TSL27721 datasheet(22/58 Pages) OSRAM

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Datasheet, Public

Page 21

[v2-00] 2023-Mar-30

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TSL2772 − Principles Of Operation

Figure 24:

Proximity LED Current Driver Waveform

Figure 23 illustrates light rays emitting from an external IR LED,

reflecting off an object, and being absorbed by the CH0 and

CH1 photodiodes. The proximity diode selector (PDIODE)

determines which of the two photodiodes is used for a given

proximity measurement. Note that neither photodiode is

selected when the device first powers up, so PDIODE must be

set for proximity detection to work.

Referring again to Figure 24, 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. The proximity

gain (PGAIN) determines the integration rate, which can be

programmed to 1x, 2x, 4x, or 8x gain. At power up, PGAIN

defaults to 1x gain, which is recommended for most

applications. For reference, PGAIN equal to 8x is comparable to

the TSL2771 1x gain setting. During LED On time integration,

the proximity saturation bit in the Status register (0x13) will be

set if the integrator saturates. This condition can occur if the

proximity gain is set too high for the lighting conditions, such

as in the presence of bright sunlight. Once asserted, PSAT will

remain set until a special function proximity interrupt clear

command is received from the host (see Command Register).

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 2.73-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

LED On

LED Off

IR LED Pulses

Background

Energy

Reflected IR LED +

Background Energy

16.0

7.3

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