC ICC Guaranteed by TE test TA = +25NC, 100 lux, I2C inputs inactive TA = -40NC to +85NC 1.7 0.65 3.6 1.2 1.6 V FA ACT IRR UVR 0LUX TE Fluorescent light Sunlight Green LED 538nm response, TA = +25NC (Note 2) Fluorescent/incandescent light under dark glass TA = +25NC (Note 3) TA = +25NC (Note 3) 0 lux, TA = +25NC, 800ms range Has 50/60Hz rejection Automatic mode, has 50/60Hz rejection Manual mode only 100ms range, TA = +25NC 100ms range 99.6 97 10 2 1.2 0 800 100 6.25 100 103 100.4 107 3 3 0.025 0.025 104,444 15 Lux/LSB Lux % % % % Lux ms ms ms SYMBOL CONDITIONS MIN TYP MAx UNITS
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 1.8V, TMIN to TMAX = -40NC to +85NC, unless otherwise noted.) (Note 1) PARAMETER I2C TIMING fSCL tBUF tHD,STA tLOW tHIGH tSU,STA tHD,DAT tSU,DAT tF tSU,STO tSP Input filters on the SDA and SCL inputs suppress noise spikes ISINK P 6mA, tR and tF are measured between 0.3 x VDD and 0.7 x VDD 0.6 0 50 (Note 4) 1.3 0.6 1.3 0.6 0.6 0 100 100 0.9 400 kHz Fs Fs Fs Fs Fs Fs ns ns Fs ns Serial-Clock Frequency Bus Free Time Between a STOP and a START Condition Hold Time (Repeated) START Condition Low Period of the SCL Clock High Period of the SCL Clock Setup Time for a Repeated START Condition Data Hold Time Data Setup Time Fall Time of SDA Transmitting Setup Time for STOP Condition Pulse Width of Spike Suppressed Note Note Note Note 1: 2: 3: 4: SYMBOL CONDITIONS MIN TYP MAx UNITS
MAX44007
3
All devices are 100% production tested at TA = +25NC. Temperature limits are guaranteed by design. Green 538nm LED chosen for production is such that the IC responds to 100 lux fluorescent light with 100 lux. With respect to green LED 538nm response. 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.
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Typical Operating Characteristics
(VCC = 1.8V, default power upsetting; unless otherwise noted.)
SPECTRUM RESPONSE
MAX44007 toc01
RADIATION PATTERN
RELATIVE SENSITIVITY (% FROM 0) 90 80 70 60 50 40 30 20 10 0 AUTO MODE, INCANDESCENT LAMP
MAX44007 toc02
120 100 NORMALIZED RESPONSE MAX44007 RESPONSE 80 60 40 20 0 300 400 500 600 700 800 900 CIE
100
1000
-90
-60
-30
0
30
60
90
WAVELENGTH (nm)
LUMINOSITY ANGLE ()
SPECTRUM OF LIGHT SOURCES FOR MEASUREMENT
MAX44007 toc03
SUPPLY CURRENT vs. SUPPLY VOLTAGE
0 LUX AND 100 LUX, CONT = 1 1.2 SUPPLY CURRENT (A) 1.0 0.8 0.6 0.4 0.2 AUTO MODE, FLUORESCENT LAMP 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 100 LUX, CONT = 0 5000 LUX, CONT = 0
MAX44007 toc04
160 140 NORMALIZED RESPONSE 120 100 80 60 40 20 0 300 400 500 600 700 800 WAVELENGTH (nm) FLUORESCENT SUNLIGHT INCANDESCENT
1.4
0
900 1000
SUPPLY VOLTAGE (V)
OUTPUT CODE ERROR vs. SUPPLY VOLTAGE
OUTPUT CODE ERROR (RATIO FROM 1.8V) 1.08 1.06 1.04 1.02 1.00 0.98 0.96 0.94 0.92 0.90 1.5 1.8 50 AND 300 LUX AUTO MODE, FLUORESCENT LAMP 2.1 2.4 2.7 3.0 3.3 3.6
MAX44007 toc05
SUPPLY CURRENT vs. TEMPERATURE
VCC = 3.3V
MAX44007 toc06
1.10
1.2 1.0 SUPPLY CURRENT (A) 0.8 0.6 VCC = 2.5V 0.4 0.2 0 -40 -15 10 35 60 100 LUX AUTO MODE, FLUORESCENT LAMP VCC = 1.8V
85
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
4
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
Typical Operating Characteristics (continued)
(VCC = 1.8V, default power upsetting; unless otherwise noted.)
SUPPLY CURRENT vs. LUX READING
MAX44007 toc07
MAX44007
MAX44007 READING vs. LUX LEVEL
MAX44007 toc08
SDA INT OUTPUT LOW VOLTAGE vs. SINK CURRENT
120 110 100 90 80 70 60 50 40 30 20 10 0 0 1 2 3
MAX44007 toc09
3.5 3.0 SUPPLY CURRENT (A) 2.5 2.0 1.5 1.0 0.5 SUNLIGHT 0 100 1k 10k
350 300 200 150 100 50 0 INCANDESCENT LAMP
MAX44007 READING (counts)
SDA
FLUORESCENT LAMP
VOL (mV)
INT
100k
0
100
200
300
400
500
LUX READING (LUX)
REFERENCE METER READING (lux)
456 ISINK (mA)
7
8
9
10
Pin Configuration
TOP VIEW
SDA 6 SCL 5 INT 4
MAX44007
+
EP
1 VCC
2 GND
3 A0
UTDFN-Opto (2mm x 2mm)
Pin Description
PIN 1 2 3 4 5 6 -- NAME VCC GND A0 INT SCL SDA EP Power Supply Ground Address Select. Pull high to select address 1011 011x or low to select address 1011 010x. Interrupt Output. Use an external pullup resistor. I2C Clock Bus I2C Data Bus Exposed Pad. Connect EP to ground. 5 PIN DESCRIPTION
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Detailed Description
The MAX44007 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 (UTDFN-Opto) 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. 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 0.65A) and an extremely wide dynamic light range that extends from 0.025 lux to 104,444 lux--more than a 4,000,000 to 1 range. The onchip autoranging scheme requires no user intervention for the gain-range setting. As darkened glass or translucent materials can be transparent to IR wavelengths while attenuating visible light by 20-50 times or more, the IC dual-photodiode architecture can be utilized to compensate for the increased IR component of incoming light. By allowing the user to adjust the internal gain settings to compensate for the dark glass' profile, the IC excels in challenging low-light level applications. contact the factory for more details. 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 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.
