MP3302 –40V, 1.3A, SINGLE-CELL STEP-UP WHITE LED DRIVER WITH SINGLE WIRE DIMMING CONTROL

MP3302 Rev. 0.98

www.MonolithicPower.com

7

5/5/2010

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APPLICATION INFORMATION

Enable/

Dimming

Control

MP3302

3.3V to 6V

MBR0520

4.7uH

C2

0.47uF

C1

10uF

IN

EN

GND

FB

SW

Figure 2—Circuit for Driving 9 Strings of 3 WLEDs

A typical application circuit can be seen in

Figure 2. The 9 strings of 3 white LEDs can be

driven from a voltage supply range of 3.3V to

6V at an output current of 180mA. A 0.47µF

output

capacitor

is

sufficient

for

most

applications. A 4.7µH inductor with low DCR

(Inductor DC resistance) is recommended to

improve efficiency. A 10µF ceramic capacitor is

recommended for the input capacitance in the

real system. Schottky diodes have fast recovery

and

a

low

forward

voltage

and

are

recommended. Schottky diodes rated with

500mA are sufficient for the MP3302. The

MP3302 has internal soft-start to limit the

amount of current through VIN at startup and to

also limit the amount of overshoot on the output.

The ramped voltage that is 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.

Setting the LED Current

The LED current is controlled by the feedback

resistor, R1. The current through the LEDs is

given by the equation 200mV/R1. Table 1

shows the selection of resistors for a given LED

current.

R1 (Ω)

1

200

5

40

10

20

20

10

60

3.33

180

1.11