MP2910 – 5V/12V SYNCHRONOUS BUCK PWM DC-DC AND LINEAR POWER CONTROLLER

MP2910 Rev. 1.0

www.MonolithicPower.com

12

12/14/2011

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© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Setting the Output Voltage

The output voltage is set by using a resistive

voltage divider from the output voltage to FB pin.

First, choose a value for the feedback resistor R6,

e.g. 10kΩ, and then R5 is determined as follows:

OUT

REF

56

REF

V-V

R=

R

V



Selecting the Inductor

An inductor with a DC current rating of at least

25% higher than the maximum load current is

recommended for most applications. A larger

value inductor will result in less ripple current and

lower output ripple voltage. However, the larger

value inductor has a larger physical size, higher

series resistance, and/or lower saturation current.

Generally, choose the inductor ripple current

approximately 30% of the maximum load current,

then the inductance value can be calculated by:

OUT

IN

OUT

IN

L

S

V(V - V

)

L

V

ΔIf







and

L

ΔI

is the peak-to-peak inductor ripple

current.

The maximum inductor peak current is:

L

L(MAX)

LOAD

ΔI

I=I

+

2

Input Capacitor Selection

Since the input capacitor absorbs the input

switching current, it requires an adequate ripple

current rating. The selection of input capacitor is

mainly based on its maximum ripple current

capability. The RMS value of ripple current

flowing through the input capacitor is described

as:

OUT

OUT

RMS

LOAD

IN

IN

VV

I=I

(1-

)

VV

selected must be capable of handling this ripple

current.

Output Capacitor Selection

The output capacitor keeps output voltage ripple

small and ensures regulation loop stability. The

output capacitor impedance should be low at the

switching frequency. The output voltage ripple

can be estimated by:

OUT

OUT

OUT

ESR

SIN

S

O

VV

1

ΔV1

R

fL

V

8 f

C





 









 

 

value of the output capacitor.

For tantalum or electrolytic capacitor application,

the ESR dominates the impedance at the

switching frequency. So the above formula can

be approximated as:

OUT

OUT

OUT

ESR

SIN

VV

ΔV1

R

fL

V



 









PCB Layout Guide

PCB layout is very important to achieve stable

operation.

A

multi-layer

PCB

is

highly

and SW) should be placed very close to the

device with short, direct and wide traces. A RC

external feedback resistors should be placed

next to the FB and FBL pins.

Below PCB layout files are our test board for your

reference: