MAX9635EDT+T - Maxim Integrated

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Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

19-5284; Rev 2; 5/11

General Description

The MAX9635 ambient light sensor features an I2C digi-

tal output that is ideal for a number of portable applica-

tions 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.

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 sup-

ply voltage range and consumes only 0.65µA in full

operation. It is available in a small, 2mm x 2mm x 0.6mm

OTDFN package.

Applications

Tablet PCs/Notebook Computers

TVs/Projectors/Displays

Digital Lighting Management

Portable Devices

Cellular Phones/Smartphones

Security Systems

Features

S Wide 0.045 Lux to 188,000 Lux Range

S Small, 2mm x 2mm x 0.6mm OTDFN

S VCC = 1.7V to 3.6V

S ICC = 0.65µA Operating Current

S -40 NC to +85NC Temperature Range

Ordering Information

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

Block Diagram

EVALUATION KIT

AVAILABLE

PART PIN-PACKAGE TEMP RANGE

MAX9635EDT+ 6 OTDFN-EP* -40NC to +85NC

DIGITAL

SIGNAL

PROCESSING

6-BIT RANGE

CDR, TIM

CONTROL

VISIBLE +IR

PHOTODIODE

I2C

VCC

MAX9635

GND

SCL

SDA

INT

16-BIT

ADC

16-BIT

ADC

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

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.

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

ELECTRICAL CHARACTERISTICS

(VCC = 1.8V, TMIN to TMAX = -40NC to +85NC, unless otherwise noted.) (Note 1)

ABSOLUTE MAXIMUM RATINGS

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

OPTICAL CHARACTERISTICS

Maximum Lux Sensitivity Fluorescent light 0.045 Lux/LSB

Saturation Ambient Lux Level Sunlight 188,000 Lux

Total Error TE Green LED 538nm response,

TA = +25NC (Note 2) 15 %

Light Source Matching Fluorescent/incandescent light 10 %

Infrared Transmittance at 940nm IRR TA = +25NC (Note 3) 0 0.5 %

Ultraviolet Transmittance at

363nm UVR TA = +25NC (Note 3) 1.2 %

Dark Level Count 0LUX 0 lux, TA = +25NC, 800ms range 0 0.045 Lux

Maximum Signal Integration

Time Has 50/60Hz rejection 800 ms

Minimum Signal Integration Time Automatic mode, has 50/60Hz rejection 100 ms

Manual mode only 6.25

ADC Conversion Time ACT 100ms range, TA = +25NC99.6 100 100.4 ms

100ms range 97 103 107

POWER SUPPLY

Power-Supply Voltage VCC Guaranteed by TE test 1.7 3.6 V

Power-Supply Current ICC TA = +25NC, 90 lux, I2C inputs inactive 0.65 1.2 FA

TA = -40NC to +85NC1.6

DIGITAL I/O CHARACTERISTICS

Output Low Voltage SDA, INT VOL ISINK = 6mA 0.06 0.4 V

INT Leakage Current TA = +25NC0.01 20 nA

SCL, SDA, A0 Input Current IIH, IIL TA = +25NC0.01 20 nA

I2C Input Low Voltage VIL_I2C SDA, SCL 0.3 x

VCC V

I2C Input High Voltage VIH_I2C SDA, SCL 0.7 x

VCC V

Address Input Low Voltage VIL_A0 A0 0.3 V

Address Input High Voltage VIH_A0 A0 VCC -

0.3V V

Input Capacitance 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)

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.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

I2C TIMING

Serial-Clock Frequency fSCL 400 kHz

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) 0 0.9 Fs

Data Setup Time tSU,DAT 100 ns

Fall Time of SDA Transmitting tFISINK P 6mA, tR and tF are measured

between 0.3 x VDD and 0.7 x VDD 100 ns

Setup Time for STOP Condition tSU,STO 0.6 Fs

Pulse Width of Spike

Suppressed tSP Input filters on the SDA and SCL inputs

suppress noise spikes 0 50 ns

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Typical Operating Characteristics

(VCC = 1.8V, default power upsetting; unless otherwise noted.)

SPECTRUM RESPONSE

MAX9635 toc01

WAVELENGTH (nm)

CIE

NORMALIZED RESPONSE

900800700600500400

100

120

300 1000

MAX9635 RESPONSE

RADIATION PATTERN

MAX9635 toc02

LUMINOSITY ANGLE (°)

RELATIVE SENSITIVITY (% FROM 0°)

60300-30-60

100

-90 90

AUTO MODE,

INCANDESCENT LAMP

SPECTRUM OF LIGHT SOURCES

FOR MEASUREMENT

MAX9635 toc03

WAVELENGTH (nm)

NORMALIZED RESPONSE

900800400 500 600 700

100

120

140

160

300 1000

INCANDESCENT

SUNLIGHT

FLUORESCENT

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX9635 toc04

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

3.33.02.72.42.11.8

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.5 3.6

0 LUX AND 100 LUX, CONT = 1

5000 LUX, CONT = 0

100 LUX, CONT = 0

AUTO MODE,

FLUORESCENT LAMP

OUTPUT CODE ERROR vs. SUPPLY VOLTAGE

MAX9635 toc05

SUPPLY VOLTAGE (V)

