MAX44000 Maxim, MAX44000 Datasheet - Page 17

• Manufacturer Part Number: MAX44000
• Description: MAX44000 combines a wide-dynamic range ambient light sensor with an integrated infrared proximity sensor, making it a perfect solution for touch-screen portable devices
• Manufacturer: Maxim

Typical applications involve placing the IC behind a
glass with a small semitransparent window placed above
it. Use the photodiode sensitive area as shown in Figure
3 to properly position the window above the part.
The part comes equipped with internal gain trim regis-
ters for the green and IR ALS photodiodes. By suitably
choosing the gains for these channels, accurate ambient
light readings can be generated in all lighting conditions
irrespective of the type of glass the part is used under.
This is especially useful for black-glass applications,
where for cosmetic reasons, the part is placed behind
a black film to hide its presence, and this film has the
peculiar property of attenuating most ambient light, but
passing through infrared radiation.
In standard ALS mode, the green channel and infrared
channel readings are internally subtracted. Since one is
observing only the difference in two separate ADC mea-
surements, wrong readings can be obtained if one of the
channels becomes saturated, while the other channel
continues to rise. Since both the green photodiode also
picks up a lot of the infrared signal, this saturation can
occur much before the maximum expected full-scale
range in certain lighting conditions. For example, under
incandescent light, there is a lot more infrared optical
power than in the visible spectral range. In these situa-
tions, the green channel can saturate much earlier than
511 lux in the most sensitive range. To assist the user in
detecting these conditions, an OFL bit is provided that
alerts the user of an overrange condition. This bit also
triggers an ALS interrupt if it has been enabled.
The IC integrates a novel proximity sensor interface
circuit with a robust built-in ambient IR cancellation
scheme. The internal DC IR rejection circuit eliminates
problems of ADC saturation in the presence of strong
ambient infrared radiation, such as bright sunlight.
Further, the proximity sensor uses a single-pulse scheme
for the IR transmitter that eliminates red-glow problems
seen in competing solutions to drive 850nm IR LEDs,
while also reducing average IR LED power consumption
to less than 0.1% of the IR LED peak current.
Applications Information
Proximity Sensing Applications
______________________________________________________________________________________
Ambient Sensing Applications
Ambient and Infrared Proximity Sensor
Ambient interrupt is enabled by setting bit 0 of register
0x01 to 1 and proximity interrupt is enabled by setting
bit 1 of register 0x01 to 1 (see Table 1 and Table 2). The
interrupt pin, INT, is an open-drain output and pulls low
when an interrupt condition occurs (e.g., when ambient
lux readings exceed threshold limits for a period greater
than that set by the Time register). The interrupt status bit
is cleared automatically if register 0x00 is read or if the
interrupts are disabled.
A PWRON interrupt bit is set to alert the master of a chip
reset operation in case of a power-supply glitch that can
happen on smartphones that place the light sensor on a
flex with a small connector.
It is best to utilize the interrupt pin on the IC to alert the
master to come and read measurements from the IC. This
eliminates the need for the microcontroller (I
to continually poll the device for information. Due to the
use of pullup resistors on the I
activity can reduce power consumption substantially. In
addition, this frees up the microcontroller resources to
service other background processes to improve device
performance. The wide variety of smarts available on the
chip, such as the ability to set the threshold levels and to
count persist timer limits, allow the part to operate in an
autonomous mode most of the time.
Figure 3. Photodiode Location
1.226mm
0.39mm
GND
DRV 3
V
CC
1
2
0.753mm
0.492mm
PHOTO-
DIODE
2mm
2
C bus, minimizing I
Interrupt Operation
MAX44000
TOP VIEW
2
C master)
6 SDA
5 SCL
4 INT
2
C bus
2mm
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