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TMD27711 Datasheet(PDF) 11 Page - TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS |
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TMD27711 Datasheet(HTML) 11 Page - TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS |
11 / 33 page TMD2771 DIGITAL ALS and PROXIMITY MODULE TAOS143B − SEPTEMBER 2012 10 r r Copyright E 2012, TAOS Inc. The LUMENOLOGY r Company www.taosinc.com Proximity Detection Proximity detection is accomplished by measuring the amount of IR energy, from the internal IR LED, reflected off an object to determine its distance. The internal proximity IR LED is driven by the integrated proximity LED current driver as shown in Figure 8. CH1 Prox Integration Prox Control Prox ADC Prox LED Current Driver CH0 PDATAH(r0x019) PDRIVE(r0x0F, b7:6) Prox Data IR LED PTIME(r0x02) PPULSE(r0x0E) PDIODE(r0x0F, b5:4) Background Energy PDATAL(r0x018) Object LDR LEDK LEDA Figure 8. Proximity Detection The LED current driver provides a regulated current sink on the LDR terminal that eliminates the need for an external current limiting resistor. The PDRIVE register setting sets the sink current to 100%, 50%, 25%, or 12.5% of the factory trimmed full scale current. Referring to the Detailed State Machine figure, the LED current driver pulses the IR LED as shown in Figure 9 during the Prox Accum state. Figure 9 also illustrates that the LED On pulse has a fixed width of 7.3 μs and period of 16.0 μs. So, in addition to setting the proximity drive current, 1 to 255 proximity pulses (PPULSE) can be programmed. When deciding on the number of proximity pulses, keep in mind that the signal increases proportionally to PPULSE, while noise increases by the square root of PPULSE. LED On LED Off IR LED Pulses Background Energy Reflected IR LED + Background Energy 16.0 ms 7.3 ms Figure 9. Proximity LED Current Driver Waveform Figure 8 illustrates light rays emitting from the internal IR LED, reflecting off an object, and being absorbed by the CH0 and CH1 photodiodes. The proximity diode selector (PDIODE) determines which of the two photodiodes is used for a given proximity measurement. Note that neither photodiode is selected when the device first powers up, so PDIODE must be set for proximity detection to work. |
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