TSL2672 Datasheet, PDF (11/31 Pages) ams AG – DIGITAL PROXIMITY DETECTOR

TSL2672
DIGITAL PROXIMITY DETECTOR
TAOS133 − MAY 2012
Proximity Detection
Proximity detection is accomplished by measuring the amount of light energy, generally from an IR LED,
reflected off an object to determine its distance. The proximity light source, which is external to the TSL2672
device, is driven by the integrated proximity LED current driver as shown in Figure 10.
PDL(r0x0D,b0)
valid ^Object
V_DD
External IR
LED
PPULSE(r0x0E)
PDRIVE(r0x0F, b7:6)
LDR
Prox LED
Current Driver
PGAIN(r0x0F, b3:2)
POFFSET(r0x1E)
PTIME(r0x02)
PDIODE(r0x0F, b5:4)
Prox Control
Prox
Prox
Integration ADC
Prox
Data
PVALID(r0x13, b1)
PSAT(r0x13, b6)
PDATAH(r0x019)
PDATAL(r0x018)
ill ^CH1
G ^{t Background Energy}
CH0
s _{Figure 10. 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 120 mA, 60 mA, 30 mA, or 15 mA
e _{when PDL is not asserted. However, when PDL is asserted, the drive current is reduced by a factor of about}
m ^{t 8 at VLDR = 1.6 V. To drive an external light source with more than 120 mA or to minimize on-chip ground bounce,}
LDR can be used to drive an external p-type transistor, which in turn drives the light source.
a ⁿ _{Referring to the Detailed State Machine figure, the LED current driver pulses the external IR LED as shown in}
o Figure 11 during the Prox Accum state. Figure 11 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
c _{(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.
l_{Reflected IR LED + Background}
a_{Background Energy Energy}
ic ^{LED On}
LED Off
n ^{7.3 ms}
16.0 ms
ch _{IR LED Pulses}
Te ^{Figure 11. Proximity LED Current Driver Waveform}
Copyright E 2012, TAOS Inc.
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