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ISL29011 Datasheet(PDF) 11 Page - Intersil Corporation |
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ISL29011 Datasheet(HTML) 11 Page - Intersil Corporation |
11 / 16 page 11 FN6467.3 February 4, 2010 a proximity sensing using Scheme 1 to do on-chip background IR noise subtraction. While Scheme 0 has wider dynamic range, Scheme 1 proximity detection is faster but with half the resolution. Please refer to “Typical Performance Curves” on page 13 for ADC output versus distance using Scheme 0 detection. Figure 10 shows ISL29011 configured at 12-bit ADC resolution and sensitivity range select at 16000 (range 3) for the proximity reading. A 12.5mA external LED current at 360kHz modulation frequency detects three different sensing objects: 92% brightness paper, 18% gray card and ESD black foam. Figure 11 shows ISL29011 configured at 12-bit ADC resolution and sensitivity range select at 1000 (range 1) for the proximity reading, with a programmed external LED at 360kHz modulation frequency, detecting the same sensing object: 18% gray card under four different external LED current: 12.5mA, 25mA, 50mA and 100mA to compare the proximity readout versus distance. ISL29011 Proximity sensing relies on the amount of IR reflected back from the objects to be detected. Clearly, it can not detect an optically black object that reflects no light. However, ISL29011 is sensitive enough to detect a black ESD foam, which reflects slightly less than 1% of IR, as shown in Figure 10 on page 13. For biological objects, blonde hair reflects more than brunette hair, as expected and shown in Figure 12. Also 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. This characteristic is very different from that of a plain paper reflector. Interrupt Function Depending on the mode of operation set by Bits 7, 6 and 5 of command register 00 hex, the upper and lower interrupt thresholds are for either ambient light level or proximity detection. After each change of mode of operation, it is expected a new set of thresholds are loaded to interrupt registers 04, 05, 06 and 07 hex for proper interrupt detection. Also, the interrupt persist counter will be reset to 0 when the mode of operation is changed. 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 0x00 to two registers: 0x08, 0x00 (in that order), wait ~1ms or more and then rewrite all registers as desired. LED Modulation for Proximity Detection ISL29011 offers two ways to modulate the LED in the Proximity Detection mode - DC or 360kHz (with 50% duty cycle) by bit 6 of register 01h. At the IRDR pin, there are four different IRDR LED currents; 12.5, 25, 50, and 100mA outputs selectable by bits 4 and 5 of register 01h. With the LED running in the DC mode, the proximity detection is twice as sensitive but consumes 2 times more current. The sensitivity of LED 50mA, DC 50mA is identical to that of 100mA, 360kHz modulation. Please note that the ISL29011 does not include a LED. Current Consumption Estimation The low power operation is achieved through sequential readout in the serial fashion, as shown in Figure 4, the device requires three different phases in serial during the entire detection cycle to do ambient light sensing, infrared sensing and proximity sensing. The external IR LED will only be turned on during the proximity sensing phase under user program controlled current at modulated frequency depends on user selections. Figure 4 also shows the current consumption during each ALS, IR sensing and Proximity sensing phase. For example, at 8-bit ADC resolution the integration time is 0.4ms. If user programed 50mA current to supply external IR LED at 360kHz modulated frequency, during the entire operation cycle that includes ALS, IR sensing and Proximity sensing three different serial phases, the detection occurs once every 30ms, the average current consumption including external IR LED drive current can be calculated from Equation 9: If at a 12-bit ADC resolution where the integration time for each serial phase becomes 7ms and the total detection time becomes 100ms, the average current can be calculated from Equation 10: Suggested PCB Footprint It is important that the users check the “Surface Mount Assembly Guidelines for Optical Dual FlatPack No Lead (ODFN) Package” before starting ODFN product board mounting. http://www.intersil.com/data/tb/TB477.pdf Layout Considerations The ISL29011 is relatively insensitive to layout. Like other I2C devices, it is intended to provide excellent performance even in significantly noisy environments. There are only a few considerations that will ensure best performance. Route the supply and I2C traces as far as possible from all sources of noise. Use two power-supply decoupling capacitors 1uF and 0.1µF and place them close to the VDDA and VDDD pins of the device. Typical Circuit A typical application for the ISL29011 is shown in Figure 5. The ISL29011’s I2C address is internally hardwired as 0.05mA 0.05mA 1mA (50mA∗50%))∗0.4ms ++ + () []/30ms = 0.35mA (EQ. 9) 0.05mA 0.05mA 1mA (50mA∗50%))∗ 7ms ++ + () []/100ms = 1.83mA (EQ. 10) ISL29011 |
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