TMD26721 datasheet(16/44 Pages) OSRAM

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[v1-00] 2015-Mar-23

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TMD2672 − Principles of Operation

Figure 20:

Proximity LED Current Driver Waveform

Figure 19 illustrates light rays emitting from the internal 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 20, 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 IR LED

energy to accumulate from pulse to pulse. During LED On time

integration, the proximity saturation bit in the Status

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 2.73ms 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 2.73ms

ADC conversion time (0xFF).

LED On

LED Off

IR LED Pulses

Background

Energy

Reflected IR LED +

Background Energy

16.0

7.3

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