3
FN7464.5
August 8, 2008
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 8
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
(ADC). An
I
2
C command mode determines which photodiode
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 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 8 and “Noise
Rejection” on page 9.
The built-in ADC offers the 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 (f
OSC
), 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 I
2
C External
Timing Mode commands. See “External Timing Mode” on
page 7. A good balancing act of integration time and resolution
depending on the application is required for optimal results.
The ADC has four I
2
C programmable range select to
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.
I
2
C Interface
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.
The ISL29003’s I
2
C interface slave address is hardwired
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
sample one-byte write. Figure 3 shows a sync_iic timing
diagram sample for externally controlled integration time.
The I
2
C 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 I
2
C 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 I
2
C transaction ends with the master asserting a stop
condition (SDA rising while SCL remains high).
For more information about the I
2
C standard, please consult
the Philips
®
I
2
C specification documents.
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) 100kΩ resistor
4INT
Interrupt pin; LO for interrupt/alarming. The INT pin is an open drain.
5SCLI
2
C serial clock The I
2
C bus lines can be pulled above VDD, 5.5V max.
6SDAI
2
C serial data
ISL29003
