TCS3771 Datasheet, PDF (12/33 Pages) ams AG – COLOR LIGHT-TO-DIGITAL CONVERTER with PROXIMITY SENSING

TCS3771
COLOR LIGHT-TO-DIGITAL CONVERTER
with PROXIMITY SENSING
TAOS110A − MARCH 2011
Proximity Detection
Proximity sensing uses an external light source (generally an infrared emitter) to emit light, which is then viewed
by the integrated light detector to measure the amount of reflected light when an object is in the light path
(Figure 9). The amount of light detected from a reflected surface can then be used to determine an object’s
proximity to the sensor.
Surface Reflectivity (SR)
Glass Attenuation (GA)
Distance (D)
IR LED
alid ³⁷⁷¹
v _{Background Energy (BGE)}
Optical Crosstalk (OC)
ill ^{Figure 9. Proximity Detection}
t _{The TCS3771 has controls for the number of IR pulses (PPCOUNT), the integration time (PTIME), the LED drive}
current (PDRIVE) and the photodiode configuration (PDIODE). The photodiode configuration can be set to red
G _{s diode (recommended), clear diode, or a combination of both diodes. At the end of the integration cycle, the}
results are latched into the proximity data (PDATA) register.
A ^t _{IR VDD}
ams ^{nten LED}
PDRIVE(r 0x0F, b7:6)
PTIME(r 2)
IR LED Constant
Current Sink
Prox Control
Prox
Prox
Integration ADC
Prox
Data
PDATAH(r 0x01C)
co _Clear
Red
PPCOUNT(r 0x0E)
al_{Figure 10. Proximity Detection Operation}
ic ^{The LED drive current is controlled by a regulated current sink on the LDR pin. This feature eliminates the need}
to use a current limiting resistor to control LED current. The LED drive current can be configured for 12.5 mA,
25 mA, 50 mA, or 100 mA. For higher LED drive requirements, an external P-FET transistor can be used to
n _{control the LED current.}
h The number of LED pulses can be programmed to any value between 1 and 255 pulses as needed.
Increasing the number of LED pulses at a given current will increase the sensor sensitivity. Sensitivity grows
Tec ^{by the square root of the number of pulses. Each pulse has a 14-μs period.}
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Copyright E 2011, TAOS Inc.
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