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ISL29012 数据表(PDF) 8 Page - Intersil Corporation |
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ISL29012 数据表(HTML) 8 Page - Intersil Corporation |
8 / 15 page 8 FN6476.1 December 10, 2008 Integration time in Internal Timing Mode This timing mode is programmed in the command register 00(hex) Bit 5. Most applications will be using this timing mode. When using the Internal Timing Mode, fOSC and n-bits resolution determine the integration time. tINT is a function of the number of clock cycles and fOSC as shown in Equation 9: m = 4, 8, 12, and16. n is the number of bits of resolution. 2m therefore is the number of clock cycles. n can be programmed at the command register 00(hex) Bits 1 and 0. Since fOSC is dual speed depending on the Gain/Range bit, tINT is dual time. The integration time as a function of REXT is shown in Equation 10: tINT1 is the integration time when the device is configured for Internal Timing Mode and Gain/Range is set to Range1 or Range2. tINT 2 is the integration time when the device is configured for Internal Timing Mode and Gain/Range is set to Range3 or Range4. Integration time in External Timing Mode This timing mode is programmed in the command register 00(hex) Bit 5. External Timing Mode is recommended when integration time can be synchronized to an external signal such as a PWM to eliminate noise. To read the light count DATA output, the device needs three sync_I2C commands to complete one measurement. The 1st sync_I2C command starts the conversion of the diode array 1. The 2nd sync_I2C completes the conversion of diode array 1 and starts the conversion of diode array 2. The 3rd sync_I2C pules ends the conversion of diode array 2, outputs the light count DATA, and starts over again to commence conversion of diode array 1. The integration time, tINT, is the sum of two identical time intervals between the three sync pulses. tINT is determined by Equation 12: where KOSC is the number of internal clock cycles obtained from Timer data register and fOSC is the internal I 2C operating frequency The internal oscillator, fOSC, operates identically in both the internal and external timing modes, with the same dependence on REXT. However, in External Timing Mode, the number of clock cycles per integration is no longer fixed at 2n. The number of clock cycles varies with the chosen integration time, and is limited to 216 = 65,536. In order to avoid erroneous lux readings, the integration time must be short enough not to allow an overflow in the counter register. fOSC = 342kHz*100kΩ/REXT. When Range/Gain is set to Range1 or Range2. fosc = 684kHz*100kΩ/REXT. When Range/Gain is set to Range3 or Range4. Noise Rejection In general, integrating type ADC’s have excellent noise-rejection characteristics for periodic noise sources whose frequency is an integer multiple of the integration time. For instance, a 60Hz AC unwanted signal’s sum from 0ms to k*16.66ms (k = 1,2...ki) is zero. Similarly, setting the device’s integration time to be an integer multiple of the periodic noise signal, greatly improves the light sensor output signal in the presence of noise. Ambient Light Sensing Operation The operation of ambient light sensing (ALS) within the ISL29012 utilizes two diodes; D1 and D2. The D1 diode is sensitive to both visible and IR light spectrum. The D2 diode is sensitive to IR spectrum. D1 and D2 spectrum response is shown in Figure 21. The diodes are measured sequentially and their outputs are converted with an ADC. The output of the ALS is the difference between these two measurements. Maximum Ambient Intensity Condition In typical applications, the ISL29012 is installed behind a dark cover window. In this low-light condition, both D1 and D2 operate linearly and the ALS output is linear as well (Figures 19 and 20). In brighter environments and with transparent glass, however, D1 and D2 can be subject to saturation. As the ambient light grows bright enough to subject one or both diodes to saturation, the ALS count (output) decreases and eventually reaches zero in deep TABLE 13. INTEGRATION TIMES FOR TYPICAL REXT VALUES REXT (k Ω) RANGE1 RANGE2 RANGE3 RANGE4 n = 15-BIT n = 11-BIT n = 11-BIT n = 3 50 100 6.4 3.2 0.013 100** 200 13 6.5 0.025 200 400 26 13 0.050 500 1000 64 32 0.125 *Integration time in milliseconds **Recommended REXT resistor value t INT 2 m 1 f osc ---------- × = (EQ. 9) for Internal Timing Mode only t INT12 m R EXT 342kHz 100k Ω × ---------------------------------------------- × = (EQ. 10) t INT22 m R EXT 684kHz 100k Ω × ---------------------------------------------- × = (EQ. 11) t INT k OSC f OSC --------------- = (EQ. 12) t INT 65,535 f OSC ------------------ < (EQ. 13) ISL29012 |
类似零件编号 - ISL29012 |
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类似说明 - ISL29012 |
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