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Microsemi Corporation - PHASE MODULATED AC SYNCHRONOUS SECONDARY-SIDE CONTROLLER

Numéro de référence LX1571
Description PHASE MODULATED AC SYNCHRONOUS SECONDARY-SIDE CONTROLLER
Fabricant Microsemi Corporation 
Logo Microsemi Corporation 





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LX1571 fiche technique
T H E I N F I N I T E P O W E R O F I N N O VAT I O N
P ATENT PENDING
L I N D O C #: 1570
LX1570/1571
PHASE MODULATED AC SYNCHRONOUS SECONDARY-SIDE CONTROLLER
PR E L I M I N A RY D ATA S H E E T
DESCRIPTION
The LX1570/71 series of controller ICs are
designed to provide all control functions in
a secondary-side regulator for isolated auxil-
iary or secondary power supplies. Auxiliary
or secondary-side controllers are used in a
variety of applications including multiple
output off-line power supplies, commonly
found in desktop computers, as well as tele-
communications applications. Although they
can be used in all secondary output applica-
tions requiring precision regulation, they are
mainly optimized for outputs delivering more
than 3A current where standard three-termi-
nal regulators lack the desired efficiency. For
these applications, the Mag Amp regulators
have traditionally been used. However, Mag
Amps have several disadvantages. First, be-
cause they have to withstand the maximum
input voltage during a short-circuit condition,
they are "over designed", typically by 2 times,
increasing the cost and size of the power
supply. Second, Mag Amps are inherently
leading edge modulators, so they can only
approach a certain maximum duty cycle, lim-
ited by the minimum delay and the mag-
netic BH loop characteristic of the Mag Amp
core. This forces an increase in the size of
the main transformer as well as the output
inductor, resulting in higher overall system
cost. The LX1570/71 eliminates all the
disadvantages of the Mag Amp approach
as well as improving system perfor-
mance and reducing overall system cost.
The LX1570/71 is a current mode control-
ler IC that controls the duty cycle of a switch
in series with the secondary AC output of
the power transformer in buck-derived ap-
plications, such as forward or bridge topolo-
gies. It offers features such as 100% duty
cycle operation for maximum energy trans-
fer, pulse-by-pulse and hiccup current limit-
ing with long off-time between the cycles
for reduced power dissipation, high-fre-
quency operation for smaller magnetics, soft-
start, and current mode control for excel-
lent dynamic response.
PRODUCT HIGHLIGHT
Aux Output
12V/8A
OUT
DRV
VCC
C.S.
VFB
LX1571
COMP
CT S.S.
GND
KEY FEATURES
p REPLACES COSTLY MAG-AMP CORES WITH
A LOW ON-RESISTANCE MOSFET
p LOOK-AHEAD SWITCHINGTM ENSURES
SWITCH TURN ON BEFORE THE AC INPUT
TO ACHIEVE 100% ENERGY TRANSFER
p LOWER OVERALL SYSTEM COST
p LOWER PEAK CURRENT STRESS ON THE
PRIMARY SWITCH
p ALLOWS HIGHER OPERATING FREQUENCY
AND SMALLER OUTPUT INDUCTOR
p EASY SHORT-CIRCUIT PROTECTION
p CURRENT MODE APPROACH ACHIEVES
EXCELLENT DYNAMIC RESPONSE
A P P L I C AT I O N S
s SECONDARY-SIDE REGULATOR IN OFF-LINE
POWER SUPPLIES
s COMPUTER POWER SUPPLIES, 3.3V OUTPUT
FOR NEW LOW-VOLTAGE PROCESSORS
AND MEMORIES
s TELECOMMUNICATION AND MILITARY
DC/DC CONVERTERS
A VA I L A B L E OP T I O N S P E R P A R T #
Part #
C.L.
Threshold
C.S.
Option
Application
LX1570 -0.2V
Resistive
Sensing
Output
Currents
< 4A
Current Output
LX1571 1V Transformer Currents
Sensing > 4A
Copyright © 1997
Rev. 0.9.3 1/97
TA (°C)
0 to 70
-40 to 85
-55 to 125
PACKAGE ORDER INFORMATION
M
Plastic DIP
8-pin
DM
Plastic
8-pin
SOIC
Y
Ceramic DIP
8-pin
LX157xCM
LX157xCDM
LX157xIM
LX157xIDM
— — LX157xMY
Note: All surface-mount packages are available in Tape & Reel.
Append the letter "T" to part number. (i.e. LX157xCDMT)
FOR FURTHER INFORMATION CALL (714) 898-8121
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841
1

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