MP3301

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

MP3301 Rev. 1.01

www.MonolithicPower.com

7

10/28/2013

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APPLICATION INFORMATION

VIN

2.5~6V

MP3301

En/Dim

L1

D1

C1

4.7µF

C2

0.47µF

R1

10

Ω

IN

SW

FB

GND

EN

LED1~8

4.7µH

Figure 2: Circuit to Drive 8 WLEDs in Series

Figure 2 shows a typical application circuit. The

8 white LEDs can be driven from a 2.7V-to-6V

supply range at an output current of 20mA. A

0.47µF output capacitor is sufficient for most

applications. A 4.7µH inductor with low direct-

current resistance (DCR) improves efficiency,

while a 4.7µF ceramic capacitor improves input

stability. Use Schottky diodes with fast recovery

times and low forward voltages, preferably

rated at 500mA. The MP3301 has an internal

soft-start to limit the current through VIN at

startup and to also limit the output overshoot.

The ramped voltage at the current sense

amplifier reduces the current output as the duty

cycle increases. Adding more LEDs increases

the output voltage but reduces the current

delivered to the load.

Setting the LED Current

The feedback resistor, R1, controls the LED

current. The equation

1

200

R

mV

estimates the

current through the LEDs. Table 1 shows the

resistor selection for a given LED current.

R1 (

Ω)

1

200

5

40

10

20

20

10

60

3.33