MP3306-

--

-30V 700kHz SYNCHRONOUS STEP-UP WHITE LED DRIVER

MP3306 Rev.1.0

www.MonolithicPower.com

9

3/6/2013

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© 2013 MPS. All Rights Reserved.

Current Limit vs. Duty

0 10 20 30 40 50 60 70 80 90100

0

0.5

1

1.5

2

Figure 3—Current Limit Curve

Analog and PWM Dimming

MP3306 provides 2 types of dimming solutions,

analog dimming and PWM dimming.

For analog, connect an external capacitor on

PWMO pin to form the low pass filter with internal

resistor R, the PWM dimming signal on PWMI pin

is filtered to DC signal to set the internal

reference to accomplish the analog dimming. The

time constant should be ten times greater than a

PWM waveform cycle:

PWM

RC

10 T

>

⋅

For PWM dimming, floating PWMO pin and apply

the PWM dimming signal on PWMI pin.

Setting Over Voltage Protection Threshold

Open Load protection will shut off the MP3306 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 boots the

output voltage higher and higher. If the output

voltage ever exceeds the programmed OVP

threshold as the formula,

OVP

V

=1.22 (1 R2 / R3)

×

+

The MP3306 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 loop of MP3306’s internal low side

MOSFET, synchronous MOSFET, and output

capacitor is flowing with high frequency ripple

current, it must be minimized. So the output

capacitor should be placed to IC as close as

possible.