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TSL25723 Datasheet(PDF) 8 Page - List of Unclassifed Manufacturers |
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TSL25723 Datasheet(HTML) 8 Page - List of Unclassifed Manufacturers |
8 / 24 page TSL2572 LIGHT-TO-DIGITAL CONVERTER TAOS132 − MARCH 2012 8 r r Copyright E 2012, TAOS Inc. The LUMENOLOGY r Company www.taosinc.com ALS Operation The ALS engine contains ALS gain control (AGAIN) and two integrating analog-to-digital converters (ADC), one for the CH0 and one for the CH1 photodiodes. The ALS integration time (ATIME) impacts both the resolution and the sensitivity of the ALS reading. Integration of both channels occurs simultaneously and upon completion of the conversion cycle, the results are transferred to the data registers (C0DATA and C1DATA). This data is also referred to as channel count. The transfers are double-buffered to ensure data integrity. CH1 ADC ALS Control CH1 Data CH0 ALS CH0 Data AGAIN(r0x0F, b1:0) 1 y, 8y, 16y, 120y Gain CH0 CH1 C0DATAH(r0x15), C0DATA(r0x14) C1DATAH(r0x17), C1DATA(r0x16) ATIME(r 1) 2.73 ms to 699 ms AGL(r0x0D, b2) Figure 7. ALS Operation The registers for programming the integration and wait times are 2’s compliment values. The actual time can be calculated as follows: ATIME = 256 − Integration Time / 2.73 ms Inversely, the time can be calculated from the register value as follows: Integration Time = 2.73 ms × (256 − ATIME) In order to reject the 50/60-Hz ripple present in fluorescent lighting, the integration time needs to be programmed in multiples of 10 / 8.3 ms or the half cycle time. Both frequencies can be rejected with a programmed value of 50 ms (ATIME = 0xED) or multiples of 50 ms (i.e. 100, 150, 200, 400, 600). AGAIN can be programmed to 1 ×, 8×, 16×, or 120× with the 2-bit AGAIN field in the Control register (0x0F). The gain, in terms of amount of gain, will be represented by the value AGAINx, i.e. AGAINx = 1, 8, 16, or 120. With the AGL bit set, the 1 × and 8× gains are lowered to 1/6× and 8/6×, respectively, to allow for operation up to 60k lux. Do not enable AGL when AGAIN is 16 × or 120×. Lux Equation The lux calculation is a function of CH0 channel count (C0DATA), CH1 channel count (C1DATA), ALS gain (AGAINx), and ALS integration time in milliseconds (ATIME_ms). If an aperture, glass/plastic, or a light pipe attenuates the light equally across the spectrum (300 nm to 1100 nm), then a scaling factor referred to as glass attenuation (GA) can be used to compensate for attenuation. For a device in open air with no aperture or glass/plastic above the device, GA = 1. If it is not spectrally flat, then a custom lux equation with new coefficients should be generated. (See TAOS application note). Counts per Lux (CPL) needs to be calculated only when ATIME or AGAIN is changed, otherwise it remains a constant. The first segment of the equation (Lux1) covers fluorescent and incandescent light. The second segment (Lux2) covers dimmed incandescent light. The final lux is the maximum of Lux1, Lux2, or 0. CPL = (ATIME_ms × AGAINx) / (GA × 60) Lux1 = (1 × C0DATA − 1.87 × C1DATA) / CPL Lux2 = (0.63 × C0DATA − 1 × C1DATA) / CPL Lux = MAX(Lux1, Lux2, 0) |
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