MP3388S—50V, 8-STRING, WHITE LED DRIVERS

MP3388S Rev.1.01

www.MonolithicPower.com

14

10/29/2012

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Selecting the Output Capacitor

The output capacitor minimizes the output voltage

ripple and ensures a stable feedback loop. The

output capacitor impedance should be low at the

switching frequency. Use ceramic capacitors with

X7R dielectrics for their low ESR characteristics.

The output voltage ripple is estimated as:

IN

LED

OUT

RIPPLE

SW

V

1 -

I

V

V

C2 f













switching frequency, and C2 is the output

capacitor.

For most applications, use a 2.2μF ceramic

capacitor.

LAYOUT CONSIDERATIONS

Layout and component placement on the PCB

requires careful attention. Proper high-frequency

switching-path layout can prevent noise and

electromagnetic interference problems. The loop

from SW (U1), to the output diode (D1), to the

output capacitor (C3), to PGND (U1) carries a

high-frequency pulse current: minimize the loop

length and enclosed area (See Figure 10).

Figure 10: Sample Layout

The IC exposed pad is internally connected to

GND pin, and all logic signals are refer to the GND.

Externally connects PGND to GND, and avoid

placing PGND near logic signals.