TCS3772 datasheet(20/51 Pages) OSRAM

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ams Datasheet

Page 19

[v1-01] 2018-Mar-14

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TCS3772 − Principles of Operation

Figure 25:

Proximity LED Current Driver Waveform

Figure 24 illustrates light rays emitting from an external IR LED,

reflecting off an object, and being absorbed by the proximity

photodiode.

Referring again to Figure 25, the reflected IR LED and the

background energy is integrated during the LED On time, then

during the LED Off time, the integrated background energy is

subtracted from the LED On time energy, leaving the external

IR LED energy to accumulate from pulse to pulse.

After the programmed number of proximity pulses have been

generated, the proximity ADC converts and scales the proximity

measurement to a 16-bit value, then stores the result in two

8-bit proximity data (PDATAx) registers. ADC scaling is

controlled by the proximity ADC conversion time (PTIME) which

is programmable from 1 to 256 2.4-ms time units. However,

depending on the application, scaling the proximity data will

equally scale any accumulated noise. Therefore, in general, it is

recommended to leave PTIME at the default value of one 2.4-ms

ADC conversion time (0xFF).

Once the first proximity cycle has completed, the proximity

valid (PVALID) bit in the Status register will be set and remain

set until the proximity detection function is disabled (PEN).

For additional information on using the proximity detection

function behind glass and for optical system design guidance,

please see available ams application notes.

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