ISL29018 Datasheet, PDF (10/15 Pages) Intersil Corporation – Digital Ambient Light Sensor and Proximity Sensor with Interrupt Function

ISL29018
not detect an optically black object that reflects no light.
However, ISL29018 is sensitive enough to detect a black ESD
foam, which reflects slightly less than 1% of IR, as shown in
Figure 9. For biological objects, blonde hair reflects more than
brunette hair, as expected and shown in Figure 11. Also notice
that skin tissue is much more reflective than hair. IR
penetrates into the skin and is reflected or scattered back
from within. As a result, the proximity count peaks at contact
and monotonically decreases as skin moves away. This
characteristic is very different from that of a plain paper
reflector.
Interrupt Function
Depending on the mode of operation set by Bits 7, 6 and 5 of
command register 00 hex, the upper and lower interrupt
thresholds are for either ambient light level or proximity
detection. After each change of mode of operation, it is
expected a new set of thresholds are loaded to interrupt
registers 04, 05, 06 and 07 hex for proper interrupt detection.
Also, the interrupt persist counter will be reset to 0 when the
mode of operation is changed.
V_DD Power-up and Power Supply Considerations
Upon power-up, please ensure a VDD slew rate of 0.5V/ms
or greater. After power-up, or if the user’s power supply
temporarily deviates from our specification (2.25V to 3.63V),
Intersil recommends the user write 0x00 to two registers:
0x08, 0x00 (in that order), wait ~1ms or more and then
rewrite all registers to the desired values.
LED Modulation for Proximity Detection
ISL29018 offers two ways to modulate the LED in the
Proximity Detection mode - DC or 360kHz (with 50% duty
cycle) by bit 6 of register 01h. At the IRDR pin, there are four
different IRDR LED currents; 12.5, 25, 50, and 100mA
outputs selectable by bits 4 and 5 of register 01h. With the
LED running in the DC mode, the proximity detection is twice
as sensitive but consumes 2 times more current. The
sensitivity of LED 50mA, DC 50mA is identical to that of
100mA, 360kHz modulation. Please note that the ISL29018
does not include a LED.
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 360kHz 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 ISL29018 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
capacitor 0.1µF, placed close to the device.
Typical Circuit
A typical application for the ISL29018 is shown in Figure 4.
The ISL29018’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.
10
FN6619.1
February 11, 2010