TSL27721 datasheet(43/56 Pages) AMSCO

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ams Datasheet

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[v1-00] 2016-Aug-26

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TSL2772 − Application Information Hardware

LED Driver Pin with Proximity Detection

In a proximity sensing system, the IR LED can be pulsed by the

TSL2772 with more than 100 mA of rapidly switching current,

therefore, a few design considerations must be kept in mind to

get the best performance. The key goal is to reduce the power

supply noise coupled back into the device during the LED

pulses.

The first recommendation is to use two power supplies; one for

the device VDD and the other for the IR LED. In many systems,

there is a quiet analog supply and a noisy digital supply. By

connecting the quiet supply to the VDD pin and the noisy supply

to the LED, the key goal can be meet. Place a 1-

μF low-ESR

decoupling capacitor as close as possible to the VDD pin and

another at the LED anode, and a 22-

μF capacitor at the output

of the LED voltage regulator to supply the 100-mA current

surge.

Figure 47:

Proximity Sensing Using Separate Power Supplies

If it is not possible to provide two separate power supplies, the

device can be operated from a single supply. A 22-

Ω resistor in

series with the VDD supply line and a 1-μF low ESR capacitor

effectively filter any power supply noise. The previous capacitor

placement considerations apply.

Application Information

Hardware

TSL2772

INT

SDA

SCL

VDD

LDR

Voltage

Regulator

Voltage

Regulator

. 22 mF

* Cap Value Per Regulator Manufacturer Recommendation

IR LED

GND

VBUS

RPI

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