TCS37715FN datasheet(38/49 Pages) OSRAM

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ams Datasheet

Page 37

[v1-31] 2018-Apr-04

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TCS3771 − Application Information

LED Driver Pin with Proximity Detection

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

TCS3771 with more than 100mA 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 1μF low-ESR

decoupling capacitor as close as possible to the VDD pin and

another at the LED anode, and a 22μF capacitor at the output

of the LED voltage regulator to supply the 100mA current surge.

Figure 44:

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 22Ω resistor in

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

effectively filter any power supply noise. The previous capacitor

placement considerations apply.

Figure 45:

Proximity Sensing Using Single Power Supply

Application Information

TCS37715FN Datasheet(PDF) 38 Page - OSRAM GmbH