MP24833 – 3A, 55V WHITE LED DRIVER

MP24833 Rev. 1.0

www.MonolithicPower.com

14

05/05/2010

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DESIGN EXAMPLE

Below is a schematic for a white LED driver that

is compatible with step-down, step-up/down, and

step-up application.

• For step-down application, short “JP1”,

open “JP2”, connect LED load to “LED+”

and “LED-”

• For step-up/down application, short “JP2”,

open “JP1”, connect LED load to “LED+”

and “LED-”

• For step-up application, short “JP2”, open

“JP1”, connect LED load to “LED+_Boost”

and “LED-”.

BST

OVP

SW

VDD

EN/DIM

INGND

VSS

1

6

2

FB

4

8

7

3

5

VIN

C

2

2.2uF

C

C

1

NC

EN/DIM

R

1

R

2

INGND

0

10k

VSS

VSS

R

3

0

JP1

C

5

4.7uF

VSS

JP2

LED+

B360

LED-

R

4

10k

R

6

400m

R

7

400m

NC

R

9

R

8

226k

LED+_Boost

R

10

NC

R

5

1k

VSS

68uH

D

2

NC

L

1

D

1

C

3

2.2uF

Figure 6: Design Example White LED Driver;

Compatible with Step-Down, Step-Up/Down and Step-Up Application

Use the step-up/down application for example to

show the design procedure.

Specifications

Input: 24V, DC;

Output: LED current 1A maximum, LED voltage

24V;

Operating frequency: ~200 kHz.

Selecting LED Current Sense Resistor

Determine the LED current sense resistor from

the following equation

sense

LED

0.198V

R200mΩ

I

=≈

Considering power consumption, use two 400mΩ

resistors with 1206 package in parallel for LED

current sense resistor.

Selecting Inductor

The converter operates in continuous current

mode (CCM), determine the inductor value as

follows:

S

IN

OUT

IN

OUT

L

VV

L

(V

V

)

I

f

×

=

+

×Δ ×

Where

ripple. Select

60%) of the inductor average current, which is:

OUT

L _ AVG

LED

IN

V

II

(1

)

V

=⋅ +

.