OUTPUT CODE ERROR (RATIO FROM 1.8V)

3.33.02.4 2.72.11.8

0.92

0.94

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

0.90

1.5 3.6

50 AND 300 LUX

AUTO MODE,

FLUORESCENT LAMP

SUPPLY CURRENT vs. TEMPERATURE

MAX9635 toc06

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

603510-15

0.2

0.4

0.6

0.8

1.0

1.2

-40 85

100 LUX

AUTO MODE,

FLUORESCENT LAMP

VCC = 1.8V

VCC = 2.5V

VCC = 3.3V

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Typical Operating Characteristics (continued)

(VCC = 1.8V, default power upsetting; unless otherwise noted.)

Pin Configuration

Pin Description

SUPPLY CURRENT vs. LUX READING

MAX9635 toc07

LUX READING (LUX)

SUPPLY CURRENT (µA)

10k1k

0.5

1.0

1.5

2.0

2.5

3.0

3.5

100 100k

SUNLIGHT

LIGHT SENSITIVITY vs. LUX LEVEL

MAX9635 toc08

REFERENCE METER READING (LUX)

MAX9635 READING (LUX)

25020015010050

100

150

200

250

300

350

0 300

FLUORESCENT

LAMP

INCANDESCENT

LAMP

SDA, INT OUTPUT LOW VOLTAGE

vs. SINK CURRENT

MAX9635 toc09

ISINK (mA)

VOL (mV)

986 72 3 4 51

100

110

120

0 10

INT

SDA

VCC

SDA

GND

SCL

INT

OTDFN

(2mm x 2mm)

TOP VIEW

MAX9635

PIN NAME FUNCTION

1 VCC Power Supply

2 GND Ground

3 A0 Address Select. Pull high to select address 0x96 or low to select address 0x94.

4INT Interrupt Output. Use an external pullup resistor.

5 SCL I2C Clock Bus

6 SDA I2C Data Bus

— EP Exposed Pad. Connect EP to ground.

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Detailed Description

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 photodi-

ode 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 out-

put 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 sig-

nificant power saving.

A package-level optical filter prevents ultraviolet

and infrared from reaching the photodiode. Its opti-

cal 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 on-

chip autoranging scheme requires no user intervention

for the gain-range setting.

The IC can be customized to operate at enhanced sen-

sitivity in applications where it needs to operate behind

a dark glass.

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.

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 bright-

ness 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 environ-

ment 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.

Figure 1. Spectral Sensitivity of the MAX9635 and Human Eye

WAVELENGTH (nm)

CIE

NORMALIZED RESPONSE

900800700600500400

100

120

300 1000

MAX9635 RESPONSE

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Table 1. Register Map

Table 2. Interrupt Status Register

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.

Interrupt Status 0x00

Interrupt Enable 0x01

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 REGISTER

ADDRESS

— — — — — — — INTS 0x01

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 REGISTER

ADDRESS

— — — — — — — INTS 0x01

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.

BIT REGISTER

ADDRESS

POWER-ON

RESET

STATE

R/W

7 6 5 4 3 2 1 0

STATUS

Interrupt Status — — — — — — — INTS 0x00 0x00 R

Interrupt Enable — — — — — — — INTE 0x01 0x00 R/W

CONFIGURATION

Configuration CONT MANUAL — — CDR TIM[2:0] 0x02 0x03 R/W

LUX READING

Lux High Byte E3 E2 E1 E0 M7 M6 M5 M4 0x03 0x00 R

Lux Low Byte — — — — M3 M2 M1 M0 0x04 0x00 R

THRESHOLD SET

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

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Current Division Ratio (CDR)

The CDR bit controls the current division ratio. The photodiode current is divided as shown in Table 6.

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.

Continuous Mode

Configuration 0x02

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

Table 4. Continuous Mode Register

Table 5. Manual Configuration Register

Table 6. Current Division Ratio Register

Note: Continuous mode is independent of the manual configuration mode setting.

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 REGISTER

ADDRESS

CONT MANUAL — — CDR TIM[2:0] 0x02

BIT 0 OPERATION

0The INT pin and the INTS bit are not asserted even if an interrupt event has occurred.

1Detection of an interrupt event triggers a hardware interrupt (INT pin is pulled low) and sets the INTS bit

(register 0x00, bit 0).

BIT 7 OPERATION

0Default 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.

BIT 6 OPERATION

0Default mode of configuration is used for the IC. In this mode, CDR and TIM[2:0] bits are automatically deter-

mined by the internal autoranging circuitry of the IC.

1Manual mode of configuration is used for the IC. In this mode, CDR and TIM[2:0] bits can be programmed

by the user.

BIT 3 OPERATION

0 Current not divided. All of the photodiode current goes to the ADC.

1Current 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

MAX9635

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).

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 (MANUAL = 1), integration time can be varied by the user all the way

from 6.25ms to 800ms. See Table 7.

Lux High-Byte Register 0x03

Table 7. Integration Time

TIM[2:0] INTEGRATION

TIME (ms) COMMENTS

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.

