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ISL29000IROZ-T7 Datasheet(PDF) 4 Page - Intersil Corporation |
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ISL29000IROZ-T7 Datasheet(HTML) 4 Page - Intersil Corporation |
4 / 7 page 4 FN6117.4 February 9, 2007 Block Diagram Application Information Product Description The ISL29000 is a light-to-current optical sensor combining photodiodes and current amplifiers on a single monolithic IC. The photodiodes are temperature-compensated and their spectrum resembles the human eye response. The output current is directly proportional to the intensity of light falling on the photodiodes. For 100lux of input fluorescent light, the ISL29000 has an output current of 6.5µA. The ISL29000 is housed in an ultra-compact surface mount clear plastic package. Light-to-Current and Voltage Conversion The ISL29000 has a responsiveness that is directly proportional to the intensity of light intercepted by the photodiodes. Although the conversion rate varies depending on the light sources (fluorescent light, incandescent light or direct sunlight), in general for a fluorescent light, the light-to- current conversion is: Here, IOUT is the output current in µA, and LINPUT 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 the following equation: Here, VOUT is the output voltage and RLOAD is the value of the load resistor added. The compliance of the ISL29000's output circuit may result in premature saturation of the output current and voltage when an excessively large RLOAD is used. The output compliance voltage is 300mV below the supply voltage as listed in VO(MAX) of Electrical Specifications on page 2. 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 the following equation: Here, VSUP is the supply voltage, and LRANGE is the specific input light range for an application. For example, an indoor light ranges typically from 0lux to 1,000lux. A resistor value of 45k Ω 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. Resistor Output RLOAD Selection The resistor output, RLOAD, determines the voltage transfer function of the device. The device converts light into current then RLOAD converts the output current to an output voltage. RLOAD can range from 10Ω to 10MΩ depending on the input lux levels. The table below lists RLOAD values to maximize output swing for typical lux range levels. A careful balance of dynamic swing and fast response has to be considered when choosing RLOAD. For faster response, choose a smaller value RLOAD to shunt stray capacitances that may slow down response time. For maximum dynamic range or swing, choose a higher value RLOAD. Although finite, the output impedance of the device is considerably large. Hence, the light-to-current conversion deviation because of resistor loading is infinitesimal. The recommended maximum RLOAD is 10MΩ. Although the device saturates at 10,000lux (IOUT = 600µA), the output current must never exceed 6mA. The voltage output compliance of the device is 300mV below the supply. The output current stops ramping when the output voltage reaches voltage compliance. Pin Descriptions PIN NAME DESCRIPTION 1 VCC Supply, 2.5V to 5.5V 2 GND Ground 3EN Enable 4 NC No connect 5 Output Current output pin ENABLE OUTPUT GND VCC 1 2 5 3 I OUT 61 μA 1000Lux ------------------------ ⎝⎠ ⎛⎞ L INPUT × = (EQ. 1) V OUT I OUT R LOAD × 61 μA 1000Lux ------------------------ ⎝⎠ ⎛⎞ L INPUT R LOAD × × == (EQ. 2) R LOAD V SUP 0.3V – () 61 · μA --------------------------------------- 1000Lux L RANGE ------------------------ × = (EQ. 3) ISL29000 |
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