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ISL29006IROZ-EVALZ View Datasheet(PDF) - Intersil

Part NameDescriptionManufacturer
ISL29006IROZ-EVALZ Small, Low Power, Current-Output Ambient Light Photo Detect IC Intersil
Intersil Intersil
ISL29006IROZ-EVALZ Datasheet PDF : 11 Pages
1 2 3 4 5 6 7 8 9 10
ISL29006, ISL29007, ISL29008
Application Information
Light-to-Current and Voltage Conversion
The ISL29006, ISL29007 and ISL29008 have
responsiveness that is directly proportional to the intensity of
light intercepted by the photodiode arrays. Conversion rate
is independent of the light sources (fluorescent light,
incandescent light or direct sunlight).
IOUT = ⎝⎛1--1--0-.--60----μl--u-A---x-⎠⎞ × E
(EQ. 1)
Here, IOUT is the output current in µA, and E is the input light
in lux.
For some applications, a load resistor is added between the
output and the ground, as shown in Figure 1. The output
voltage can be expressed in Equation 2:
VOUT
=
IOUT × RL
=
1--1--0-.--60---μ-l--u-A---x-⎠⎞
×
E
×
RL
(EQ. 2)
Here, VOUT is the output voltage and RL is the value of the
external load resistor. The compliance of the ISL29006's
output circuit may result in premature saturation of the
output current and voltage when an excessively large RL is
used. The output compliance voltage is 300mV below the
supply voltage as listed in VO-MAX of the “Electrical
Specifications” table on page 3.
In order to have the linear relationship between the input
light and the output current and voltage, a proper resistor
value (i.e., gain) should be picked for a specific input light
range. The resistor value can be picked according to
Equation 3:
RL
=
(---V----S----U----P-----–-----0---.--3----V----)
1.6 μ A
×
---1----0---0----l-u----x----
ERANGE
(EQ. 3)
Here, VSUP is the supply voltage and ERANGE is the specific
input light range for an application. For example, an indoor
light ranges typically from 0 lux to 1,000 lux. A resistor value
of 270kΩ for 3V supply voltage can be used. For a small light
range, a large resistor value should be used to achieve
better sensitivity; for a large light range, a small resistor
value should be used to prevent non-linear output current
and voltage.
Application Examples
The following examples present from fully automatic to fully
manual override implementations. These guidelines are
applicable to a wide variety of potential light control
applications. The ISL29006, ISL29007 and ISL29008 can be
used to control the brightness input of CCFL inverters.
Likewise, it can interface well with LED drivers. In each
specific application, it is important to recognize the target
environment and its ambient light conditions. The
mechanical mounting of the sensor, light aperture hole size
and use of a light pipe or bezel are critical in determining the
response of the ambient light detector for a given exposure
of light.
The example in Figure 20 shows a fully automatic dimming
solution with no user interaction. Choose R1 and R2 values
for any desired minimum brightness and slope. Choose C1
to adjust response time and to filter 50/60Hz room lighting.
For example, suppose you wish to generate an output
voltage from 0.25V to 1.2V to drive the input of an LED driver
controller. The 0.25V represents the minimum LED
brightness and 1.2V represents the maximum. The 1st step
would be to determine the ratio of R1 and R2 in Equation 4:
R1
=
R2
×
--3----.-0----V----
0.25 V
1⎠⎞
=
11 × R2
(EQ. 4)
3V TO 5V
SUPPLY VOLTAGE
3V DC VOLTAGE
VDD
ISL29006
ISRC
GND
R1
660k
TO INVERTER BRIGHTNESS
INPUT OR LED DRIVER
CONTROLLER
R2
C1
60k 25µF
FIGURE 20.
Next, the value of R2 can be calculated based on the
maximum output current coming from the ISL29006 under
the application's maximum light exposure. Suppose the
current has been determined to be about 2µA. Thus, R2 can
be approximately calculated using Equations 5 and 6:
R2
=
1-2---.-μ-2---AV---⎠⎞
=
60 k Ω
(EQ. 5)
and Equation 6:
R1 = 11 × R2 = 660kΩ
(EQ. 6)
In Figure 20, the 3VDC supply can be replaced with a user
adjustable bias control, such as 3V PWM control to allow
control over the minimum and maximum output voltage.
Figure 21 shows that ISL29006 is used to provide automatic
dimming control.
Short Circuit Current Limit
The ISL29006, ISL29007 and ISL29008 do not limit the
output short circuit current. If the output is directly shorted to
the ground continuously, the output current could easily
increase for a strong input light such that the device may be
damaged. Maximum reliability is maintained if the output
continuous current never exceeds 6mA by adding a load
8
FN6282.1
September 21, 2010
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