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ISL29020IROZ-EVALZ 数据表(PDF) 6 Page - Intersil Corporation |
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ISL29020IROZ-EVALZ 数据表(HTML) 6 Page - Intersil Corporation |
6 / 11 page 6 FN6505.1 August 20, 2009 . 5. Range: Bits 1 and 0. The Full Scale Range (FSR) can be adjusted via I2C using Bits 1 and 0. Table 8 lists the possible values of FSR for the 500k Ω R EXT resistor. Data Registers (01 hex and 02 hex) The device has two 8-bit read-only registers to hold a 16-bit data from ADC or Timer. The most significant byte is accessed at 02 hex, and the least significant byte is accessed at 01 hex. The registers are refreshed after every conversion cycle. Calculating Lux The ISL29020’s ADC output codes, DATA, are directly proportional to lux in the ambient light sensing, as shown in Equation 1. 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 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 8. Countmax is the maximum output counts from the ADC. The transfer function used for each timing mode becomes: INTERNAL TIMING MODE 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 in Internal-Timing mode. Data is the ADC output stored in the data registers (01 hex and 02 hex). EXTERNAL TIMING MODE Here, Timer sets up the ADC’s maximum count reading and it is the number of clock cycles accrued in the integration time (set by sync_I2C pulses) in External-Timing mode. It is stored in the data registers 01h and 02h when the command is coded as 1xx101xx. Data is the ADC output. In this mode, the command has to be sent out again with code 1xx100xx to request the ADC output data from registers 01h and 02h. External Scaling Resistor REXT for fOSC and Range The ISL29020 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 500k Ω: 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 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 ISL29020 offers user flexibility in the integration time to balance resolution, speed and noise rejection. Integration time can be set internally or externally by programming the bit 4 of the command register 00(hex). INTEGRATION TIME IN INTERNAL-TIMING MODE Most applications will use the Internal-Timing mode. In this mode, fOSC and ADC n-bits resolution determine the integration time, tint, as shown in Equation 7. 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 00(hex) bits 3 and 2. TABLE 7. RESOLUTION/WIDTH BITS 3:2 NUMBER OF CLOCK CYCLES 0:0 216 = 65,536 0:1 212 = 4,096 1:0 28 = 256 1:1 24 = 16 TABLE 8. RANGE/FSR LUX BITS 1:0 k RANGE(k) FSR (LUX) @ ALS SENSING FSR (LUX) @ IR SENSING 0:0 1 Range1 1,000 Refer to page 2 0:1 2 Range2 4,000 Refer to page 2 1:0 3 Range3 16,000 Refer to page 2 1:1 4 Range4 64,000 Refer to page 2 TABLE 9. DATA REGISTERS ADDRESS (hex) CONTENTS 01 Least-significant byte of most recent ADC or Timer data. 02 Most-significant byte of most recent ADC or Timer data. E cal α DATA × = (EQ. 1) α Range k () Count max ---------------------------- = (EQ. 2) (EQ. 3) E Range k () 2 n --------------------------- DATA × = (EQ. 4) E Range k () Timer --------------------------- DATA × = (EQ. 5) Range 500k Ω R EXT ------------------ Range k () × = (EQ. 6) f OSC 500k Ω R EXT ------------------ 725 × kHz = t int 2 n 1 f OSC -------------- × 2 n R EXT 725kHz 500k Ω × ---------------------------------------------- × == (EQ. 7) ISL29020 |
类似零件编号 - ISL29020IROZ-EVALZ |
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类似说明 - ISL29020IROZ-EVALZ |
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