TSL27711 datasheet(19/51 Pages) OSRAM

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[v1-00] 2016-Mar-22

TSL2771 − Principles O f 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.

The number of LED pulses can be programmed to any value

between 1 and 255 pulses as needed. Increasing the number of

LED pulses at a given current will increase the sensor sensitivity.

Sensitivity grows by the square root of the number of pulses.

Each pulse has a 16-

μs period.

Figure 21:

Proximity IR LED Waveform

The proximity integration time (PTIME) is the period of time that

the internal ADC converts the analog signal to a digital count.

It is recommend that this be set to a minimum of PTIME = 0xFF

or 2.72 ms.

The combination of LED power and number of pulses can be

used to control the distance at which the sensor can detect

proximity. Figure 22 shows an example of the distances covered

with settings such that each curve covers 2x the distance.

Counts up to 64 pulses provide a 16x range.

LED On

LED Off

IR LED Pulses

Subtract

Background

Add IR +

Background

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