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MAX44000
Ambient and Infrared Proximity Sensor
The IC operates from a V DD of 1.7V to 3.6V and con-
sumes just 5 F A current in ALS mode and 7 F A time-aver-
aged in proximity mode. The on-chip IR proximity detec-
tor DC ambient rejection circuitry is synchronized with
pulsing of an integrated IR LED transmitter to improve
noise immunity from external fluctuating IR sources.
This scheme also reduces IR LED power consumption
compared to alternate methods and eliminates red-glow
problems with the use of 850nm IR LEDs; power con-
sumption is reduced to 11 F A (time averaged), includ-
ing the current consumption of an external IR LED. An
on-chip programmable interrupt function eliminates the
need to continually poll the device for data, resulting in a
significant power saving.
Ambient Light Sensing
The ambient light sensors are designed to detect bright-
ness in the same way as human eyes do. To achieve this,
the light sensor needs to have a spectral sensitivity that
is identical to the photopic curve of the human eye (see
Figure 1). Small deviations from the photopic curve can
affect perceived brightness by ambient light sensors to
be wildly different. However, there are practical difficul-
ties in trying to reproduce the ideal photopic curve in a
small cost-efficient package. The IC instead uses two
different types of photodiodes (a green and an infrared)
that have different spectral sensitivities—each of which
is amplified and subtracted on-chip with suitable gain
120
100
coefficients so that the most extreme light sources (fluo-
rescent and incandescent) are well matched to a com-
mercial illuminance lux meter.
The photopic curve represents a typical human eye’s
sensitivity to wavelength. As can be seen in Figure 1
and Figure 2, its peak sensitivity is at 555nm (green).
The human eye is insensitive to infrared (> 700nm) and
ultraviolet (< 400nm) radiation.
Variation between light sources can extend beyond the
visible spectral range. For example, fluorescent and
incandescent light sources with similar visible brightness
(lux) can have substantially different IR radiation content
(since the human eye is blind to it). Since this infrared
radiation can be picked up by silicon photodiodes, dif-
ferences in light spectra can affect brightness measure-
ment of light sensors. For example, light sources with
high IR content, such as an incandescent bulb or sun-
light, would suggest a much brighter environment than
our eyes would perceive them to be. Other light sources
such as fluorescent and LED-based systems have very
little infrared content. The IC incorporates on-chip com-
pensation techniques to minimize these effects and still
output an accurate lux response in a variety of lighting
conditions.
On-chip user-programmable green channel and IR chan-
nel gain trim registers allow the light sensor response to
be tailored to the application, such as when the light sen-
sor is placed under dark or colored glass.
120
100
80
STANDARD ALS
(GREEN-RED)
80
GREEN CHANNEL
RED CHANNEL
CIE CURVE
60
40
20
0
270 370 470 570 670 770 870 970 1070
WAVELENGTH (nm)
Figure 1. Spectral Response Compared to Ideal Photopic
Curve
8
60
40
20
0
270 370 470 570 670 770 870 970 1070
WAVELENGTH (nm)
Figure 2. Green Channel and IR Channel Response at
Identical Gains on a Typical MAX44000
Maxim Integrated
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