MP3302 –40V, 1.3A, SINGLE-CELL STEP-UP WHITE LED DRIVER WITH SINGLE WIRE DIMMING CONTROL

MP3302 Rev. 0.98

www.MonolithicPower.com

8

5/5/2010

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LED Current Programming

Applying a DC voltage between 0.7V and 1.4V

to EN pin programs a feedback voltage

between 0V and 200mV. Thus the analog

dimming of LED current can be achieved. The

DC dimming voltage must be locally bypassed

to prevent noise interfering with the feedback

reference level.

PWM Dimming

Apply a 200Hz to 1kHz square waveform to the

EN pin to implement PWM dimming of the

LEDs. The minimum recommended amplitude

of the PWM signal is 1.5V.

For high frequency PWM dimming (>1kHz), it is

also recommended that the dimming control be

implemented as shown in Figure 3. The cut off

frequency of the RC filter should be 10 times

lower than that of the input PWM signal. For

example, when the PWM frequency is 20kHz, a

20kΩ resistor and 100nF capacitor can be used.

The DC voltage on EN pin is then equal to the

PWM high level voltage multiplies the PWM

programs the output current from 0~100%.

PWM

MP3302

LED1

LED2

LED3

FB

EN

Figure 3—High Frequency PWM Dimming

Control

Open Load Protection

Open Load protection will shut off the MP3302

if the output voltage goes too high. In some

cases an LED may fail, this will result in the

feedback voltage always being zero. The part

will run at maximum duty cycle boosting the

output voltage higher and higher. If the output

ever exceeds 42V, the MP3302 will shut down.

The part will not switch again until the power is

recycled.

Layout Considerations

Careful attention must be paid to the PCB

board layout and components placement.

Proper layout of the high frequency switching

path

is

critical

to

prevent

noise

and

electromagnetic interference problems. The

current loop of IC, output diode, and output

capacitor should be as short as possible.

The IN pin of the IC must be locally bypassed.

A RC filter is highly recommended for

eliminating the noise on IN pin. It could be

implemented as shown in Figure 4.

MP3302

SW

GND

IN

Input

Figure 4—Input Bias Filtering