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FN6485.0

February 13, 2008

Principles of Operation

Photodiodes

The ISL29013 contains two photodiode arrays which convert

light into current. Some diodes are sensitive to both visible

and infrared light, while the others are only sensitive to

infrared light. Using the infrared portion of the light as

baseline, the visible light can be extracted. The spectral

response vs wavelength is shown in Figure 7 in the “Typical

Performance Curves” on page 11. After light is converted to

current during the light data process, the current output is

converted to digital by a single built-in integrating type

command reads the visible light intensity in counts.

The converter is a charge-balancing integrating type signed

15-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 Time or Conversion Time” on page 7 and “Noise

Rejection” on page 8.

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 dual speed

the ADC. In External Timing Mode, integration time is

Timing Mode commands. See External Timing Mode example.

A good balancing act of integration time and resolution

depending on the application is required for optimal results.

dynamically accommodate various lighting conditions. For

very dim conditions, the ADC can be configured at its lowest

range. For very bright conditions, the ADC can be configured

at its highest range.

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

exceeds the upper threshold or goes below the lower

threshold. The user can also configure the persistency of the

interrupt pin. This eliminates any 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.

There are eight (8) 8-bit registers available inside the ISL29013.

The command and control registers define the operation of the

device. The command and control registers do not change until

the registers are overwritten. There are two 8-bit registers that

set the high and low interrupt thresholds. There are four 8-bit

data Read Only registers. Two bytes for the sensor reading and

another two bytes for the timer counts. The data registers

contain the ADC's latest digital output, and the number of clock

cycles in the previous integration period.

internally as 1000100. When 1000100x with x as R or W is

sent after the Start condition, this device compares the first

seven bits of this byte to its address and matches.

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

diagram sample for externally controlled integration time.

either the master or the slave can drive the SDA (data) line.

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.

condition (SDA rising while SCL remains high).

Pin Descriptions

PIN NUMBER

PIN NAME

DESCRIPTION

1

VDD

Positive supply; connect this pin to a regulated 2.5V to 3.3V supply

2

GND

Ground pin. The thermal pad is connected to the GND pin

3

REXT

External resistor pin for ADC reference; connect this pin to ground through a (nominal) 100k

Ω resistor with

1% tolerance

4INT

Interrupt pin; LO for interrupt/alarming. The INT pin is an open drain.

5SCL

6SDA

ISL29013