TCS37727FN datasheet(19/51 Pages) OSRAM

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[v1-01] 2018-Mar-14

TCS3772 − Principles of Operation

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 TCS3772 device, is driven by the integrated

proximity LED current driver.

Figure 24:

Proximity Detection

The LED current driver, output on the LDR terminal, provides a

regulated current sink that eliminates the need for an external

current limiting resistor. PDRIVE sets the drive current to

100 mA, 50 mA, 25 mA. To drive an external light source with

more than 100 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.

Referring to the Detailed State Machine figure, the LED

current driver pulses the external IR LED as shown in Figure 25

during the Prox Accum state. Figure 25 also illustrates that the

LED On pulse has a fixed width of 6.3

μs and period of 14.0 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.

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