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ISL29012IROZ-T7 数据表(PDF) 7 Page - Intersil Corporation |
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ISL29012IROZ-T7 数据表(HTML) 7 Page - Intersil Corporation |
7 / 15 page 7 FN6476.1 December 10, 2008 The transfer function effectively for each timing mode becomes: INTERNAL TIMING MODE EXTERNAL TIMING MODE n = 3, 7, 11, or 15. This is the number of clock cycles programmed in the command register. Range(k) is the user defined range in the Gain/Range bit in the command register. REXT is an external scaling resistor hardwired to the REXT pin. DATA is the output sensor reading in number of counts available at the data register. 2n represents the maximum number of counts possible in Internal Timing Mode. For the External Timing Mode the maximum number of counts is stored in the data register named COUNTER. COUNTER is the number increments accrued for between integration time for External Timing Mode. Gain/Range, Range(k) The Gain/Range can be programmed in the control register to give Range(k) determining the FSR. Note that Range(k) is not the FSR (see Equation 3). Range(k) provides four constants depending on programmed k that will be scaled by REXT (see Table 9). Unlike REXT, Range(k) dynamically adjusts the FSR. This function is especially useful when light conditions are varying drastically while maintaining excellent resolution. Number of Clock Cycles, n-bit ADC The number of clock cycles determines “n” in the n-bit ADC; 2n clock cycles is a n-bit ADC. n is programmable in the command register in the width function. Depending on the application, a good balance of speed, and resolution has to be considered when deciding for n. For fast and quick measurement, choose the smallest n = 3. For maximum resolution without regard of time, choose n = 15. Table 12 compares the trade-off between integration time and resolution. See Equations 10 and 11 for the relation between integration time and n. See Equation 3 for the relation of n and resolution. External Scaling Resistor REXT and fOSC The ISL29012 uses an external resistor REXT to fix its internal oscillator frequency, fOSC. Consequently, REXT determines the fOSC, integration time and the FSR of the device. fOSC, a dual speed mode oscillator, is inversely proportional to REXT. For user simplicity, the proportionality constant is referenced to fixed constants 100k Ω and 655kHz in Equations 6 and 7: fOSC1 is oscillator frequency when Range1 or Range2 are set. This is nominally 342kHz when REXT is 100kΩ. fOSC2 is the oscillator frequency when Range3 or Range4 are set. This is nominally 684kHz when REXT is 100kΩ. When the Range/Gain bits are set to Range1 or Range2, fOSC runs at half speed compared to when Range/Gain bits are set to Range3 and Range4 by using Equation 8: The automatic fOSC adjustment feature allows significant improvement of signal-to-noise ratio when detecting very low lux signals. Integration Time or Conversion Time Integration time is the period during which the device’s analog-to-digital ADC converter samples the photodiode current signal for a lux measurement. Integration time, in other words, is the time to complete the conversion of analog photodiode current into a digital signal--number of counts. Integration time affects the measurement resolution. For better resolution, use a longer integration time. For short and fast conversions, use a shorter integration time. The ISL29012 offers user flexibility in the integration time to balance resolution, speed and noise rejection. Integration time can be set internally or externally and can be programmed in the command register 00(hex) Bit 5. (EQ. 4) E Range k () 100kΩ R EXT ------------------ × 2 n ---------------------------------------------------- DATA × = (EQ. 5) E Range k () 100kΩ R EXT ------------------ × COUNTER ---------------------------------------------------- DATA × = TABLE 12. RESOLUTION AND INTEGRATION TIME SELECTION n RANGE1 fOSC = 327kHz RANGE4 fOSC = 655kHz tINT (ms) RESOLUTION LUX/COUNT tINT (ms) RESOLUTION (LUX/COUNT) 15 200 0.06 100 2 11 12.8 1.0 6.4 62.5 7 0.8 15.6 0.4 1,000 3 0.05 250 0.025 16,000 REXT = 100kΩ (EQ. 6) f OSC1 1 2 --- 100k Ω R EXT ------------------ 684 × kHz × = (EQ. 7) f OSC2 100k Ω R EXT ------------------ 684 × kHz = (EQ. 8) f OSC1 1 2 --- f OSC2 () = ISL29012 |
类似零件编号 - ISL29012IROZ-T7 |
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类似说明 - ISL29012IROZ-T7 |
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