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ISL29021IROZ-T7 数据表(PDF) 8 Page - Intersil Corporation |
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ISL29021IROZ-T7 数据表(HTML) 8 Page - Intersil Corporation |
8 / 12 page 8 FN6732.0 March 3, 2009 background IR noise and from the IR LED driven by the ISL29021 as shown in Equation 5. Here, β and EIR have the same meanings as in Equation 4. The constant γ depends on the spectrum of the used IR LED and the ADC’s range and resolution selections. ELED is the IR intensity which is emitted from the IR LED and reflected by a specific objector to the ISL29021. ELED depends on the current to the IR LED and the surface of the object. ELED decreases with the square of the distance between the object and the sensor. If background IR noise is small, EIR can be neglected, and the ADC output directly decreases with the distance. If there is significant background IR noise, ISL29021 is to do a proximity sensing using Scheme 1 to do on-chip background IR noise subtraction. Figure 9 shows ISL29021 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 10 shows ISL29021 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. ISL29021 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, ISL29021 is sensitive enough to detect a black ESD foam, which reflects slightly less than 1% of IR, as shown in Figure 9. For biological objects, blonde hair reflects more than brunette hair, as expected and shown in Figure 11. 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 infrared signal 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. LED Modulation for Proximity Detection ISL29021 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 2x more current. The sensitivity of LED 50mA, DC 50mA is identical to that of 100mA, 360kHz modulation. Please note that the ISL29021 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 3, the device requires three different phases in serial during the entire detection cycle to do 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 3 also shows the current consumption during each 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 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 6: 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 7: 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 ISL29021 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 1µF and 0.1µF, placed close to the device. DATAPROX β E IR ×γ E LED × + = (EQ. 5) 0.05mA 0.05mA 1mA (50mA∗50%))∗0.4ms ++ + () []/30ms = 0.35mA (EQ. 6) 0.05mA 0.05mA 1mA (50mA∗50%))∗ 7ms ++ + () []/100ms = 1.83mA (EQ. 7) ISL29021 |
类似零件编号 - ISL29021IROZ-T7 |
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类似说明 - ISL29021IROZ-T7 |
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