ISL29033

6

FN7656.2

February 25, 2013

Principles of Operation

Photodiodes and ADC

The ISL29033 contains two photodiode arrays that convert light into

current. The spectral response for ambient light sensing and

infrared (IR) sensing is shown in Figure 8 in the “Typical

Performance Curves” section on page 12. 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

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 9.

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

12, 16) counter inside the ADC. In External Timing Mode, integration

External Timing Mode commands. A good balance of integration

time and resolution (depending on application) is required for

optimal results.

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 ISL29033 initial operation is at the power-down mode after a

supply voltage is provided. The data registers contain the default

conversion with light sensing. It goes to power-down mode

automatically after one conversion is finished and keeps the

conversion data available for the master to fetch anytime

afterwards. The ISL29033 continuously does ADC conversion

measurement. It continuously updates the data registers with

the latest conversion data. It goes to power-down mode after it

Ambient Light

There are four operational modes in ISL29033: 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 shown in “BLOCK DIAGRAM” on page 1.

When the part is programmed for ambient light sensing, the

ambient light with wavelength within the “Ambient Light

Sensing” spectral response curve in Figure 8 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 8 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. Note 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, reading should be done before the data

registers are refreshed by subsequent 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 eight

integration cycles.

ALS Ranges Considerations

When measuring ALS counts higher than 30000 counts on

Range 1 of the 16-bit ADC, switch to Range 2 (change [1 to 0]

bits of Register 1 from 00 to 01), and re-measure the ALS counts

and other data to change to Range 3 and Range 4. This

recommendation pertains only to applications in which light

incident on the sensor is IR-heavy and is distorted by tinted glass

that increases the ratio of infrared to visible light.

Considerations

After power-up, or if the power supply temporarily deviates from

Data Valid Time

0.9

µs

Data Valid Acknowledge Time

0.9

µs

Noise Margin at the LOW Level

V

Noise Margin at the HIGH Level

V

NOTE:

PARAMETER

DESCRIPTION

CONDITION

MIN

(Note 6)

TYP

MAX

(Note 6)

UNIT