MP3306-

--

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

MP3306 Rev.1.0

www.MonolithicPower.com

8

3/6/2013

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

© 2013 MPS. All Rights Reserved.

APPLICATION INFORMATION

VIN

EN

DIM

GND

LED+

LED-

TP6

TP5

TP4

TP3

TP2

TP1

U1

MP3306

L

1

2

3

4

5

6

8

7

10

11

9

12

SW

BS T

OU T

IN

VCC

EN

PWMI

PWMO

OV P

GND

FB

JP1

C6

10nF

R1

51k

R5

0

R3

51k

R8

205k

R9

10k

C5

NS

R7

NS

R2

0

R4

NS

Figure 2—3V~12V Input, Typical Application Driving 8 WLEDs in series

Figure 2 shows a typical application circuit that

can drive up to 8 white LEDs with 20mA. A

0.22~2.2 F output capacitor is sufficient for most

applications. The inductor with low DC inductor

resistance (DCR) will improve efficiency. Two

4.7µF ceramic capacitors provide sufficient input

decoupling.

Selecting the Inductor

The inductor forces a higher output voltage

driven from a lower input voltage. A larger

inductor value results in less ripple current, a

lower peak inductor current, and reduces stress

on the internal N-Channel MOSFET. However,

larger-value

inductor has

a

larger

physical

footprint, higher series resistance, and lower

saturation current.

Choose an inductor that does not saturate under

the worst-case load conditions. Calculate the

required inductance value using the following

equations:

2

OUT

SW

LOAD

η V

D (1 D)

L

2

f

I

×

×

× −

≥

×

×

IN

OUT

V

D

1

V

= −

the LED load current, and η is the efficiency.

Setting the LED Current

The LED current is controlled by the current

setting resistor, R1. The current through the

Table 1 shows the selection of resistors for a

given LED current.

R1 ( )

1

200

5

40

10

20

20

10

60

3.33

180

1.11

200

1

The

internal

ramped

compensation

voltage

added to the current sense amplifier reduces the

maximum output current as the duty cycle

increases. As more LEDs are added, the output

voltage rises but the maximum current delivered

to the load falls as well. Figure 3 shows the

current limit curve, and the max LED current is

gotten as the formula.

IN

LOAD(max)

PK

SW

V

D

I

(I

) (1 D) 0.8

2 L f

×

=

−

×

−

×

× ×

cycle from current limit curve, the L is inductor,

the

0.8

means

the

margin

coefficient.