ISL29023_14 Datasheet, PDF (5/14 Pages) Intersil Corporation – Integrated Digital Light Sensor with Interrupt

ISL29023
Typical Performance Curves (Continued)
90
ALS SENSING
10,000 Lux
85
80
75
70
65
60
-40 -20 0
20 40 60 80 100 120
TEMPERATURE (°C)
FIGURE 9. SUPPLY CURRENT vs TEMPERATURE IN ALS SENSING
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 4, on page 4. 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.
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 (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 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 the ADC
conversion with light sensing. It will go into 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 into power-down mode after
it receives the I²C command.
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-I Register (Address:
0x00)” on page 8.
When the part is programmed for ambient light sensing, the
ambient light with wavelength within the “Ambient Light
Sensing” spectral response curve in Figure 4 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 4 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.
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5
FN6691.4
May 1, 2014