ISL76683 Datasheet, PDF (13/17 Pages) Intersil Corporation – Light-to-Digital Output Sensor with Gain Selection, Interrupt Function

ISL76683
i_I2C = 10kHz _*100ms
i_I2C = 1,000 I²C clock cycles. An external sync_iic command sent
1,000 cycles after another sync_iic command rejects both 60Hz
and 50Hz AC noise signals.
Next, is to pick an arbitrary R_EXT = 100kΩ and to choose the
Gain/Range Mode. For a maximum 500 lux, Range1 is
adequate. From Equation 3:
FSR = 1000 lux ¹¹----⁰⁰----⁰⁰---^kk----^ΩΩ---
FSR = 1000 lux
The effective transfer function becomes:
E
=
-------^D----^A----^T---^A--------
COUNTER
×
1000
lux
DATA is the sensor reading data located in data registers 04(hex)
and 05(hex)
COUNTER is the timer counter value data located in data registers
06(hex) and 07(hex). In this sample problem, COUNTER = 1000.
TABLE 15. SOLUTION 2 SUMMARY TO EXAMPLE DESIGN PROBLEM
DESIGN PARAMETER
VALUE
t_int
R_EXT
Gain/Range Mode
100ms
100kΩ
Range1 = 1000 lux
FSR
1000 lux
# of clock cycles
COUNTER = 1000
Transfer Function
E = -------^D----^A----^T---^A-------- × 1000 lux
COUNTER
IR Rejection
Any filament type light source has a high presence of infrared
component invisible to the human eye. A white fluorescent lamp,
on the other hand has a low IR content. As a result, output
sensitivity may vary depending on the light source. Maximum
attenuation of IR can be achieved by properly scaling the readings
of Diode1 and Diode2. The user obtains data reading from sensor
Diode1 (D1), which is sensitive to visible and IR, then reading from
sensor Diode2 (D2), which is mostly sensitive from IR. The graph in
Figure 2 shows the effective spectral response after applying
Equation 19 of the ISL76683 from 400nm to 1000nm.
Equation 19 describes the method of cancelling IR in internal
timing mode.
D3 = n(D1 – kD2)
(EQ. 19)
Where:
data = lux amount in number of counts less IR presence
D1 = data reading of Diode1
D2 = data reading of Diode2
n = 1.85. This is a fudge factor to scale back the sensitivity up to
ensure Equation 4 is valid.
k = 7.5. This is a scaling factor for the IR sensitive Diode2.
Flat Window Lens Design
A window lens will surely limit the viewing angle of the ISL76683.
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 of loss due to absorption of energy in the 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 ISL76683. Table 16 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 LENS
t
∅
D_TOTAL
D1
ISL76683
D_LENS
∅ = VIEWING ANGLE
FIGURE 15. FLAT WINDOW LENS
Window with Light Guide Design
If a smaller window is desired while maintaining a wide effective
viewing angle of the ISL76683, 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 or 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 have minimum of 1.5mm in
diameter to ensure that whole area of the sensor will be exposed.
See Figure 16.
TABLE 16. RECOMMENDED DIMENSIONS FOR A FLAT WINDOW
DESIGN
D_TOTAL
1.5
D1
0.50
D_LENS @ 35° VIEWING D_LENS @ 45° VIEWING
ANGLE
ANGLE
2.25
3.75
2.0
1.00
3.00
4.75
2.5
1.50
3.75
5.75
3.0
2.00
4.30
6.75
3.5
2.50
5.00
7.75
t=1
D1
D_LENS
D_TOTAL
Thickness of lens
Distance between ISL76683 and inner edge of lens
Diameter of lens
Distance constraint between the ISL76683 and lens
outer edge
*All dimensions are in mm.
13
FN7697.1
January 31, 2011