Human Eye CIE Curve and Different Light Sources
120 100 NORMALIZED RESPONSE MAX44007 RESPONSE 80 60 40 20 0 300 400 500 600 700 800 900 1000 WAVELENGTH (nm) CIE
Figure 1. Spectral Sensitivity of the MAX44007 and Human Eye
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Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
Register and Bit Descriptions
Table 1. Register Map
REGISTER 7 STATUS Interrupt Status Interrupt Enable CONFIGURATION Configuration LUx READING Lux High Byte Lux Low Byte THRESHOLD SET Upper Threshold High Byte Lower Threshold High Byte Threshold Timer THRESHOLD SET Adv1 Register Adv2 Register Visible Gain Register IR Gain Register Trim Enable Register X X X X 1 X X X X 0 X X X X 0 X X X X 0 X X X X 0 X X X X 0 X X X X 0 X X X X ADV 0x09 0xA 0xB 0xC OxD 0xXX 0xXX 0xXX 0xXX 0x80 R/SW R/SW R/SW R/SW R/W UE3 LE3 T7 UE2 LE2 T6 UE1 LE1 T5 UE0 LE0 T4 UM7 LM7 T3 UM6 LM6 T2 UM5 LM5 T1 UM4 LM4 T0 0x05 0x06 0x07 0xFF 0x00 0xFF R/W R/W R/W E3 -- E2 -- E1 -- E0 -- M7 M3 M6 M2 M5 M1 M4 M0 0x03 0x04 0x00 0x00 R R CONT MANUAL -- -- CDR TIM[2:0] 0x02 0x03 R/W -- -- -- -- -- -- -- -- -- -- -- -- -- -- INTS INTE 0x00 0x01 0x00 0x00 R R/W 6 5 BIT 4 3 2 1 0 REGISTER ADDRESS POWER-ON RESET STATE R/W
MAX44007
7
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Interrupt Status 0x00
BIT 7 -- BIT 6 -- BIT 5 -- BIT 4 -- BIT 3 -- BIT 2 -- BIT 1 -- BIT 0 INTE REGISTER ADDRESS 0x00
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 0 1 No interrupt trigger event has occurred. Ambient light intensity is outside the threshold window range for a longer than specified time. OPERATION
Interrupt Enable 0x01
BIT 7 -- BIT 6 -- BIT 5 -- BIT 4 -- BIT 3 -- BIT 2 -- BIT 1 -- BIT 0 INTE REGISTER ADDRESS 0x00
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 0 1 OPERATION The INT pin and the INTS bit are not asserted even if an interrupt event has occurred. 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 CONT BIT 6 MANUAL BIT 5 -- BIT 4 -- BIT 3 CDR BIT 2 BIT 1 TIM[2:0] BIT 0 REGISTER ADDRESS 0x02
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Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
Continuous Mode
MAX44007
Table 4. Continuous Mode Register
BIT 7 0 OPERATION 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. 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.
1
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 0 1 OPERATION Default mode of configuration is used for the IC. In this mode, CDR, TIM[2:0] bits are automatically determined by the internal autoranging circuitry of the IC. 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 0 1 OPERATION Current not divided. All of the photodiode current goes to the ADC. Current divided by 8. Only 1/8 of the photodiode current goes to the ADC. This mode is used in high-brightness situations.
9
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Integration Timer Bits (TIM[2:0]) The TIM[2:0] bits can be used to program the signal integration time. 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, 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] 000 001 010 011 100 101 110 111 INTREGRATION TIME (ms) 800 400 200 100 50 25 12.5 6.25 -- -- This is a preferred mode for high-brightness applications. Manual mode only. Manual mode only. Manual mode only. Manual mode only. COMMENTS This is a preferred mode for boosting low-light sensitivity.
Lux High-Byte Register 0x03
BIT 7 E3 BIT 6 E2 BIT 5 E1 BIT 4 E0 BIT 3 M7 BIT 2 M6 BIT 1 M5 BIT 0 M4 REGISTER ADDRESS 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 0.04 Exponent = 8xE3 + 4xE2 + 2xE1 + E0 Mantissa = 8xM7 + 4xM6 + 2xM5 + M4 A code of 0000 0001 calculates to be 0.04 lux. A code of 1110 1111 calculates to be 98,304 lux. A code of 1110 1110 calculates to be 91,751 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).
