ISL29006IROZ-T7 View Datasheet(PDF) - Intersil

Part Name

Description

Manufacturer

ISL29006IROZ-T7

Small, Low Power, Current-Output Ambient Light Photo Detect IC

Intersil 

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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