IRPLLED1A International Rectifier, IRPLLED1A Datasheet - Page 20

Manufacturer Part Number

IRPLLED1A

Description

Power Management IC Development Tools Hi-Vlt DC-DC Buck Cnvr HBLED Cur Cntrl

Manufacturer

International Rectifier

Type

DC/DC Converters, Regulators & Controllersr

Datasheet

1.IRPLLED1A.pdf (28 pages)

Product

Power Management Development Tools

Tool Is For Evaluation Of

IRS25401PBF

Output Voltage

16 V to 24 V

Output Current

350 mA to 1.5 A

Factory Pack Quantity

During PWM dimming operation care should be taken to avoid high current pulses occurring in the LED output at

the start of each dimming period. This occurs only when a capacitor is connected to the output, that is when the

jumper (Jdim) is in the REG position. Although the high side MOSFET is switched off the LED current continues to

rise due to resonant action between the output inductor and capacitor. If the jumper is left unconnected in either

REG or DIM positions there will be no output capacitor connected and in this case no overshoot occurs at the start

of each PWM dimming period. PWM dimming operation therefore should not be used with Jdim in the REG

position but instead leave this jumper unconnected or place it in the DIM position. In the DIM position a resistor is

added in series with the output capacitor to eliminate the high inrush current and consequent current surge in the

LEDs. The presence of high current surges may reduce LED life and cause the inductor to emit audible noise.

Figures 25-28 the LED load current and LO pin output at the start of a PWM dimming period to illustrate the

behaviour described.. The LO pin output is low when the high side MOSFET is on supplying current to the output.

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Fig. 25 Load Current Surge dimming with an output capacitor (REG position)

Fig. 26 Load Current Ripple with output capacitor in steady state

Iout = 350mA, Vin = 100V, Vout = 17V

RD-0608