ISL29000 Datasheet, PDF (5/7 Pages) Intersil Corporation – Ambient Light Photo Detect IC

ISL29000
TABLE 1. V_DD = 5V, MAXIMUM OUTPUT VOLTAGE = 4.7V
ILLUMINATION RANGE
(LUX)
RLOAD
(kΩ)
CURRENT OUT
(µA)
0 to 10
7830
0 to 0.6
0 to 200
392
0 to 12
0 to 500
157
0 to 30
0 to 1,000
80
0 to 60
0 to 10,000
8.00
0 to 600
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 ISL29000 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
ISL29000 for a given exposure of light.
The example in Figure 9 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 1.25V to drive the input of an LED
driver controller. The 0.25V represents the minimum LED
brightness and 1.25V represents the maximum. The 1st step
would be to determine the ratio of R₁ and R₂:
R₁
=
R₂
×
⎛
⎝
--³----^.-⁰----^V----
0.25 V
–
1_⎠⎞
=
11 × R₂
(EQ. 4)
3V TO 5V
SUPPLY VOLTAGE
3V DC VOLTAGE
VDO
ISL29000
EN
OUT
GND
R₂
110k
TO INVERTER BRIGHTNESS
INPUT OR LED DRIVER
CONTROLLER
R₁
10k
C₁
25µF
Next, the value of R₂ can be calculated based on the
maximum output current coming from the ISL29000 under
the application's maximum light exposure. Suppose the
current has been determined to be about 125µA. Thus, R₂
can be calculated approximately using Equations 5 and 6:
R₂
=
⎛
⎝
1^--1--2^-.--25---5-μ^---V-A^{--⎠⎞}
=
10 k Ω
(EQ. 5)
and
R₁ = 11 × R₂ = 110kΩ
(EQ. 6)
In Figure 10, user adjustable bias control has been added to
allow control over the minimum and maximum output
voltage. This allows the user to adjust the output brightness
to personal preference over a limit range via the 3V PWM
control.
3V TO 5V
SUPPLY VOLTAGE
3V PWM CONTROL
VDO
ISL29000
EN
OUT
GND
R₂
110k
TO INVERTER BRIGHTNESS
INPUT OR LED DRIVER
CONTROLLER
R₁
C₁
10k _25µF
FIGURE 10. AUTOMATIC DIMMING SOLUTION WITH
ADJUSTABLE BIAS CONTROL
Figure 11 shows how a fully manual override can be quickly
added by using the EN pin.
3V TO 5V
SUPPLY VOLTAGE
3V PWM CONTROL
VDO
ENABLE/
DISABLE
CONTROL
ISL29000
EN
OUT
GND
R₂
110k _{TO INVERTER}
BRIGHTNESS
INPUT OR LED
DRIVER
CONTROLLER
R₁
10k
C₁
25µF
FIGURE 9. AUTOMATIC DIMMING SOLUTION
5
FIGURE 11. AUTOMATIC DIMMING SOLUTION WITH
ADJUSTABLE BIAS CONTROL AND MANUAL
OVERRIDE
FN6117.6
September 2, 2008