TSL2671

DIGITAL PROXIMITY DETECTOR

TAOS118 − JANUARY 2011

8

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Copyright

E 2011, TAOS Inc.

The LUMENOLOGY

r Company

www.taosinc.com

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 6). The amount of light detected from a reflected surface can then be used to determine an object’s

proximity to the sensor.

IR LED

2771

Surface Reflectivity (SR)

Background Energy (BGE)

Optical Crosstalk (OC)

Glass Attenuation (GA)

Distance (D)

Figure 6. Proximity Detection

The device has controls for the number of IR pulses (PPCOUNT), the integration time (PTIME), the LED drive

current (PDRIVE), and the photodiode configuration (PDIODE) (Figure 7). The photodiode configuration can

be set to CH1 diode (recommended), CH0 diode, or a combination of both diodes. At the end of the integration

cycle, the results are latched into the proximity data (PDATAx) registers.

CH1

Prox

Integration

Prox Control

Prox

ADC

IR LED Constant

Current Sink

CH0

PDATAH(r0x19), PDATAL(r0x18)

PDRIVE(r0x0F, b7:6)

Prox

Data

IR

LED

PTIME(r0x02)

PPCOUNT(r0x0E)

Figure 7. Proximity Detection Operation

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 type transistor can be used to

control the LED current.