TMD27721 Datasheet, PDF (12/35 Pages) TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS – DIGITAL ALS and PROXIMITY MODULE

TMD2772
DIGITAL ALS
and PROXIMITY MODULE
TAOS147E − DECEMBER 2012
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.
LEDA
IR
PDL(r0x0D,b0)
valid ^Object
LEDK
LDR
LED ^{PPULSE(r0x0E)}
PDRIVE(r0x0F, b7:6)
Prox LED
Current Driver
PGAIN(r0x0F, b3:2)
POFFSET(r0x1E)
PTIME(r0x02)
Prox Control
PVALID(r0x13, b1)
PSAT(r0x13, b6)
PDIODE(r0x0F, b5:4)
Prox
Prox
Integration ADC
Prox
Data
PDATAH(r0x019)
PDATAL(r0x018)
ill ^CH1
G ^{t Background Energy}
CH0
s _{Figure 8. Proximity Detection}
A ^t _{The LED current driver, output on the LDR terminal, provides a regulated current sink that eliminates the need}
s ^{n for an external current limiting resistor. The combination of proximity LED drive strength (PDRIVE) and proximity}
drive level (PDL) determine the drive current. PDRIVE sets the drive current to 116 mA, 58 mA, 29 mA, or
e _{14.5 mA when PDL is not asserted. However, when PDL is asserted, the drive current is reduced by a factor}
m ^{t of 9.}
a ^{n 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
o 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
c _{proportionally to PPULSE, while noise increases by the square root of PPULSE.}
l_{Reflected IR LED + Background}
Background Energy Energy
a _{LED On}
LED Off
ic _{7.3 ms}
16.0 ms
chn ^{IR LED Pulses}
Te ^{Figure 9. Proximity LED Current Driver Waveform}
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r
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Copyright E 2012, TAOS Inc.
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