APW7062B Ver la hoja de datos (PDF) - Anpec Electronics

Número de pieza

componentes Descripción

Fabricante

APW7062B

Synchronous Buck PWM Controller

Anpec Electronics 

APW7062B

Application Information

Component Selection Guidelines

∆VOUT = IRIPPLE x ESR

Output Capacitor Selection

The selection of COUT is determined by the required

effective series resistance (ESR) and voltage rating

rather than the actual capacitance requirement. There-

fore select high performance low ESR capacitors that

are intended for switching regulator applications. In

some applications, multiple capacitors have to be

paralled to achieve the desired ESR value. If tantalum

capacitors are used, make sure they are surge tested

by the manufactures. If in doubt, consult the capaci-

tors manufacturer.

Input Capacitor Selection

The input capacitor is chosen based on the voltage

rating and the RMS current rating. For reliable

operation, select the capacitor voltage rating to be at

least 1.3 times higher than the maximum input voltage.

The maximum RMS current rating requirement is ap-

proximately IOUT/2 , where IOUT is the load current.

During power up, the input capacitors have to handle

large amount of surge current. If tantalum capacitors

are used, make sure they are surge tested by the

manufactures. If in doubt, consult the capacitors

manufacturer.

For high frequency decoupling, a ceramic capacitor

between 0.1uF to 1uF can be connected between VCC

and ground pin.

Inductor Selection

The inductance of the inductor is determined by the

output voltage requirement. The larger the inductance,

the lower the inductor’s current ripple. This will trans-

late into lower output ripple voltage. The ripple current

and ripple voltage can be approximated by:

where Fs is the switching frequency of the regulator.

There is a tradeoff exists between the inductor’s ripple

current and the regulator load transient response time

A smaller inductor will give the regulator a faster load

transient response at the expense of higher ripple cur-

rent and vice versa. The maximum ripple current oc-

curs at the maximum input voltage. A good starting

point is to choose the ripple current to be approxi-

mately 30% of the maximum output current.

Once the inductance value has been chosen, select

an inductor that is capable of carrying the required

peak current without going into saturation. In some

type of inductors, especially core that is make of

ferrite, the ripple current will increase abruptly when it

saturates. This will result in a larger output ripple

voltage.

Compensation

The output LC filter introduces a double pole, which

contributes with –40dB/decade gain slope and 180

degrees phase shift in the control loop. A compensa-

tion network between COMP pin and ground should

be added. The simplest loop compensation network

is shown in Fig. 4.

The output LC filter consists of the output inductor

and output capacitors. The transfer function of the LC

filter is given by:

GAINLC =

1+ s × ESR × COUT

s2 × L × COUT + s × ESR + 1

IRIPPLE =

VIN - VOUT

Fs x L

x

VOUT

VIN

Copyright  ANPEC Electronics Corp.

11

Rev. A.3 - Mar., 2005

www.anpec.com.tw

Share Link: