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ISL29043IROMZ-T7 Folha de dados(PDF) 10 Page - Intersil Corporation |
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ISL29043IROMZ-T7 Folha de dados(HTML) 10 Page - Intersil Corporation |
10 / 16 page ISL29043 10 FN7935.0 February 9, 2012 Ambient Light and IR Sensing The ISL29043 is set for ambient light sensing when Register bit ALSIR_MODE = 0 and ALS_EN = 1. The light-wavelength response of the ALS appears as shown in Figure 11. ALS measuring mode (as opposed to IR measuring mode) is set by default. When the part is programmed for infrared (IR) sensing (ALSIR_MODE = 1; ALS_EN = 1), infrared light is converted into a current and digitized by the same ALS ADC. The result of an IR conversion is strongly related to the amount of IR energy incident on our sensor, but is unitless and is referred to in digital counts. Proximity Sensing When proximity sensing is enabled (PROX_EN = 1), the internal IR LED is driven for 0.1ms by the built-in IR LED driver through the IRDR pin. The amplitude of the IR LED current depends on Register 1 bit 3: PROX_DR. If this bit is low, the load will see a fixed 110mA current pulse. If this bit is high, the load on IRDR will see a fixed 220mA current pulse, as seen in Figure 6. When the IR from the LED reaches an object and gets reflected back into the ISL29043, the reflected IR light is converted into current as per the IR spectral response shown in Figure 11. One entire proximity measurement takes 0.54ms for one conversion (which includes 0.1ms spent driving the LED), and the period between proximity measurements is decided by PROX_SLP (sleep time) in Register 1 Bits 6:4. Average LED driving current consumption is given by Equation 1. A typical IRDR scheme is 220mA amplitude pulses every 800ms, which yields 28μA DC. Total Current Consumption Total current consumption is the sum of IDD and IIRDR. The IRDR pin sinks current (as shown in Figure 6) and the average IRDR current can be calculated using Equation 1. IDD depends on voltage and the mode-of-operation, as seen in Figure 15. Interrupt Function The ISL29043 has an intelligent interrupt scheme designed to shift some logic processing away from intensive microcontroller I2C polling routines (which consume power) and towards a more independent light sensor, which can instruct a system to “wake up” or “go to sleep”. 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 ISL29043 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 re-measure 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. For more information, please contact the factory. 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 ISL29043 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 ISL29043’s ADC output codes are directly proportional to lux when in ALS mode (see ALSIR_MODE bit). FIGURE 6. CURRENT DRIVE MODE OPTIONS IRDR 220mA (PROX_DR = 1) (IRDR IS HI-Z WHEN NOT DRIVING) 110mA (PROX_DR = 0) LED+ INTERNAL IR-LED LED- PCB TRACE IlRDR AVE ; IlRDR PEAK ; 100 μs × TSLEEP -------------------------------------------------------- = (EQ. 1) Ecalc α RANGE OUTADC × = (EQ. 2) |
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