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# ISL29008IROZ View Datasheet(PDF) - Intersil

 Part Name Description Manufacturer ISL29008IROZ Small, Low Power, Current-Output Ambient Light Photo Detect IC Intersil ISL29008IROZ 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