10
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
Lux Low-Byte Register 0x04
BIT 7 -- BIT 6 -- BIT 5 -- BIT 4 -- BIT 3 M3 BIT 2 M2 BIT 1 M1 BIT 0 M0 REGISTER ADDRESS 0x04
MAX44007
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 0.025 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 0.025 lux. A code of 0000 0001 0000 calculates to be 0.04 lux. A code of 0001 0001 0001 calculates to be 0.425 lux. A code of 1110 1111 1111 calculates to be 104,448 lux. A code of 1110 1111 1110 calculates to be 104,038 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 UE3 BIT 6 UE2 BIT 5 UE1 BIT 4 UE0 BIT 3 UM7 BIT 2 UM6 BIT 1 UM5 BIT 0 UM4 REGISTER ADDRESS 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 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 0.025 Exponent = 8xUE3 + 4xUE2 + 2xUE1 + UE0 Mantissa = 128xUM7+ 64xUM6+ 32xUM5 + 16xUM4 +15
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Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Lower Threshold High-Byte Register 0x06
BIT 7 LE3 BIT 6 LE2 BIT 5 LE1 BIT 4 LE0 BIT 3 LM7 BIT 2 LM6 BIT 1 LM5 BIT 0 LM4 REGISTER ADDRESS 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 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 0.025 Exponent = 8xLE3 + 4xLE2 + 2xLE1 + LE0 Mantissa = 128xLM7 + 64xLM6 + 32xLM5 + 16xLM4
Threshold Timer Register 0x07
BIT 7 T7 BIT 6 T6 BIT 5 T5 BIT 4 T4 BIT 3 T3 BIT 2 T2 BIT 1 T1 BIT 0 T0 REGISTER ADDRESS 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 Configuration 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
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).
Auto and Manual Modes
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 0.025 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 0.025 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 0.025 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).
Data Format of Lux Reading
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Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
The count is multiplied by 0.045, which is the LSB. 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. 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). 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). In this case, there is the following formula: Lower lux threshold = (2(exponent) x mantissa) x 0.025 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 0000 (zero to 240). Upper lux threshold = (2(exponent) x mantissa) x 0.025 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). 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: * For very low lux levels (light levels below 6.4 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. * For all other conditions (light levels above 6.4 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 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.
MAX44007
Interrupt Settings
Threshold Register Data Format
Table 8. Lux per LSB in Automatic Mode
LUx (MIN) 0 6.4 12.8 25.6 51.2 102.4 204.8 409.6 819.2 1638.4 3276.8 6553.6 13,107.2 26,214.4 52,428.8 LUx (MAx) 6.4 12.8 25.6 51.2 102.4 204.8 409.6 819.2 1638.4 3276.8 6553.6 13,107.2 26,214.9 54,428.8 104,448.0 LUx PER LSB IN AUTOMATIC MODE 0.025 0.05 0.1 0.2 0.4 0.8 1.6 3.2 6.4 12.8 25.6 51.2 102.4 204.8 409.6 COUNTS (MIN) 0 256 512 1024 2048 4096 8192 16,384 32,768 65,536 131,072 262,144 524,288 1,048,576 2,097,152 COUNTS (MAx) 256 512 1024 2048 4096 8192 16,384 32,768 65,536 131,072 262,144 524,288 1,048,576 2,097,152 4,177,920
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Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Table 9. Recommended Manual Mode Settings for Configuration Register (0x02) and Threshold Registers (0x05, 0x06)
APPLICATION CONDITIONS LUx LSB (MIN) 0.025 0.05 0.1 0.2 0.4 0.8 1.6 3.2 6.4 12.8 25.6 LUx (MAx) 1632 3264 6528 13,056 26,112 52,224 104,448 104,448 104,448 104,448 104,448 LUx LSB (MAx) 6.4 12.8 25.6 51.2 102.4 204.8 409.6 409.6 409.6 409.6 409.6 INTEGRATION TIME (ms) 800 400 200 100 800 50 400 25 200 12.5 100 6.25 50 25 12.5 6.25 RECOMMENDED SETTINGS FOR CONFIGURATION REGISTER (0x03) TIM 000 001 010 011 000 100 001 101 010 110 011 111 100 101 110 111 CDR 0 0 0 0 1 0 1 0 1 0 1 0 1 1 1 1 RANGE OF ExPONENTS FOR UPPER AND LOWER REGISTERS (0x05 AND 0x06) ExPONENT (MIN) 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 ExPONENT (MAx) 1000 1001 1010 1011 1100 1101 1110 1110 1110 1110 1110
Note: In manual mode, exceeding the lux (max) causes an overload error (exponent = 1111).
