ISL29030A_14 Datasheet, PDF (9/16 Pages) Intersil Corporation – Low Power Ambient Light and Proximity Sensor with Intelligent Interrupt and Sleep Modes - Analog and Digital Out

ISL29030A
Principles of Operation
I²C Interface
The ISL29030A I²C interface slave address is internally hardwired
as 0b1000100.
Figure 2 shows a sample one-byte read. 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 transaction begins
with the master asserting a start condition (SDA falling while SCL
remains high). The first transmitted byte is initiated by the
master and includes seven address bits and a R/W bit. The slave
is responsible for pulling SDA low during the ACK bit after every
transmitted byte.
Each I²C transaction ends with the master asserting a stop
condition (SDA rising while SCL remains high).
For more information about the I²C standard, please consult the
Philips^™ I²C specification documents.
Photodiodes and ADCs
The ISL29030A contains two photodiode arrays that convert
photons (light) into current. The ALS photodiodes are constructed to
mimic the human eye wavelength response curve to visible light
(see Figure 7). The ALS photodiode current output is digitized by a
12-bit ADC in 100ms. These 12 bits can be accessed by reading
from I²C registers 0x9 and 0xA when the ADC conversion is
completed.
The ALS converter is a charge-balancing, integrating, 12-bit ADC.
Charge-balancing is best for converting small current signals in the
presence of periodic AC noise. Integrating over 100ms highly rejects
both 50Hz and 60Hz light flicker by picking the lowest-integer
number of cycles for both 50Hz/60Hz frequencies.
The proximity sensor is an 8-bit ADC that operates in a similar
fashion. When proximity sensing is enabled, the IRDR pin drives
a user-supplied infrared LED, the emitted IR reflects off an object
(i.e., a human head) back into the ISL29030A, and a sensor
converts the reflected IR wave to a current signal in 0.54ms. The
ADC subtracts the IR reading before and after the LED is driven
(to remove ambient IR such as sunlight) and converts this value
to a digital count stored in Register 0x8.
The ISL29030A is designed to run two conversions concurrently: a
proximity conversion, and an ALS (or IR) conversion. Please note
that because of the conversion times, the user must let the ADCs
perform one full conversion first before reading from I²C
Registers PROX_DATA (wait 0.54ms) or ALSIR_DT1/2 (wait
100ms). The timing between ALS and Prox conversions is
arbitrary, as shown in Figure 3. The ALS runs continuously, with
new data available every 100ms. The proximity sensor runs
continuously, with a time between conversions decided by
PROX_SLP (Register 1 Bits [6:4]).
Ambient Light and IR Sensing
The ISL29030A is set for ambient light sensing when Register bit
ALSIR_MODE = 0 and ALR_EN = 1. The light-wavelength response of
the ALS appears as shown in Figure 6. ALS measuring mode (as
opposed to IR measuring mode) is set by default.
When the part is programmed for infrared (IR) sensing
(ALSIR_MODE = 1; ALS_EN = 1), infrared light is converted into a
current and is digitized by the same ALS ADC. The result of an IR
conversion is strongly related to the amount of IR energy incident
on the sensor, but it is unitless and is referred to in digital counts.
Proximity Sensing
When proximity sensing is enabled (PROX_EN = 1), the external
IR LED is driven through the IRDR pin for 0.1ms by the built-in IR
LED driver. The amplitude of the IR LED current depends on
Register 1 bit 3: PROX_DR. If this bit is low, the load sees a fixed
110mA current pulse. If this bit is high, the load on IRDR sees a
fixed 220mA current pulse, as shown in Figure 4.
ALS
ACTIVE
ALS CONVERSION
TIME = 100ms
(FIXED)
SEVERAL µs BETWEEN
CONVERSIONS
100ms
100ms
100ms
100ms
100ms
PROX
SENSOR
ACTIVE
0.54ms FOR
PROX
CONVERSION
TIME
TIME
IRDR
(CURRENT
DRIVER)
SERIES OF
CURRENT PULSES
TOTALING 0.1ms
TIME
SLEEP TIME
(PROX_SLP)
FIGURE 3. TIMING DIAGRAM FOR PROX/ALS EVENTS - NOT TO SCALE
9
FN7722.2
November 12, 2012