MP3202 – 1.3A FIXED FREQUENCY WHITE LED DRIVER

MP3202 Rev. 0.91

www.MonolithicPower.com

5

9/21/2007

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APPLICATION INFORMATION

OFF ON

MP3202

4V to 6V

MBR0520

9 Strings

Total

IN

EN

GND

OV

FB

SW

Figure 2—Circuit for Driving 27 WLEDs

A typical application circuit is provided in Figure

2. The 27 white LEDs can be driven from a

voltage supply range of 4V to 6V at a total

output current of 180mA. A 2.2µF output

capacitor is sufficient for most applications but

up to 1µF may be used. A 10µH inductor with

low DCR (inductor resistance) is recommended

to

improve

efficiency.

A

4.7µF

ceramic

capacitor is recommended for the input

capacitance in the real system. Schottky diodes

with fast recovery and a low forward voltage are

recommended. Schottky diodes with a 500mA

rating are sufficient for the MP3202. The

switching

characteristics

during

normal

operation can be seen in Figure 3. The MP3202

has internal soft-start to limit the amount of

current through the IN pin at startup and to also

limit the amount of overshoot on the output. The

current limit is increased by a fourth every 40µs

giving a total soft-start time of 120µs.

5V/div.

200mV/div.

500mA/div.

400ns/div.

Steady State Operation

Figure 3—Steady State Operation

Figure 4 shows the startup behavior of the

MP3202. The ramped voltage added to the

current sense amplifier reduces the current

output as the duty cycle increases. As more

LEDs are added, the output voltage rises but

the current that can be delivered to the load is

reduced as well.