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AN1673

APPLICATION NOTE

April 2004

INTRODUCTION

Because of the much high efficiency that can be achieved (higher than the traditional PWM) and the re-

duction of the high frequency electromagnetic interference (thanks to the utilization of parasitic parameters

of the circuit), the interest for resonant topologies is recently growing in power conversion market. In fact

this kind of topologies allows high power/weight ratio and low power dissipation of the power parts.

Several power supply application segments such as Adapters, Television, Monitor, Telecom and Car Ra-

dio can benefit by using converters based on the topology.

The L6598 is designed for half bridge configuration.

This paper deals on how to use this device. At the end, it will be discussed concerning some design criteria

and application tips.

FEATURED DEVICE DESCRIPTION

The device, whose internal block diagram is shown in fig.1, is an integrated circuit realized in Off-Line tech-

nology. Able to drive Powermos or IGBT, in half bridge topology, it is provided with all the features (such

as VCO, Soft-Start, OP-Amp and Enables) needed to implement and control properly a resonant SMPS

with the minimum components count.

Even though the device is able to withstand high voltage, it can operate at low voltage starting from its

operative supply. It is available in DIP16 and SO16N packages.

The most significant peculiarities are:

– High voltage rail (up to 600V) and

immunity (± 50 V/ns) at full temperature range.

– 250 mA (source) / 450 mA (sink) driver current capability.

– Under voltage lockout.

– Precise current controlled oscillator and frequency shift for soft-star function.

– Integrated bootstrap driver for C-boot charging.

Figure 1. Internal Block diagram

dv

dt

------

VREF

Ifmin

Ifstart

OP AMP

12

VS

Cf

OPOUT

OPIN-

OPIN+

Rfmin

Rfstart

5

6

7

4

2

3

HVG

OUT

LVG

GND

EN1

EN2

1

9

8

10

11

14

15

16

Vthe1

LVG DRIVER

Vthe2

VBOOT

CBOOT

H.V. BUS

LOAD

VREF

VCO

UV

DETECTION

HVG

DRIVER

LEVEL

SHIFTER

+

+

-

+

-

-

DEAD

TIME

DRIVING

LOGIC

CONTROL

LOGIC

BOOTSTRAP

DRIVER

D03IN1429

L6598 OFF-LINE CONTROLLER FOR

RESONANT CONVERTERS