MP3204 – 6V, 1.3MHz WHITE LED DRIVER

MP3204 Rev. 1.3

www.MonolithicPower.com

7

9/23/2005

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© 2005 MPS. All Rights Reserved.

TM

Other applications require the use of a logic

signal to execute the dimming. This can be

seen in Figure 7. The PWM signal is applied to

the EN pin of the MP3204. The LEDs will switch

between full load to complete shutoff. The

average current through the LEDs will increase

proportionally to the duty cycle of the PWM

signal. The signal used in Figure 7 should be

1KHz or below due to the soft-start function.

PWM

MP3204

LED1

LED2

LED3

FB

MP3204_F07

EN

3

4

Figure 7—PWM Dimming Control Using a

Logic Signal

If the PWM signal is above 1KHz, dimming can

be achieved by using the circuit shown in

Figure 8.

PWM

MP3204

LED1

LED2

LED3

FB

3

MP3204_F08

Figure 8—Dimming Control Using a Filtered

PWM Signal

Open Load Protection

Open Load protection will shutoff the MP3204 if

the output voltage goes too high when the OV

pin is tied to the output. In some cases an LED

may fail, which will result in the feedback

voltage always being zero. The part will run at

the maximum duty cycle, boosting the output

voltage higher and higher. By tying the OV pin

to the top of the LED string the MP3204 checks

the said condition and if the output ever

exceeds 28V the MP3204 will shutdown. The

part will not switch on again until the power is

recycled. Figure 9 shows the behavior of the

MP3204 into an open load.

5V/div.

10V/div.

10V/div.

MP3204_F09

Figure 9—Startup Waveforms into an Open

Layout Considerations

Careful attention must be paid to the PCB

board layout and component placement. Proper

layout of the high frequency switching path is

critical to prevent noise and electromagnetic

interference

problems.

Due

to

the

high

frequency switching, the length and area of all

the traces connected to the switch node should

be minimized. Refer to the evaluation board

EV3204DJ-00A

for

a

sample

layout

of