ISL29015 Datasheet, PDF (8/13 Pages) Intersil Corporation – Integrated Digital Ambient Light Sensor and Proximity Sensor

ISL29015
DATA_IR = β × E_IR
(EQ. 7)
Here, E_IR is the received IR intensity. The constant β
changes with the spectrum of background IR noise like
sunlight and incandescent light. The β also changes with the
ADC’s range and resolution selections.
ADC Output in Proximity Sensing
In the proximity sensing, the ADC output codes, DATA, are
directly proportional to the total IR intensity from the
background IR noise and from the IR LED driven by the
ISL29015.
DATA_PROX = β × E_IR + γ × E_LED
(EQ. 8)
β and E_IR in Equation 8 have the same meanings as in
Equation 7. The constant γ depends on the spectrum of the
used IR LED and the ADC’s range and resolution selections.
E_LED is the IR intensity which is emitted from the IR LED
and reflected by a specific objector to the ISL29015. E_LED
depends on the current to the IR LED and the surface of the
object. E_LED decreases with the square of the distance
between the object and the sensor.
If background IR noise is small, i.e., E_IR can be neglected,
the ADC output directly decreases with the distance. If there
is significant background IR noise, the sequence of the
proximity sensing followed by the IR sensing can be
implemented. The differential reading of ADC outputs from
the proximity and IR sensing has no effect of background
IR noise and directly decreases with the distance between
the object and the sensor. Please refer to “Typical
Performance Curves” on page 10 for ADC output vs
distance. Figure 9 shows ISL29015 configured at 12-bit ADC
resolution, 12.5mA external LED current at 327.7KHz
modulation frequency, detects three different sensing
objects: 92% brightness paper, 18% gray card and ESD
black foam. Figure 10 shows ISL29015 configured at 12-bit
ADC resolution, programmed external LED at 327.7KHz
modulation frequency, detects the same sensing object: 18%
gray card under four different external LED current: 12.5mA,
25mA, 50mA and 100mA to compare the proximity readout
versus distance.
Current Consumption Estimation
The low power operation is achieved through sequential
readout in the serial fashion, as shown in Figure 3, the
device requires three different phases in serial during the
entire detection cycle to do ambient light sensing, infrared
sensing and proximity sensing. The external IR LED will only
be turned on during the proximity sensing phase under user
program controlled current at modulated frequency depends
on user selections. Figure 3 also shows the current
consumption during each ALS, IR sensing and Proximity
sensing phase. For example, at 8-bit ADC resolution the
integration time is 0.4ms. If user programed 50mA current to
supply external IR LED at 327.7kHz modulated frequency,
during the entire operation cycle that includes ALS, IR
sensing and Proximity sensing three different serial phases,
the detection occurs once every 30ms, the average current
consumption including external IR LED drive current can be
calculated from Equation 9:
[(0.05mA + 0.05mA + 1mA + (50mA∗50%))∗0.4ms)]/30ms = 0.35mA
(EQ. 9)
If at a 12-bit ADC resolution where the integration time for
each serial phase becomes 7ms and the total detection time
becomes 100ms, the average current can be calculated from
Equation 10:
[(0.05mA + 0.05mA + 1mA + (50mA^∗50%))^∗7ms)]/100ms = 1.83mA
(EQ. 10)
Suggested PCB Footprint
It is important that the users check the “Surface Mount
Assembly Guidelines for Optical Dual FlatPack No Lead
(ODFN) Package” before starting ODFN product board
mounting.
http://www.intersil.com/data/tb/tb477.pdf
Layout Considerations
The ISL29015 is relatively insensitive to layout. Like other
I²C devices, it is intended to provide excellent performance
even in significantly noisy environments. There are only a
few considerations that will ensure best performance.
Route the supply and I²C traces as far as possible from all
sources of noise. Use two power-supply decoupling
capacitors, 1µF and 0.1µF, placed close to the device.
Typical Circuit
A typical application for the ISL29015 is shown in Figure 4.
The ISL29015’s I²C address is internally hardwired as
1000100. The device can be tied onto a system’s I²C bus
together with other I²C compliant devices.
Soldering Considerations
Convection heating is recommended for reflow soldering;
direct-infrared heating is not recommended. The plastic
ODFN package does not require a custom reflow soldering
profile, and is qualified to +260°C. A standard reflow
soldering profile with a +260°C maximum is recommended.
8
FN6522.0
October 31, 2008