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ISL29004IROZ-EVALZ Datasheet(PDF) 11 Page - Intersil Corporation |
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ISL29004IROZ-EVALZ Datasheet(HTML) 11 Page - Intersil Corporation |
11 / 17 page 11 FN6221.0 December 21, 2006 The Full Scale Range, FSR, needs to be determined. From Equation 3: The effective transfer function becomes: Solution 2 - Using External Timing Mode From solution 1, the desired integration time is 100ms. Note that the REXT resistor only determines the inter oscillator frequency when using external timing mode. Instead the integration time is the time between two sync_iic commands sent through the I2C. The programmer determines how many I2C clock cycles to wait between two external timing commands. iI2C = fI2C * Tint = number of I 2C clock cycles iI2C = 10kHz *100ms iI2C = 1,000 I 2C clock cycles. An external sync_iic command sent 1,000 cycles after another sync_iic command rejects both 60Hz and 50Hz AC noise signals. Next is to pick an arbitrary REXT = 100kΩ and to choose the Gain/Range Mode. For a maximum 500Lux, Range1 is adequate. From Equation 3: The effective transfer function becomes: DATA is the sensor reading data located in data registers 04(hex) and 05(hex) COUNTER is the timer counter value data located in data registers 06(hex) and 07(hex). In this sample problem, COUNTER = 1000. Light Source Detection and Infra-Red Rejection Any filament type light source has a high presence of infrared component invisible to the human eye. A white fluorescent lamp, on the other hand has a low IR content. As a result, output sensitivity may vary depending on the light source. Maximum attenuation of IR can be achieved by properly scaling the readings of Diode1 and Diode2. The user obtains data reading from sensor diode 1, D1, which is sensitive to visible and IR, then reading from sensor diode 2, D2 which is mostly sensitive from IR. The graph on Figure 7 shows the effective spectral response after applying Equation 15 of the ISL29003 from 400nm to 1000nm. The equation below describes the method of cancelling IR in internal timing mode. Where: D3 = Lux amount in number of counts less IR presence D1 = data reading of Diode 1 D2 = data reading of Diode 2 n = 1.355. This is a fudge factor to scale back the sensitivity up to ensure Equation 4 is valid. k = 3.355. This is a scaling factor for the IR sensitive Diode 2. Flat Window Lens Design A window lens will surely limit the viewing angle of the ISL29004. The window lens should be placed directly on top of the device. The thickness of the lens should be kept at minimum to minimize loss of power due to reflection and also to minimize loss of loss due to absorption of energy in the plastic material. A thickness of t = 1mm is recommended for a window lens design. The bigger the diameter of the window lens the wider the viewing angle is of the ISL29001. Table 16 shows the recommended dimensions of the optical window to ensure both +35° and +45° viewing angle. These TABLE 14. SOLUTION1 SUMMARY TO EXAMPLE DESIGN PROBLEM DESIGN PARAMETER VALUE Tint 100ms REXT 50k Ω Gain/Range Mode Range1 = 1000Lux FSR 2000Lux # of clock cycles 216 Transfer Function FSR 1000Lux 100k Ω 50k Ω ------------------ = FSR 2000Lux = E data 2 16 ------------- 2000Lux × = E DATA 2 16 ----------------- 2000Lux × = FSR 1000lux 100k Ω 100k Ω ------------------ = FSR 1000Lux = E DATA COUNTER -------------------------------- 1000Lux × = TABLE 15. SOLUTION2 SUMMARY TO EXAMPLE DESIGN PROBLEM DESIGN PARAMETER VALUE Tint 100ms REXT 100k Ω Gain/Range Mode Range1 = 1000Lux FSR 1000Lux # of clock cycles COUNTER = 1000 Transfer Function E DATA COUNTER -------------------------------- 1000Lux × = D3 n D1 kD2 – () = (EQ. 15) ISL29004 |
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