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ISL29038IROZ-EVALZ 데이터시트(PDF) 11 Page - Xicor Inc. |
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ISL29038IROZ-EVALZ 데이터시트(HTML) 11 Page - Xicor Inc. |
11 / 15 page ISL29038 11 FN7851.0 October 12, 2012 ALS IR Compensation The ISL29038 is designed for operation under dark glass cover. Glass or plastic covers can significantly attenuate visible light and pass the Infrared light without much attenuation. Consequently, the ISL29038 under a glass cover experiences an IR rich environment. The on-chip ALS passive optical filter on the ISL29038 is designed to block most of the IR incident on the ALS photo diodes. In addition, the ISL29038 provides a programmable active IR compensation that subtracts residual IR still reaching the sensor. The ALS_IR_COMP register (Reg 0x03[4:0]) allows fine tuning of the residual infrared component from the ALS output. The recommended procedure for determining ALS IR compensation is as follows: • Illuminate the ISL29038 based product with a light source without IR, such as a white LED. Record the ALS measurement and the Lux level. • Illuminate the device with an IR LED and the White LED. Take an ALS measurement and Lux level measurement. • Adjust the ALS_IR_COMP register (Reg 0x03, bits 4:0) to compensate for the IR contribution. • Repeat steps above until the IR light source contribution to the ALS measurement is under 10 percent assuming no change in Lux level due to IR light source. Proximity Offset Systems built with a protective glass cover over the ISL29038 can provide light ‘leakage’ or ‘crosstalk’ from the IR LED by reflection from the glass saturating the proximity sensor measurement system (Figure 11). Saturation can occur when the reflection from the glass with no object in the proximity detection space exceeds the full scale of the measurement system. The ISL29038 proximity system provides a user programmable proximity offset correction to compensate for this reflection. The PROX_IR_COMP register (Reg 0x02[6:3]) applies a corrective offset to the received signal prior to ADC conversion, which allows the signal to be brought within the usable range of the proximity measurement system. Proximity Ambient Washout Detection Optical proximity sensor can saturate when illuminated with excessive ambient light. The ISL29038 provides a warning flag when the proximity measurement may be erroneous due to excessive ambient light. The PROX_WASH register (Reg 0x0D[0]) reports this condition. Interrupts Events The ISL29038 interrupts are designed to minimize host micro-controller overhead of continuous polling. ISL29038 can generate interrupts on the results of an ALS measurement or proximity measurement. The ALS interrupt event ALS_FLAG (Reg 0x04[3]) is governed by Reg 0x07 through 0x09. Two-12 bit high and low threshold values are written to these registers. The ISL29038 will set the ALS interrupt flag if the ADC conversion count in Registers 0x0B and 0x0C are outside the programmed thresholds. The ALS_FLAG is cleared by writing a ‘0’ to Reg 0x04[3]. A proximity interrupt event (PROX_FLAG) is governed by the high and low thresholds in Reg 0x05 and 0x06 (PROX_LT and PROX_HT) and is indicated by Reg 0x04[7]. PROX_FLAG is set when the measured proximity data is more than the higher threshold. The proximity interrupt flag is cleared when the proximity data is lower than the low proximity threshold or by writing a ‘0’ to Reg 0x04[7]. The Proximity interrupt generation can be selected between ‘out-of-window’ threshold and hysteresis schemes. When the PROX_INT_ALG register (Reg 0x02, Bit 7) is set to 0, proximity uses a window comparator scheme; when set to 1, proximity uses a hysteresis scheme. In hysteresis mode, the interrupt event is generated if the proximity ADC count is higher than the PROX_HT threshold and the interrupt event is cleared when the proximity ADC count is less than the PROX_LT threshold. The interrupt event flag can also be cleared by writing a ‘0’ to Reg 0x04[7]. INTERRUPT PERSISTENCE To minimize interrupt events due to ‘transient’ conditions, an interrupt persistency option is available for both ALS and proximity measurements. Persistency requires ‘X-consecutive’ interrupt flags before the INT pin is driven low. Both ALS and PROX have their own independent interrupt persistency options. ALS_PRST and PROX_PRST configuration are controlled from Reg 0x04. Power-Up and ‘Brown-Out’ Reset The ISL29038 has an enhanced power-on-reset system. A ‘Brown-Out’ detector flag in Reg 0x04[4] informs the system that the device has powered-up properly. This flag should be reset as part of the initialization sequence. A ‘Brown-Out’ condition is defined as an operating condition when the power supply voltage is not within the specified limits. During the brown-out period at power-up, the I2C interface and the IR LED driver are inactive. Following brown-out, the I2C interface is re-initialized and the configuration registers are set to power-up default values. After power-up and during device initialization, host should examine that the PWR_FAIL flag (Reg FIGURE 11. PROXIMITY SET-UP HIGHLIGHTING CROSSTALK REFLECTED FROM COVER GLASS LED SENSOR PCB GLASS COVER |
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