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ISL29033 Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL29033 Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 15 page ISL29033 9 FN7656.5 September 28, 2016 Submit Document Feedback Command Register II 01 (Hex) The second command register has the following functions: 1. Resolution: Bits 3 and 2. Bits 3 and 2 determine the ADC resolution and the number of clock cycles per conversion (Table 5). Changing the number of clock cycles does more than just change the resolution of the device; it also changes the integration time, which is the period during which the Analog-to-Digital (A/D) converter samples the photodiode current signal for a measurement. 2. Range: Bits 1 and 0. The Full Scale Range (FSR) can be adjusted through the I2C by using Bits 1 and 0. Table 6 lists the possible values of FSR for the 499kΩ REXT resistor. Data Registers (02 Hex and 03 Hex) The device has two 8-bit read-only registers to hold the data from LSB to MSB for the ADC (Table 7). The Most Significant Bit (MSB) is accessed at 03 hex and the Least Significant Bit (LSB) is accessed at 02 hex. For 16-bit resolution, the data is from D0 to D15; for 12-bit resolution, the data is from D0 to D11; for 8-bit resolution, the data is from D0 to D7. The registers are refreshed after every conversion cycle. Interrupt Registers (04, 05, 06, and 07 Hex) Registers 04 and 05 hex set the Low (LO) threshold for the interrupt pin and the interrupt flag. Register 04 hex is the LSB and Register 05 hex is the MSB. By default, the interrupt threshold LO is 00 hex for both LSB and MSB. Registers 06 and 07 hex set the High (HI) threshold for the interrupt pin and the interrupt flag. Register 06 hex is the LSB and Register 07 hex is the MSB. By default, the interrupt threshold HI is FF hex for both LSB and MSB. Calculating Lux The ISL29033 ADC output codes, DATA, are directly proportional to lux in ambient light sensing, as shown in Equation 1. In this equation, Ecal is the calculated lux reading. The constant, α, is determined by the full scale range and the ADC maximum output counts. The constant is independent of the light sources (fluorescent, incandescent, and sunlight) because the light source 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. In this equation, Range(k) is as defined in Table 6. Countmax is the maximum output counts from the ADC. The transfer function used for n-bits ADC is as shown in Equation 3: In this equation, n = 4, 8, 12 or 16 and is the number of ADC bits programmed in the command register. The number 2n represents the maximum number of counts possible from the ADC output. Data is the ADC output stored in data Registers 02 hex and 03 hex. Integration and Conversion Time ADC resolution and fOSC determine the integration time, tint, as shown in Equation 4. In this equation, n is the number of bits of resolution and n = 4, 8, 12 or 16. Therefore, 2n is the number of clock cycles. The value of n can be programmed at the command register, Register 01 hex, Bits 3 and 2 see (Table 8). TABLE 4. INTERRUPT PERSIST BIT 1:0 NUMBER OF INTEGRATION CYCLES 00 1 01 4 10 8 11 16 TABLE 5. ADC RESOLUTION DATA WIDTH BITS 3:2 NUMBER OF CLOCK CYCLES n-BIT ADC 00 216 = 65,536 16 01 212 = 4,096 12 10 28 = 256 8 11 24 = 16 4 TABLE 6. RANGE/FSR LUX BITS 1:0 k RANGE(k) FSR (lux) AT ALS SENSING 00 1 Range1 125 01 2 Range2 500 10 3 Range3 2,000 11 4 Range4 8,000 TABLE 7. DATA REGISTERS ADDRESS (HEX) CONTENTS 02 D0 is LSB for 4-, 8-, 12- or 16-bit resolution; D3 is MSB for 4-bit resolution; D7 is MSB for 8-bit resolution 03 D15 is MSB for 16-bit resolution; D11 is MSB for 12-bit resolution TABLE 8. INTEGRATION TIME OF n-BIT ADC REXT (kΩ) n = 16-BIT (ms) n = 12-BIT (ms) n = 8-BIT (µs) n = 4-BIT (µs) 499 100 6.25 391 24 1000 200 12.5 782 48 Ecal DATA = (EQ. 1) Range k Countmax ---------------------------- = (EQ. 2) (EQ. 3) Ecal Range k 2 n --------------------------- DATA = tint 2 n 1 fOSC -------------- 2 n REXT 655kHz 499k ---------------------------------------------- == (EQ. 4) |
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