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ISL29038IROZ-T7 参数 Datasheet PDF下载

ISL29038IROZ-T7图片预览
型号: ISL29038IROZ-T7
PDF下载: 下载PDF文件 查看货源
内容描述: [Low Power Ambient Light and Proximity Sensor with Enhanced Infrared Rejection]
分类和应用: 光电二极管
文件页数/大小: 15 页 / 560 K
品牌: XICOR [ XICOR INC. ]
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ISL29038  
ALS IR Compensation  
Proximity Ambient Washout Detection  
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.  
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.  
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.  
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_IR_COMP register (Reg 0x03[4:0]) allows fine tuning of  
the residual infrared component from the ALS output.  
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].  
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.  
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].  
• 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.  
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.  
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).  
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].  
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.  
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.  
GLASS COVER  
Power-Up and ‘Brown-Out’ Reset  
SENSOR  
LED  
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.  
PCB  
FIGURE 11. PROXIMITY SET-UP HIGHLIGHTING CROSSTALK  
REFLECTED FROM COVER GLASS  
A ‘Brown-Out’ condition is defined as an operating condition  
when the power supply voltage is not within the specified limits.  
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.  
2
During the brown-out period at power-up, the I C interface and  
2
the IR LED driver are inactive. Following brown-out, the I C  
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  
FN7851.0  
October 12, 2012  
11