12

 2005 Semtech Corp.

www.semtech.com

SC4901

POWER MANAGEMENT

Application Information (Cont.)

Fig 3b. Driving the Pulse Transformer with > 50% duty ratio using using a series capacitor

Fig 3c. Driving a Pulse Transformer with > 50% duty ratio using using a zener for reset

PGN D

DRES

DTO

RGS

RG

X F R A PIN IS PR OV IDED TO

SIM PLIF Y PU LSE

TR A N SF OR M ER DESIGN

X F R A IS A N O PEN C O LLEC TOR

THA T TU R N S ON W HEN OU TA

IS ON

F OR OPER A TIN G DU TY RA TIO S

OF > 5 0 % A Z EN ER M A Y B E

A DDED IN REV ER SE SERIES

W ITH D R ES A S SHO W N

X F R A PIN W ILL B E STR ESSED

TO PV C C + Z EN ER V OLTA GE

DU R IN G THE OFF PER IOD

GA TE VOLTAGE W ILL ALW A Y S

B E EQ U A L TO PV C C DU R IN G

ON TIM E IR R ESPEC TIV E OF

DU TY R A TIO

Curre nt

Se nse

QR

QF

CT

••

••

L

ZC D

15

CAO

3

CS -

2

CS +

1

OUT B

6

SSE N

4

XF RA

7

PVC C

9

PG ND

8

VC C

5

GN D

16

OUT A

10

RE F

11

VE A-

12

VE A

13

RC T

14

P W M L O G I C

A N D

O U T P U T

D R I V E R S

T RANSFORM ER

SECONDARY

SYNC AND RAM P

+

+-

-

QS

DVCC

COUT

RT

RZ

PV C C

VOU T

VSEC

RTN

SC 49 01

SIN GLE

EN DED

FOR W A R D

CO N V ER TOR

C SS

XF R A

Z RES

OPTION A L

PGN D

DRES

DTO

RGS

RG

X F R A PIN IS PR O V IDED TO

SIM P LIF Y PU LSE

TR A N SF O R M ER DESIGN

X F R A IS A N O PEN

COLLECTO R THA T TU R N S

O N W HEN O U TA IS O N

F O R OPE R A TIN G DU TY

R A TIOS OF > 50% A

CA PA CITOR CA N B E

C ON N EC TED IN SER IES

WITH PU LSE

TR A N SF O R M ER

'DR ES' A N D 'C R ES'

TOGETHER R ESE T THE

PU LSE XF R DU RIN G THE

O FF TIM E.

GA TE DR IV E V OLTA GE

A PPLIED IS R EDU C E D B Y

THE V OLTA GE A C R O SS 'C

R ES'. THIS HA PE N S O N LY

W HEN D > 50 %

Curre nt

Se n se

QR

QF

CT

••

••

ZCD

15

CAO

3

CS-

2

CS+

1

OUT B

6

SSE N

4

XFRA

7

PVCC

9

PGN D

8

VCC

5

GND

16

OUT A

10

RE F

11

VE A-

12

VE A

13

RCT

14

P W M L O G I C

A N D

O U T P U T

D R I V E R S

TRANSFO RMER

SECONDARY

SYNC AND RAM P

+

+-

-

L

QS

DVCC

COUT

RT

RZ

PV C C

VOU T

VSEC

RTN

SC 49 01

SIN GLE

EN DED

FO R W A R D

CON V ER TO R

C SS

XF RA

C R E S

OPTION A L