ISL29035_14 Datasheet, PDF (7/16 Pages) Intersil Corporation – Integrated Digital Light Sensor with Interrupt

ISL29035
Principles of Operation
Photodiodes and ADC
The ISL29035 contains two photodiode arrays, which convert
light into current. The spectral response for ambient light sensing
and IR sensing is shown in Figure 5 on page 6. 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 105ms
integration time, for instance, highly rejects 50Hz and 60Hz
power line noise simultaneously.
The integration time of the built-in ADC is determined by the
internal oscillator, and the n-bit (n = 4, 8, 12, 16) counter inside
the ADC. 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 0) in the ambient light sensing.
Low-Power Operation
The ISL29035 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 ISL29035 receives an I²C command to do a
one-time measurement from an I²C master, it will start ADC
conversion with light sensing. It will go to the power-down mode
automatically after one conversion is finished and keep the
conversion data available for the master to fetch anytime
afterwards. The ISL29035 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 to the power-down mode
after it receives the I²C command of power-down.
Ambient Light and IR Sensing
There are four operational modes in ISL29035: 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 10.
When the part is programmed for ambient light sensing, the
ambient light with wavelength within the “Ambient Light
Sensing” spectral response curve in Figure 14 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 14 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.
Serial Interface
The ISL29035 supports the Inter-Integrated Circuit (I²C) bus data
transmission protocol. The I²C bus is a two-wire serial
bidirectional interface consisting of SCL (clock) and SDA (data).
Both the wires are connected to the device supply via pull-up
resistors. The I²C protocol defines any device that sends data
onto the bus as a transmitter and the receiving device as the
receiver. The device controlling the transfer is a master and the
device being controlled is the slave. The transmitting device pulls
down the SDA line to transmit a “0” and releases it to transmit a
“1”. The master always initiates the data transfer, only when the
bus is not busy, and provides the clock for both transmit and
receive operations. The ISL29035 operates as a slave device in
all applications. The serial communication over the I²C interface
is conducted by sending the most significant bit (MSB) of each
byte of data first.
Start Condition
During data transfer, the SDA line must remain stable while the
SCL line is HIGH. All I²C interface operations must begin with a
START condition, which is a HIGH-to-LOW transition of SDA while
SCL is HIGH (refer to Figure 11 on page 8). The ISL29035
continuously monitors the SDA and SCL lines for the START
condition and does not respond to any command until this
condition is met (refer to Figure 11). A START condition is ignored
during the power-up sequence.
Stop Condition
All I²C interface operations must be terminated by a STOP
condition, which is a LOW-to-HIGH transition of SDA while SCL is
HIGH (refer to Figure 11). A STOP condition at the end of a
read/write operation places the device in its standby mode. If a
stop is issued in the middle of a Data byte, or before 1 full Data
byte + ACK is sent, then the serial communication of the
ISL29035 resets itself without performing the read/write. The
contents of the array are not affected.
Acknowledge
An acknowledge (ACK) is a software convention used to indicate
a successful data transfer. The transmitting device releases the
SDA bus after transmitting 8-bits. During the ninth clock cycle,
the receiver pulls the SDA line LOW to acknowledge the reception
of the eight bits of data (refer to Figure 11). The ISL29035
responds with an ACK after recognition of a START condition
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FN8371.1
November 12, 2014