ISL29033 Datasheet, PDF (6/15 Pages) Intersil Corporation – Simple output code directly proportional to lux

ISL29033
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 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 (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 a 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 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
balance of integration time and resolution (depending on
application) is required for optimal results.
The ADC has an 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 ISL29033 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 ISL29033 receives an I²C command to do a
one-time measurement from an I²C master, it starts an ADC
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 the ADC conversion
with light sensing if it receives an I²C command of continuous
measurement. It continuously updates the data registers with
the latest conversion data. The ISL29033 goes to power-down
mode after it receives the I²C command of power-down.
Ambient Light
There are two operational modes in ISL29033: programmable
continuous ALS sensing and programmable continuous IR
sensing. These two modes can be programmed in series to fulfill
the application needs. The detailed program configuration is
shown in the Figure 1 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 remeasure 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.
V_DD Power-Up and Power Supply
Considerations
Upon power-up, ensure a V_DD slew rate of 0.5V/ms or greater.
After power-up, or if the power supply temporarily deviates from
specification (2.25V to 3.63V), the following step is
recommended: write 0x00 to register 0x00. Wait a few seconds
and then rewrite all registers to the desired values. A hardware
reset method can be used, if preferred, instead of writing to the
test registers. For this method, set V_DD = 0V for 1 second or more,
power back up at the required slew rate and write the registers to
the desired values.
Power-Down
To put the ISL29033 into a power-down state, the user can set
[7 to 5] bits to 0 in Register 0. Or more simply, set all of
Register 0 to 0x00.
I²C Interface
There are eight 8-bit registers available inside the ISL29033. The
two command registers define the operation of the device. The
command registers do not change until the registers are
overwritten. The two 8-bit data read-only registers are for the ADC
output. The data registers contain the ADC's latest digital output,
or the number of clock cycles in the previous integration period
(Figure 2 on page 7).
The ISL29033 I2C interface slave address is internally hard-wired as
1000100. When 1000100x, with x as R or W, is sent after the start
condition, the device compares the first seven bits of this byte to its
address and matches. Figure 3 on page 7 shows a sample one-
byte read and Figure 4 on page 8 shows a sample one-byte write.
The I²C bus master always drives the SCL (clock) line, while either
the master or the slave can drive the SDA (data) line. Every I²C
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FN7656.5
September 28, 2016