MP2115 – 2A, 6V SYNCHRONOUS STEP-DOWN CONVERTER

MP2115 Rev. 1.0

www.MonolithicPower.com

10

2/28/2011

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Input Capacitor Selection

The input capacitor (C1) reduces the surge

current drawn from the input and switching

noise from the device. The input capacitor

impedance at the switching frequency must be

less than input source impedance to prevent

high frequency switching current passing to the

input. Ceramic capacitors with X5R or X7R

dielectrics are highly recommended because of

their

low

ESR

and

small

temperature

coefficients. For most applications, a 10µF

capacitor is sufficient.

VSYS Capacitor Selection

The VSYS capacitor C2 is used to supply the

USB port and with the peak output current,

such as during the TDM frame. That output

peak current is about 2A. Use three 470µF

capacitors to avoid large voltage drops.

Output Capacitor Selection

The output capacitor (C4) keeps output voltage

ripple small and ensures regulation loop stable.

The output capacitor impedance should remain

low at the switching frequency. Ceramic

capacitors with X5R or X7R dielectrics are

approximately:

(

)

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

×

+

×

×

×

−

×

≤

∆

2

C

f

8

1

ESR

L

f

V

V

V

V

V

OSC

OSC

IN

OUT

IN

OUT

OUT