MP3301

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

MP3301 Rev. 1.01

www.MonolithicPower.com

6

10/28/2013

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OPERATION

The MP3301 uses a constant-frequency, peak-

current

–mode, boost-regulator architecture to

regulate up to 10 white LEDs in series. Figure 1

shows how the MP3301 operates.

The MP3301 regulates the SW voltage through

the feedback voltage and the 1.3MHz oscillator.

At the start of each oscillator cycle, the control

circuitry turns the FET on. A stabilizing ramp

added to the output of the current sense

amplifier prevents sub-harmonic oscillations at

duty cycles >50%: The ramp output goes to the

positive input of the PWM comparator: When

this voltage equals the error amplifier output

(the amplified difference between the 200mV

reference voltage and the feedback voltage),

the power FET turns off.

When the feedback voltage starts to drop, the

output of the error amplifier increases, thus

increasing the current flowing through the

power FET. The increased FET power results in

increased power delivered to the output.

Figure 1: Functional Block Diagram