MP3202 – 1.3A FIXED FREQUENCY WHITE LED DRIVER

MP3202 Rev. 0.91

www.MonolithicPower.com

4

9/21/2007

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OPERATION

The MP3202 uses a constant frequency, peak

current mode boost regulator architecture to

regulate the strings of white LEDs. Refer to the

block diagram in Figure 1 for details.

At the start of each oscillator cycle the FET is

turned on through the control circuitry. To

prevent sub-harmonic oscillations at duty cycles

greater than 50%, 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.

The voltage at the output of the error amplifier

is an amplified version of the difference

between the 104mV reference voltage and the

feedback voltage. In this way the peak current

level keeps the output in regulation.

If the feedback voltage starts to drop, the output

of the error amplifier increases. This results in

more current flowing through the power FET,

thus increasing the power delivered to the

output.

PWM

COMPARATOR

AMPLIFIER

CONTROL

LOGIC

CURRENT

SENSE

AMPLIFIER

SW

M1

GND

-

+

FB

1.3MHz

OSC

-

+

+

-

+

104mV

Figure 1—Functional Block Diagram