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.
Typical Operating Sequence
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.
14
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
START
READ MAX44007 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
READ INTS BIT TO CONFIRM
CHECK OTHER INTERRUPT SOURCES
Y
MAX44007 CAUSED INTERRUPT?
N
Figure 2. Typical Operating Sequence
15
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
I2C Serial Interface
The IC features an I2C/SMBusTM-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. 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. 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. 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.
Bit Transfer
START and STOP Conditions
Early STOP Conditions
SDA tSU,DAT tLOW SCL tHIGH tHD,STA START CONDITION tR tF REPEATED START CONDITION STOP CONDITION START CONDITION tHD,DAT tSU,STA tBUF tHD,STA tSP tSU,STO
Figure 3. 2-Wire Interface Timing Diagram
SMBus is a trademark of Intel Corp.
16
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
S SR P START CONDITION SCL
1 2
CLOCK PULSE FOR ACKNOWLEDGMENT
SCL
8
9
NOT ACKNOWLEDGE SDA SDA ACKNOWLEDGE
Figure 4. START, STOP, and REPEATED START Conditions
Figure 5. Acknowledge
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. 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.
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. 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 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. 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). 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.
Acknowledge
Read Data Format
Write Data Format
Sensor Position
Table 10. Slave Address
A0 GND VCC SLAVE ADDRESS FOR WRITING 1011 0100 1011 0110 SLAVE ADDRESS FOR READING 1011 0101 1011 0111
17
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
ACKNOWLEDGE FROM MAX44007 B7 ACKNOWLEDGE FROM MAX44007 S SLAVE ADDRESS R/W 0 A ACKNOWLEDGE FROM MAX44007 REGISTER ADDRESS A DATA BYTE 1 BYTE A P B6 B5 B4 B3 B2 B1 B0
Figure 6. Writing 1 Byte of Data to the IC
NOT ACKNOWLEDGE FROM MASTER ACKNOWLEDGE FROM MAX44007 S SLAVE ADDRESS R/W 0 A ACKNOWLEDGE FROM MAX44007 REGISTER ADDRESS A ACKNOWLEDGE FROM MAX44007 Sr SLAVE ADDRESS R/W 1 A DATA BYTE 1 BYTE A P
REPEATED START
Figure 7. Reading One Indexed Byte of Data from the IC
2mm
0.76mm
VCC
1
MAX44007
TOP VIEW
0.24mm 0.13mm 0.88mm
6
SDA
0.75mm GND 2 5 SCL 2mm
CENTER OF MAX44007
0.87mm
0.12mm 0.25mm 4 INT
AD
3
Figure 8. Sensor Position
18
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
Typical Application Circuit
MAX44007
1.7V TO 3.6V
VCC TO 3.6V 0V TO VCC 1F 10kI 10kI 10kI
VCC GND A0*
SDA SCL INT
SDA SCL INT
MAX44007
*DEVICE ADDRESS IS 1011 010x. CONNECT A0 TO VCC FOR SLAVE ADDRESS 1011 011x. SEE THE PIN DESCRIPTION.
SDA SCL I2C SLAVE_1
SDA SCL I2C SLAVE_n
MICROCONTROLLER (I2CMASTER)
Chip Information
PROCESS: BiCMOS
19
Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity MAX44007
Package Information
For the latest package outline information and land patterns, 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.
PACKAGE TYPE 6 UTDFN-Opto PACKAGE CODE D622+1 OUTLINE NO. 21-0490 LAND PATTERN NO. 90-0344
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Low-Power Digital Ambient Light Sensor with Enhanced Sensitivity
Revision History
REVISION NUMBER 0 REVISION DATE 11/10 Initial release DESCRIPTION PAGES CHANGED --
MAX44007
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
(c)
21
2010 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.

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