AN723 データシートの表示（PDF） - Vishay Semiconductors

部品番号

コンポーネント説明

メーカー

AN723

Design A High Performance Buck or Boost Converter With Si9165

Vishay Semiconductors 

AN723

Vishay Siliconix

FIGURE 3. Typical Application Circuit—Boost

DESIGN GUIDELINES

Following are some design guidelines for buck and boost

converters. The Si9165 combines a high level of integration

while allowing the designer a considerable measure of

flexibility. Key components required for a complete converter

design are an inductor, input/output capacitors, and a

compensation network.

Inductor Selection

An inductor is the energy storage component in a converter.

Choosing an inductor means specifying its size, structure,

material, inductance, saturation level, dc-resistance (DCR),

and core loss. Fortunately, there are many inductor vendors

that offer wide selections with ample specifications and test

data, such as Vishay-Dale, Coilcraft, Coiltronics, and Sumida.

The following are some key parameters that users should

focus on.

In PWM mode, inductance has a direct impact on the ripple

current. The peak-to-peak inductor ripple current can be

calculated as

For Buck, Ip – p

=

-V----O----U---T---(---V----I--N----–-----V----O----U----T---)

VINLF

(1)

For Boost, Ip – p

=

-V----I-N-----⋅---(--V-----O---U----T----–-----V----I--N---)-

VOUTLF

(2)

where f = switching frequency.

Higher inductance means lower ripple current, lower rms

current, lower voltage ripple on both input and output, and

higher efficiency, unless the resistive loss of the inductor

dominates the overall conduction loss. However, higher

inductance also means a bigger inductor size and a slower

response to transients. In PSM mode, inductance affects

inductor peak current, and consequently impacts the load

capability and switching frequency. For fixed line and load

conditions, higher inductance results in a lower peak current

for each pulse, a lower load capability, and a higher switching

frequency.

The saturation level is another important parameter in

choosing inductors. Note that the saturation levels specified in

datasheets are maximum currents. For a dc-to-dc converter

operating in PWM mode, it is the maximum peak inductor

current that is relevant, and which can be calculated using

these equations:

For Buck, Ipk

=

IOUT

+

-I-p----–---p-

2

(3)

For Boost, Ipk

=

V-----O----U---T---I--O----U----T- + -I-p----–---p-

ηVIN

2

(4)

where η = converter efficiency.

This peak current varies with inductance tolerance and other

errors, and the rated saturation level varies over temperature.

So a sufficient design margin is required when choosing

current ratings.

A high-frequency core material, such as ferrite, should be

chosen, since at 2 MHz, the core loss could lead to serious

efficiency penalties. The DCR should be kept as low as

possible to reduce conduction losses.

FaxBack 408-970-5600, request 70823

www.siliconix.com

3

Share Link: