PR4101 datasheet(14/24 Pages) PREMA

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LED Driver PR4101

Application Notes

SOFT START

With an external capacitor at RTK the output

current can ramp up continuously within a

programmable period.

The following table gives some capacitor values:

Soft Start Time

CSOFT

10 ms

100 nF

100 ms

1 µF

3 s

22 µF

possible

combine

temperature

compensation and softstart functionality. A soft

start is triggered by a reset that is initiated

either by applying the supply voltage, or by

starting the IC up with the PWRDWN signal.

Passing the threshold at VDI does not trigger

the soft start however, therefore supply by a

phase-cut voltage from a dimmer does not

interfere with soft start - see oscilloscope

diagram.

CORRESPONDING OSCILLOSCOPE IMAGES

Softstart on RTK, CSOFT = 100 nF

Softstart on RTK, CSOFT = 1 µF

(phase-cut input voltage)

--- Vcc

--- PwrDwn

--- LED current (voltage at a 1Ω resistor)

--- clock signal (test pin)

Measured with

CIN = 470 µF

CLED = 100 µF

C5VHi/Lo = 220 nF

L = 470 µH

Vcc = 15 V

RSENSE = 0.25 Ω

1 x 3 W Luxeon LED

Supply by a phase-cut voltage from a dimmer does not interfere with soft start - see right diagram.

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