3

FN7464.2

December 12, 2006

Principles of Operation

Photodiodes

The ISL29003 contains two photodiodes. Diode1 is sensitive

to both visible and infrared light, while Diode2 is mostly

sensitive to infrared light. The spectral response of the two

diodes are independent from one another. See Figure 7

Spectral Response vs Wavelength in the performance curves

section. The photodiodes convert light to current. Then, the

diodes’ current outputs are converted to digital by a single

built-in integrating type 16-bit Analog-to-Digital Converter

will be converted to a digital signal. Mode1 is Diode1 only.

Mode2 is Diode2 only. Mode3 is a sequential Mode1 and

Mode2 with an internal subtract function (Diode1 - Diode2).

Analog-to-Digital Converter (ADC)

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 Time and Noise Rejection section.

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

conversion time. Two timing modes are available. Internal

Timing Mode and External Timing Mode. In Internal Timing

Mode, integration time is determined by an internal dual speed

oscillator (fosc), and the n-bit (n = 4, 8, 12,16) counter inside the

ADC. In External Timing Mode, integration time is determined

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 ISL29003.

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 44(hex).

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

sample one-byte write. Figure 3 shows a sync_iic timing

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

4INT

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

5SCL

6SDA

ISL29003