PT4115BSOH-B 查看數據表（PDF） - Unspecified

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PT4115BSOH-B

30V, 1.2A Step-down High Brightness LED Driver with 5000:1 Dimming

Unspecified 

PT4115

30V, 1.2A Step-down High Brightness

LED Driver with 5000:1 Dimming

APPLICATION NOTES

Setting nominal average output current with

external resistor RS

The nominal average output current in the LED(s) is

determined by the value of the external current sense

resistor (RS) connected between VIN and CSN and is

given by:

IOUT  0.1/ Rs (Rs  0.082)

This equation is valid when DIM pin is float or applied

with a voltage higher than 2.5V (must be less than 5V).

Actually, RS sets the maximum average current which

can be adjusted to a less one by dimming.

Output current adjustment by external DC control

voltage

The DIM pin can be driven by an external dc voltage

(VDIM), as shown, to adjust the output current to a

value below the nominal average value defined by RS.

VIN

RS

0.13Ω

LED

3W

D

L

68uH

cycle PWM can be applied to the DIM pin, as shown

below, to adjust the output current to a value below the

nominal average value set by resistor RS:

I

OUT 

0.1

Rs

D

(0  D  100%,2.5V  Vpulse  5V )

I OUT

 Vpulse  0.1 D

2.5 Rs

(0  D  100%,0.5V  Vpulse  2.5V )

RS

VIN

0.13Ω

LED

3W

L

68uH

D

VIN

CSN

SW

DIM

PT4115

VIN

CSN

SW

GND

DIM

PT4115

GND

The average output current is given by:

I OUT

 0.1VDIM

2.5  Rs

(0.5V  VDIM

 2.5V )

Note that 100% brightness setting corresponds to:

(2.5V  VDIM  5V )

Output current adjustment by PWM control

A Pulse Width Modulated (PWM) signal with duty

PWM dimming provides reduced brightness by

modulating the LED’s forward current between 0% and

100%. The LED brightness is controlled by adjusting

the relative ratios of the on time to the off time. A 25%

brightness level is achieved by turning the LED on at

full current for 25% of one cycle. To ensure this

switching process between on and off state is invisible

by human eyes, the switching frequency must be

greater than 100 Hz. Above 100 Hz, the human eyes

average the on and off times, seeing only an effective

brightness that is proportional to the LED’s on-time

duty cycle. The advantage of PWM dimming is that the

forward current is always constant, therefore the LED

color does not vary with brightness as it does with

analog dimming. Pulsing the current provides precise

brightness control while preserving the color purity.

The dimming frequency of PT4115 can be as high as 20

kHz.

China Resources Powtech (Shanghai) Limited

PT4115_DS Rev EN_2.9

WWW.CRPOWTECH.COM

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