MP4601 – WHITE LED DRIVER FOR LARGE SIZE TV BACKLIGHTING

MP4601 Rev. 1.0

www.MonolithicPower.com

13

1/28/2011

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Where

ripple. Design

inductor average current, which is:

OUT

L _ AVG

LED

IN

V

II

(1

)

V

=⋅ +

.

Make sure the inductor is not saturated at the

maximum peak current, which is:

L_ PK

L_ AVG

L

II

0.5

I

=+

Selecting the Input Capacitor

The input capacitor reduces the surge current

drawn from the input supply and the switching

noise from the device. Ceramic capacitors with

X5R

or

X7R

dielectrics

are

highly

recommended because of their low ESR and

small

temperature

coefficients.

Enough

capacitance is required for limited input voltage

ripple

5~10% of the DC value.

L_ AVG

OUT

IN

sIN

IN

OUT

IV

C

fV (V

V

)

⋅

>

⋅∆

⋅

+

Selecting the Output Capacitor

The output capacitor keeps the output voltage

ripple

the DC value) and ensures feedback loop

stable. The output capacitor impedance should

be low at the switching frequency. Ceramic

capacitors with X5R or X7R dielectrics are

recommended for their low ESR characteristics.

LED

OUT

OUT

sOUT

IN

OUT

IV

C

fV

(V

V

)

⋅

>

⋅∆

⋅

+

PC Board Layout

The high current paths (VSS, VDD and SW)

should be placed very close to the device with

short, direct and wide traces. The input

capacitor needs to be as close as possible to

the VDD and VSS pins. The external feedback

resistors should be placed next to the FB pin.

Keep the switch node traces short and away

from the feedback network.