AN727 データシートの表示（PDF） - Vishay Semiconductors

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AN727

High-Frequency, High-Efficiency Buck Converter Design For Multi-Cell Battery Configured Systems Using Si9167

Vishay Semiconductors 

AN727

Vishay Siliconix

FUNCTIONAL BLOCK DIAGRAM

VDD

SD

VIN

Positive Supply

1.3 V

Reference

Threshold

Generator

Soft-Start

Timer

UVLO

POR

Bias

Generator

System Monitor

OTP

VREF

VO

FB

COMP

SYNC

CLK

ROSC

Oscillator

COSC

1.0 V

Ramp

PWM

Modulator

0.5 V

PSM

Modulator

PWMIN

PWM/PFM

Select

PSMIN

PWMIN

Drivers

PSMIN

COIL

–

POKIN

+

POK

PWM/PSM

FIGURE 2.

Negative Return

and

Substrate

GND

PGND

DESIGN GUIDELINES

The following section describes key device features and

provides general guidelines for designing a buck regulator with

the Si9167.

Voltage Mode Control

For cellular phone and PDA applications, voltage-mode

control provides a number of advantages, including the

avoidance of power dissipation in current sensing elements,

greater noise immunity (since the PWM signal can be as high

as 1 V), and a less complicated single feedback loop to

compensate with.

The BiCMOS process used in the Si9167 improves

voltage-mode performance by increasing the operating

frequency and thereby pushing the closed loop bandwidth to

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2

more than 100 kHz. Since the intended applications for this

device involves a battery input, such that rapid changes in

voltage level are not involved, there is no need for a fast input

dynamic response as offered by current mode control.

1.0 V

+

–

0.5 V

Oscillator

FIGURE 3. Voltage Mode Control

Document Number: 70959

07-Jul-99

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