ISL29010 Intersil Corporation, ISL29010 Datasheet - Page 8

• Manufacturer Part Number: ISL29010
• Description: Light-to-Digital Output Sensor
• Manufacturer: Intersil Corporation

INTEGRATION TIME IN EXTERNAL TIMING MODE
This timing mode is programmed in the command register
00(hex) Bit 5. External Timing Mode is recommended when
integration time can be synchronized to an external signal
such as a PWM to eliminate noise.
To read the light count DATA output, the device needs three
sync_I
sync_I
The 2nd sync_I
and starts the conversion of diode array 2. The 3rd sync_I
pules ends the conversion of diode array 2, outputs the light
count DATA, and starts over again to commence conversion
of diode array 1.
The integration time, t
intervals between the three sync pulses. t
by Equation 12:
where k
from Timer data register and f
operating frequency.
The internal oscillator, f
internal and external timing modes, with the same
dependence on R
the number of clock cycles per integration is no longer fixed
at 2
integration time, and is limited to 2
avoid erroneous lux readings the integration time must be
short enough not to allow an overflow in the counter register.
Noise Rejection
In general, integrating type ADC’s have 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 k*16.66ms (k = 1,2...k
device’s integration time to be an integer multiple of the
periodic noise signal greatly improves the light sensor output
signal in the presence of noise.
Flat Window Lens Design
A window lens will surely limit the viewing angle of the
ISL29010. The window lens should be placed directly on top
of the device. The thickness of the lens should be kept at
minimum to minimize loss of power due to reflection and
also to minimize loss due to absorption of energy in the
t
t
INT
INT
www.DataSheet4U.com
f
Range1 or Range2.
f
Range3 or Range4.
OSC
OSC
n
<
. The number of clock cycles varies with the chosen
=
65,535
----------------- -
2
2
f
k
-------------- -
f
C commands to complete one measurement. The 1st
C command starts the conversion of the diode array 1.
OSC
OSC
OSC
= 327kHz*100kΩ/R
= 655kHz*100kΩ/R
OSC
is the number of internal clock cycles obtained
2
C completes the conversion of diode array 1
EXT
. However, in External Timing Mode,
INT
OSC
, is the sum of two identical time
EXT
EXT
, operates identically in both the
i
OSC
) is zero. Similarly, setting the
8
. When Range/Gain is set to
. When Range/Gain is set to
16
is the internal I
= 65,536. In order to
INT
is determined
2
C
(EQ. 12)
(EQ. 13)
2
C
ISL29010
plastic material. A thickness of t = 1mm is recommended for
a window lens design. The bigger the diameter of the
window lens, the wider the viewing angle is of the ISL29010.
Table 12 shows the recommended dimensions of the optical
window to ensure both 35° and 45° viewing angle. These
dimensions are based on a window lens thickness of 1.0mm
and a refractive index of 1.59.
Window with Light Guide Design
If a smaller window is desired while maintaining a wide
effective viewing angle of the ISL29010, a cylindrical piece of
transparent plastic is needed to trap the light and then focus
and guide the light on to the device. Hence the name light
guide which is also known as light pipe. The pipe should be
placed directly on top of the device with a distance of
D1 = 0.5mm to achieve peak performance. The light pipe
should be a minimum of 1.5mm in diameter to ensure that
whole area of the sensor will be exposed. See Figure 5.
t = 1
D1
D
D
* All dimensions are in mm.
TABLE 12. RECOMMENDED DIMENSIONS FOR A FLAT
E =
D
LENS
TOTAL
WINDOW LENS
ISL29013
TOTAL
1.5
2.0
2.5
3.0
3.5
DATA
2
15
x 2000
Thickness of lens
Distance between ISL29010 and inner edge of lens
Diameter of lens
Distance constraint between the ISL29010 and lens
outer edge
WINDOW DESIGN
FIGURE 4. FLAT WINDOW LENS
0.50
1.00
1.50
2.00
2.50
D1
VIEWING ANGLE
D
LENS
D
LENS
2.25
3.00
3.75
4.30
5.00
∅
@ 35
∅ = VIEWING ANGLE
VIEWING ANGLE
D
LENS
D1
February 13, 2008
t
3.75
4.75
5.75
6.75
7.75
@ 45
D
FN6414.0
TOTAL