ISL29028IROZ Datasheet, PDF (9/16 Pages) Intersil Corporation – Low Power Ambient Light and Proximity Sensor with Intelligent Interrupt and Sleep Modes

ISL29028
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
The proximity sensor is an 8-bit ADC which operates in a
similar fashion. When proximity sensing is enabled, the
IRDR pin will drive a user-supplied infrared LED, the
emitted IR reflects off an object (i.e., a human head) back
into the ISL29028, 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 ISL29028 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 ISL29028 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 digitized by the same ALS
ADC. The result of an IR conversion is strongly related to
the amount of IR energy incident on our sensor, but 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 for 0.1ms by the built-in IR LED
driver through the IRDR pin. The amplitude of the IR LED
current depends on Register 1 bit 3: PROX_DR. If this bit
is low, the load will see a fixed 110mA current pulse. If
this bit is high, the load on IRDR will see a fixed 220mA
current pulse as seen in Figure 4.
220mA
(PROX_DR = 1)
110mA
(PROX_DR = 0)
PIN 8 - IRDR
(IRDR IS HI-Z WHEN
NOT DRIVING)
FIGURE 4. CURRENT DRIVE MODE OPTIONS
When the IR from the LED reaches an object and gets
reflected back into the ISL29028, the reflected IR light is
converted into current as per the IR spectral response
shown in Figure 7. One entire proximity measurement
takes 0.54ms for one conversion (which includes 0.1ms
spent driving the LED), and the period between proximity
measurements is decided by PROX_SLP (sleep time) in
Register 1 Bits 6:4.
Average LED driving current consumption is given by
Equation 1.
I _{l R D R ;A V E}
=
I_{--l--R----D----R-----;-P----E----A----K-----}×_-----1_---0_---0_----μ_----s_-
T_SLEEP
(EQ. 1)
A typical IRDR scheme is 220mA amplitude pulses every
800ms, which yields 28μA DC.
Total Current Consumption
Total current consumption is the sum of I_DD and I_IRDR.
The IRDR pin sinks current (as shown in Figure 4) and
the average IRDR current can be calculated using
Equation 1 above. I_DD depends on voltage and the
mode-of-operation as seen in Figure 11.
9
FN6780.2
November 4, 2011