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ISL29028AIROZ-T7 Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL29028AIROZ-T7 Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 16 page ISL29028A 10 FN7721.2 March 24, 2011 An ALS interrupt event (ALS_FLAG) is governed by Registers 5 through 7. The user writes a high and low threshold value to these registers and the ISL29028A will issue an ALS interrupt flag if the actual count stored in Registers 0x9 and 0xA are outside the user’s programmed window. The user must write 0 to clear the ALS_FLAG. A proximity interrupt event (PROX_FLAG) is governed by the high and low thresholds in registers 3 and 4 (PROX_LT and PROX_HT). PROX_FLAG is set when the measured proximity data is more than the higher threshold X-times-in-a-row (X is set by user; see next paragraph). The proximity interrupt flag is cleared when the prox data is lower than the low proximity threshold X-times-in-a-row, or when the user writes “0” to PROX_FLAG. Interrupt persistency is another useful option available for both ALS and proximity measurements. Persistency requires X-in-a- row interrupt flags before the INT pin is driven low. Both ALS and Prox have their own independent interrupt persistency options. See ALS_PRST and PROX_PRST bits in Register 2. The final interrupt option is the ability to AND or OR the two interrupt flags using Register 2 Bit 0 (INT_CTRL). If the user wants both ALS/Prox interrupts to happen at the same time before changing the state of the interrupt pin, set this bit high. If the user wants the interrupt pin to change state when either the ALS or the Proximity interrupt flag goes high, leave this bit to its default of 0. ALS Range 1 Considerations When measuring ALS counts higher than 1800 on range 1 (ALSIR_MODE = 0, ALS_RANGE = 0, ALS_DATA > 1800), switch to range 2 (change the ALS_RANGE bit from “0” to “1”) and remeasure ALS counts. This recommendation pertains only to applications where the light incident upon the sensor is IR-heavy and is distorted by tinted glass that increases the ratio of infrared to visible light. VDD Power-up and Power Supply Considerations Upon power-up, please ensure a VDD slew rate of 0.5V/ms or greater. After power-up, or if the user’s power supply temporarily deviates from our specification (2.25V to 3.63V), Intersil recommends the user write the following: write 0x00 to register 0x01, write 0x29 to register 0x0F, write 0x00 to register 0x0E, and write 0x00 to register 0x0F. The user should then wait ~1ms or more and then rewrite all registers to the desired values. If the user prefers a hardware reset method instead of writing to test registers: set VDD =0V for 1 second or more, power back up at the required slew rate, and write registers to the desired values. Power-Down To put the ISL29028A into a power-down state, the user can set both PROX_EN and ALS_EN bits to 0 in Register 1. Or more simply, set all of Register 1 to 0x00. Calculating Lux The ISL29028A’s ADC output codes are directly proportional to lux when in ALS mode (see ALSIR_MODE bit). In Equation 2, Ecalc is the calculated lux reading and OUT represents the ADC code. The constant α to plug in is determined by the range bit ALS_RANGE (register 0x1 bit 1) and is independent of the light source type. Table 15 shows two different scale factors: one for the low range (ALS_RANGE = 0) and the other for the high range (ALS_RANGE = 1). Noise Rejection Charge balancing 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. Since wall sockets may output at 60Hz or 50Hz, our integration time is 100ms: the lowest common integer number of cycles for both frequencies. Proximity Detection of Various Objects Proximity sensing relies on the amount of IR reflected back from objects. A perfectly black object would absorb all light and reflect no photons. The ISL29028A is sensitive enough to detect black ESD foam which reflects only 1% of IR. For biological objects, blonde hair reflects more than brown hair and customers may notice that skin tissue is much more reflective than hair. IR penetrates into the skin and is reflected or scattered back from within. As a result, the proximity count peaks at contact and monotonically decreases as skin moves away. The reflective characteristics of skin are very different from that of paper. TABLE 15. ALS SENSITIVITY AT DIFFERENT RANGES ALS_RANGE αRANGE (Lux/Count) 0 0.0326 1 0.522 Ecalc α RANGE OUTADC × = (EQ. 2) |
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