ALS-PDIC17-79NB-TR8_15 Datasheet, PDF (13/19 Pages) Everlight Electronics Co., Ltd – Digital Ambient Light Sensor

DATASHEET
SMD  I²C Digital Ambient Light Sensor
ALS-PDIC17-79NB/TR8
Noise Rejection and Integration Time
In general, integrating type ADC’s have an excellent noise rejection characteristics for periodic noise sources
whose frequency is an integer multiple of the integration time. For instance, a 60Hz AC unwanted signal’s sum from 0ms
to n*16.66ms (n = 1, 2...ni) is zero. Similarly, setting the ALS-PDIC17-79NB integration time to an integer multiple of
periodic noise signal greatly improves the light sensor output signal in the presence of noise. The integration time, Tint,
of the ALS-PDIC17-79NB is set by an external resistor Rext. The maximum detection range is inversely proportional to
the integration time; that means the longer integration time the lower detection range.
Rext
(KΩ)
50
(min.)
100
(recommended)
200
300
400
(max.)
Integration time
( mS )
50
100
200
300
400
Detection range
( Lux )
88,400
44,200
22,200
14,500
11,100
Resolution
( Lux / Count )
2.7
1.35
0.68
0.45
0.34
Table 4 Rext Resistor Selection Guide
In order to achieve both 60Hz and 50Hz AC rejection, the integration time needs to be adjusted to coincide with
an integer multiple of the AC noise cycle times. To determine a suitable integration time, Tint, that will ignore the
presence of both 60Hz and 50Hz noise, users can use the formula:
Tint = n(1/60Hz) = m(1/50Hz), where n and m are integers.
n/m = 60Hz/50Hz = 6/5.
The first instance of integer values at which Tint rejects both 60Hz and 50Hz is when m = 5, and n = 6, thus,
Tint = 6(1/60Hz) = 5(1/50Hz) = 100ms,
Rext = Tint* (100kΩ/100ms) = 100kΩ, (see Table 4)
By populating Rext = 100kΩ, ALS-PDIC17-79NB defaults to 100ms integration time in continuous operation
mode, and will reject the presence of both 60Hz and 50Hz power line signals. When working in one-time integration
mode, the master must control the integration time to be an integer multiple of 100ms.
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