MP3306-

--

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

MP3306 Rev.1.0

www.MonolithicPower.com

7

3/6/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2013 MPS. All Rights Reserved.

OPERATION

The MP3306 uses a constant frequency, peak

current mode step up regulator architecture to

regulate the current flowing through series string of

white LEDs. The operation of the MP3306 can be

understood by referring to the block diagram of

Figure 1.

At the start of each oscillator cycle the low side FET

(M2) is turned on through the control circuitry. To

prevent sub-harmonic oscillations at duty cycles

greater than 50 percent, a stabilizing ramp is added

to the output of the current sense amplifier and the

result is fed into the positive input of the PWM

comparator. When this voltage equals the output

voltage of the error amplifier the power FET is

turned off. Then the inductor current flows into the

output capacitor and LED load through internal high

side N-channel MOSFET (M3), which forces the

inductor current to decrease.

The voltage at the output of the error amplifier is an

amplified version of the difference between the

200mV reference voltage and the feedback voltage.

In this way the LED current is regulated accurately.

If the feedback voltage starts to drop, the output of

the error amplifier increases. This result in more

current flowing through the high side power FET,

thus increasing the power charged in inductor and

delivered to the output.

MP3306 provides the analog and PWM dimming

solution, the internal resistor and external capacitor

one PWMO pin filters the PWM dimming signal on

PWMI pin to DC level that program the internal

reference to accomplish the analog dimming

function. When floating the PWMO pin, PWM

dimming function works.

Open Load protection shuts off the MP3306 if the

output voltage goes too high. In some cases an

LED may fail, this results in the feedback voltage

always being zero. The part then runs at maximum

duty cycle boosting the output voltage up. If the

output ever exceeds the programmable OVP

threshold, the MP3306 will shut down. The part

toggled.

During Shutdown mode when EN is low, the IC

keeps the internal high-side N-channel MOSFET

(M1) off to disconnect the output from input.

MP3306 has cycle by cycle current limit to protect

the load and IC from over current. And the internal

MOSFET (M1) limits the input current to prevent