MP3301

—1.3MHZ, 700MA, FIXED-FREQUENCY, STEP-UP DRIVER FOR WHITE LEDS

MP3301 Rev. 1.01

www.MonolithicPower.com

8

10/28/2013

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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 for analog dimming of

LED current. Locally bypass the DC dimming

voltage to limit noise on the feedback reference.

PWM Dimming

Apply a 200Hz-to-1kHz square waveform to the

EN pin to implement PWM dimming. Use a

PWM amplitude of at least 1.5V.

For high-frequency PWM dimming (>1kHz),

implement the dimming control shown in Figure

3.

Select the RC filter’s cut-off frequency

≤

10

PWM

f

. For example, for a PWM frequency of

20kHz,

use

a 20kΩ resistor and 100nF

capacitor. Then

PWM

high

_

PWM

EN

D

V

V





1.4V programs the output current from 0% to

100%.

Figure 3: Control Circuit for High-Frequency

PWM Dimming

Open-Load Protection

Open-load protection shuts off the MP3301 if

the output voltage goes too high. In cases

where an LED may fail, this results in a zero

feedback

voltage.

The

part

runs

at

the

maximum duty cycle to continue increasing the

output voltage. If the output exceeds 42V, the

MP3301 will shut down. The part will not switch

on again until the device undergoes a power

cycle.

Layout Considerations

PCB layout requires care to prevent noise and

electromagnetic interference from the high-

frequency switching paths. Make the current

loop from the IC, output diode, and the output

capacitor as short as possible.

Locally bypass the IN pin, and use an RC filter

when possible to eliminate noise on the IN pin.

See Figure 4 for an implementation example.

Figure 4: Input Bias Filtering