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

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

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

Upper Threshold High-Byte Register 0x05

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).

Lux Low-Byte Register 0x04

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

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 REGISTER

ADDRESS

— — — — M3 M2 M1 M0 0x04

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

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 con-

sists 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 maxi-

mum 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).

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.

Threshold Timer Register 0x07

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

Lower Threshold High-Byte Register 0x06

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

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

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Table 8. Lux per LSB in Automatic Mode

The count is multiplied by 0.045, which is the LSB.

Because of the logarithmic nature of autoranging cir-

cuitry 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 Settings

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).

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 sig-

nificant 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 0.045

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 0000 (zero to 240).

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).

In the auto range mode (MANUAL = 0), the upper thresh-

old 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 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.

• 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 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.

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

MAX9635

Table 9. Recommended Manual Mode Settings for Configuration Register (0x02) and

Threshold Registers (0x05, 0x06)

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 process-

ing 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 user-

programmed 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.

APPLICATION CONDITIONS

RECOMMENDED SETTINGS

FOR CONFIGURATION

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

0.36 23,501 92.16 100 011 0 0011 1011

800 000 1

0.72 47,002 184.32 50 100 0 0100 1100

400 001 1

1.44 94,003 368.64 25 101 0 0101 1101

200 010 1

2.88 188,006 737.28 12.5 110 0 0110 1110

100 011 1

5.76 188,006 737.28 6.25 111 0 0111 1110

50 100 1

11.52 188,006 737.28 25 101 1 1000 1110

23.04 188,006 737.28 12.5 110 1 1001 1110

46.08 188,006 737.28 6.25 111 1 1010 1110

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Figure 2. Typical Operating Sequence

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?

READ INTS BIT TO CONFIRM CHECK OTHER INTERRUPT

SOURCES

MAX9635 CAUSED

INTERRUPT?

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

SMBus is a trademark of Intel Corp.

Figure 3. 2-Wire Interface Timing Diagram

I2C Serial Interface

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 com-

munication 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 trans-

mit 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 condi-

tion. 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 mini-

mize 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 con-

dition. 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 transmis-

sion, 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.

SCL

SDA

START

CONDITION

STOP

CONDITION

REPEATED

START CONDITION

START

CONDITION

tHD,STA

tSU,STA tHD,STA tSP

tBUF

tSU,STO

tLOW

tSU,DAT

tHD,DAT

tHIGH

tRtF

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Figure 4. START, STOP, and REPEATED START Conditions Figure 5. Acknowledge

Table 10. Slave Address

Chip Information

PROCESS: BiCMOS

Slave Address

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.

Acknowledge

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 dur-

ing 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 condi-

tion, 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 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 writ-

ten 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

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.

SCL

SDA

S SR P

SCL

START

CONDITION

SDA

2 8 9

CLOCK PULSE FOR

ACKNOWLEDGMENT

ACKNOWLEDGE

NOT ACKNOWLEDGE

A0 SLAVE ADDRESS

FOR WRITING

SLAVE ADDRESS

FOR READING

GND 0x94 0x95

VCC 0x96 0x97

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Figure 6. Writing 1 Byte of Data to the IC

Figure 7. Reading One Indexed Byte of Data from the IC

Figure 8. Sensor Position

0SLAVE ADDRESS REGISTER ADDRESS DATA BYTE

ACKNOWLEDGE FROM MAX9635

1 BYTE

ACKNOWLEDGE FROM MAX9635

B1 B0B3 B2B5 B4B7 B6

S AA P

R/W

ACKNOWLEDGE FROM MAX9635

1 BYTE

ACKNOWLEDGE FROM MAX9635

NOT ACKNOWLEDGE FROM MASTER

AA P

ACKNOWLEDGE FROM MAX9635

R/W

S A

R/W

REPEATED START

Sr 1

SLAVE ADDRESS REGISTER ADDRESS SLAVE ADDRESS DATA BYTE

TOP VIEW

0.13mm

0.24mm

0.12mm

0.25mm

CENTER OF

MAX9635

VCC SDA

GND SCL

A0 INT

0.88mm

0.75mm

2mm

0.76mm

0.87mm

2mm

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

Typical Application Circuit

1.7V TO 3.6V

1µF

VCC TO 3.6V

0V TO VCC

10kI10kI10kI

SDA

MICRO-

CONTROLLER

(I2C MASTER)

SCL

SDA

I2C SLAVE_n

VCC

GND

A0*

*DEVICE ADDRESS IS 0x94. CONNECT

A0 TO VCC FOR SLAVE ADDRESS 0x96.

SEE THE PIN DESCRIPTION.

INT

SCL

SDA

SCL

INT

MAX9635

SCL

SDA

I2C SLAVE_1

Industry’s Lowest-Power

Ambient Light Sensor with ADC

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.

PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.

6 OTDFN D622N+1 21-0490 90-0344

Industry’s Lowest-Power

Ambient Light Sensor with ADC

MAX9635

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 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 8/10 Initial release —

1 2/11 Updated test time and repeatability 2

2 5/11 Updated Note 2 3