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ISL29011 数据表(PDF) 10 Page - Intersil Corporation |
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ISL29011 数据表(HTML) 10 Page - Intersil Corporation |
10 / 16 page 10 FN6467.4 May 5, 2011 Registers 06 and 07 hex set the high (HI) threshold for the interrupt pin and the interrupt flag. 06 hex is the LSB and 07 hex is the MSB. By default, the Interrupt threshold HI is FF hex for both LSB and MSB. Test Register (08 hex) Register 8 is a reserved register that holds 00h during normal operation. Calculating Lux The ISL29011’s ADC output codes, DATA, are directly proportional to lux in the ambient light sensing. Here, Ecal is the calculated lux reading. The constant α is determined by the Full Scale Range and the ADC’s maximum output counts. The constant is independent on the light sources (fluorescent, incandescent and sunlight) because of the light sources’ IR component is removed during the light signal process. The constant can also be viewed as the sensitivity: the smallest lux measurement the device can measure as shown in Equation 2. Here, Range(k) is defined in Table 9. Countmax is the maximum output counts from the ADC. The transfer function used for n-bit ADC becomes Equation 3: Here, n = 4, 8, 12 or 16. This is the number of ADC bits programmed in the command register. 2n represents the maximum number of counts possible from the ADC output. Data is the ADC output stored in the data registers (02 hex and 03 hex). Integration and Conversion Time The ADC resolution and fOSC determines the integration time, tint as shown in Equation 4. where n is the number of bits of resolution and n = 4, 8, 12 or 16. 2n, therefore, is the number of clock cycles. n can be programmed at the command register 01(hex) bits 3 and 2. External Scaling Resistor REXT for fOSC and Range The ISL29011 uses an external resistor REXT to fix its internal oscillator frequency, fOSC and the light sensing range, Range. fOSC and Range are inversely proportional to REXT. For user simplicity, the proportionality constant is referenced to 499k Ω as shown in Equations 5 and 6: 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 conversion rate. 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. ADC Output in IR Sensing The ISL29011’s ADC output codes, DATA, are directly proportional to the IR intensity received in the IR sensing. Here, EIR is the received IR intensity. The constant β changes with the spectrum of background IR noise like sunlight and incandescent light. The β also changes with the ADC’s range and resolution selections. ADC Output in Proximity Sensing In the proximity sensing, the ADC output codes, DATA, are directly proportional to the total IR intensity from the background IR noise and from the IR LED driven by the ISL29011. Here, β and EIR have the same meanings as in Equation 7. The constant γ depends on the spectrum of the used IR LED and the ADC’s range and resolution selections. ELED is the IR intensity which is emitted from the IR LED and reflected by a specific objector to the ISL29011. ELED depends on the current to the IR LED and the surface of the object. ELED decreases with the square of the distance between the object and the sensor. If background IR noise is small, EIR can be neglected, and the ADC output directly decreases with the distance. If there is significant background IR noise, ISL29011 offers two schemes to reduce the effect. The first way is do a proximity sensing using Scheme 0, immediately followed by an IR sensing. The differential reading of ADC outputs from the proximity and IR sensing will then reduce the effect of background IR noise and directly decrease with the distance between the object and the sensor. The second way is to do TABLE 11. INTEGRATION TIME OF n-BIT ADC REXT (k Ω) n = 16-BIT (ms) n = 12-BIT (ms) n = 8-BIT (µs) n = 4-BIT (µs) 250 45 2.812 175.5 10.8µs 499** 90 5.63 351 21.6µs **Recommended REXT resistor value Ecal α DATA × = (EQ. 1) α Range k () Countmax ---------------------------- = (EQ. 2) (EQ. 3) Ecal Range k () 2 n --------------------------- DATA × = tint 2 n 1 fOSC -------------- × 2 n REXT 725kHz 499k Ω × ---------------------------------------------- × == (EQ. 4) (EQ. 5) Range 499k Ω REXT ------------------ Range k () × = (EQ. 6) fOSC 499k Ω REXT ------------------ 725 × kHz = DATAIR β E IR × = (EQ. 7) DATAPROX β E IR ×γ E LED × + = (EQ. 8) ISL29011 |
类似零件编号 - ISL29011_11 |
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类似说明 - ISL29011_11 |
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