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ISL29023

Integrated Digital Ambient Light Sensor with Interrupt Function

Intersil 

ISL29023

Principles of Operation

Photodiodes and ADC

The ISL29023 contains two photodiode arrays which convert

light into current. The spectral response for ambient light

sensing and IR sensing is shown in Figure 5 in the performance

curves section. After light is converted to current during the light

signal process, the current output is converted to digital by a

built-in 16-bit Analog-to-Digital Converter (ADC). An I2C

command reads the ambient light or IR intensity in counts.

The converter is a charge-balancing integrating type 16-bit

ADC. The chosen method for conversion is best for converting

small current signals in the presence of an AC periodic noise. A

100ms integration time, for instance, highly rejects 50Hz and

60Hz power line noise simultaneously. See “Integration and

Conversion Time” on page 7.

The built-in ADC offers user flexibility in integration time or

conversion time. There are two timing modes: Internal Timing

Mode and External Timing Mode. In Internal Timing Mode,

integration time is determined by an internal oscillator (fOSC),

and the n-bit (n = 4, 8, 12, 16) counter inside the ADC. In

External Timing Mode, integration time is determined by the

time between two consecutive I2C External Timing Mode

commands. A good balancing act of integration time and

resolution (depending on the application) is required for optimal

results.

The ADC has I2C programmable range select to dynamically

accommodate various lighting conditions. For very dim

conditions, the ADC can be configured at its lowest range

(Range 1) in the ambient light sensing.

Low-Power Operation

The ISL29023 initial operation is at the power-down mode

after a supply voltage is provided. The data registers contain

the default value of 0. When the ISL29023 receives an I2C

command to do a one-time measurement from an I2C

master, it will start ADC conversion with light sensing. It will

go to the power-down mode automatically after one

conversion is finished and keep the conversion data

available for the master to fetch anytime afterwards. The

ISL29023 will continuously do ADC conversion with light

sensing if it receives an I2C command of continuous

measurement. It will continuously update the data registers

with the latest conversion data. It will go to the power-down

mode after it receives the I2C command of power-down.

Ambient Light and IR Sensing

There are four operational modes in ISL29023: Programmable

ALS once with auto power-down, programmable IR sensing

once with auto power-down, programmable continuous ALS

sensing and programmable continuous IR sensing. These four

modes can be programmed in series to fulfill the application

needs. The detailed program configuration is listed in

“Command Register I 00(hex)” on page 5.

When the part is programmed for ambient light sensing, the

ambient light with wavelength within the “Ambient Light

Sensing” spectral response curve in Figure 5 is converted

into current. With ADC, the current is converted to an

unsigned n-bit (up to 16 bits) digital output.

When the part is programmed for infrared (IR) sensing, the

IR light with wavelength within the “IR Sensing” spectral

response curve in Figure 5 is converted into current. With

ADC, the current is converted to an unsigned n-bit (up to

16-bits) digital output.

Interrupt Function

The active low interrupt pin is an open drain pull-down

configuration. The interrupt pin serves as an alarm or

monitoring function to determine whether the ambient light

level exceeds the upper threshold or goes below the lower

threshold. It should be noted that the function of ADC

conversion continues without stopping after interrupt is

asserted. If the user needs to read the ADC count that

triggers the interrupt, the reading should be done before the

data registers are refreshed by the following conversions.

The user can also configure the persistency of the interrupt

pin. This reduces the possibility of false triggers, such as

noise or sudden spikes in ambient light conditions. An

unexpected camera flash, for example, can be ignored by

setting the persistency to 8 integration cycles.

I2C Interface

There are eight 8-bit registers available inside the ISL29023.

The two command registers define the operation of the

device. The command registers do not change until the

registers are overwritten. The two 8-bit data Read Only

registers are for the ADC output. The data registers contain

the ADC's latest digital output, or the number of clock cycles

in the previous integration period.

The ISL29023’s I2C interface slave address is internally hard-

wired as 1000100. When 1000100x with x as R or W is sent

after the Start condition, this device compares the first 7 bits of

this byte to its address and matches.

Figure 1 shows a sample one-byte read. Figure 2 shows a

sample one-byte write. The I2C bus master always drives the

SCL (clock) line, while either the master or the slave can drive

the SDA (data) line. Figure 2 shows a sample write. Every I2C

transaction begins with the master asserting a start condition

(SDA falling while SCL remains high). The following byte is

driven by the master, and includes the slave address and

read/write bit. The receiving device is responsible for pulling

SDA low during the acknowledgement period. Every I2C

transaction ends with the master asserting a stop condition

(SDA rising while SCL remains high).

For more information about the I2C standard, please consult

the Philips™ I2C specification documents.

4

FN6691.0

March 3, 2009

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